New system tripping on low pressure??

[Willsmithiraq]

Guys,

Wisdom required please guys. Stuck in Afghanistan on me todd and require some help. I have a new install of a Ferroli condensor unit and an external evaporator drawing ambient air into the unit and supplying into the space via ductwork (for a kitchen).

Unit is R410a 53Kw. The unit is a heat pump and I have installed all the TXV, filter, sg, check valve etc. All purged with nitro, pressure tested, and vacced correctly. I've released the refrigerant and run the system up but it keeps tripping on low pressure after five minutes or so.

Suction 70 psi going down to 50 psi which is the cutout
Discharge 285 psi

Liquid line temp at TXV 31 C
After TXV -2 C
Exit evap - 9 C

Subcooling 4 C
Superheat - None??

Air on cond - 20 C
Air off cond - 36 C

Air On Evap - 20 C
Air Off Evap - 9 C

I'm getting excessive frosting on suction and compressor housing. Suggesting to me a couple of things.

1. Evap fan not creating enough air flow over coil or undersized.
2. Partially blocked TXV

I have a full sight glass and the filters in the evap are brand new.

Any thoughts or help that you can provide would be brilliant. Just praying that I haven't damaged the TXV when brazing it in even though I had it ragged up to the hilt!!

[lana]

Hi there,

From your info, it seems that you have a fault called " Lack of evaporator capacity". Of course if you don't have super heat. When LP goes down and super heat decreases, means there is not enough evaporation in the evaporator.
Again check the super heat carefully.

This fault can be due to :
1- Lack of enough air flow through evap. If this is the case then the air temperature difference through the evap will increase, i.e. 20 in and 6 out. If you have around 10°C difference then it is not the air flow.
2- Dirty evap, which makes the temperature difference of air to decrease, i.e. 20 in 15 out.
2- High pressure drop in the ducting system, which causes lower air flow and the symptoms are the same as NO1.
3- Excessive oil in the evaporator, which causes low heat exchange.
4- Problem with the fan (same as no1)
5- Dirty air filter
6- Fan running in the wrong direction.
7- Wrong electrical connection of the fan motor which makes the RPM to lower.

Again I repeat check the super heat, if super heat is high then the fault would be completely different.
If you suspect the TEV then this makes the super heat to increase NOT decrease.

Cheers

[Willsmithiraq]

Thanks Iana,

Apologies the superheat of the system is about 1K after looking at it again. The evap is clean and new and the same for the filters, the fan is also running in the correct direction.

[Willsmithiraq]

Further tests, I've removed the ducting from the evap to eliminate that poissibility and it has made no difference either to the unit cycling on LP

[coolkid]

Hi Willsmithiraq,

have you added any additional pipe, in excess of what the unit is pre-charged for?

[lana]

Now try to close the TEV.
Close it and have a look at the suction pressure. When liquid is coming out of the evap then suction pressure goes down because there is not enough gas.
If you see no change in the pressure then the TEV has a problem.

Have patience this needs time.

Cheers

[lana]

Sorry forgot,

In what position did you install the TEV bulb?
It must be on 5 o'clock and completely insulated.

[Willsmithiraq]

The bulb is installed as per the Sporlan instructions at 4 'o' clock position and is fully insulated. How would I go about closing the valve? The exit of the evaporator is at -9 C, I have nothing to get the bulb any colder than that to shut it the valve down?

[Willsmithiraq]

Another point is that when the unit is run in heating, after a few minutes the unit trips on HP. This says to me that you are right Iana about the lack of evaporator capacity. As when in heating the undsersized coil cannot reject enough heat so it goes out on HP.

Does that make sense to you??

Will

[Brian_UK]

Just thinking out loud...

Is the evaporator piped up correctly?

Distributor fitted?, tube blocked with braze?

[DTLarca]

You haven't blocked off the external equaliser connection somehow? Too much brazing?

If the subcool is okay but the superheat none then surely the system is also overcharged?

[sedgy]

hi stanley park will, tell me ,on the evap , is the fan going the right way?
sedgy < oldham <

[Willsmithiraq]

The distributor came pre fitted to the unit, and when brazing in the components I had no trouble purging with nitro flowing through the evap and out the suction line.

Sedgy - The evap fan is running the correct way around.

[lana]

Hi there,

Is there a receiver?

If not then this could happen :

There is a blockage in liquid line somewhere (TEV,filter,tube,...). When in cooling mode then you get LP fault with high superheat. BUT you say you have no super heat. I am very suspicious about your super heat measurement :eek:. Do you have correct equipment ?
Now assuming this theory is correct then in the heating mode condenser (evap) tubes are filled with liquid and heat transfer area goes down therefore, HP fault.

What I suggest is you carefully measure the super heat as follows :
Connect a thermometer on the outlet tube of the evaporator. Connect your gages. Put the system in cooling mode and run it. Take the tube temperature with LP reading. With LP reading (g) go in the P-T chart for R410A and find the corresponding temperature. R410A has low glide so either temperature (dew , bubble) would be fine. Be careful if your chart is based on absolute pressure then you have to add atmospheric pressure to your reading.
T(tube) - Te = super heat
When you have correct super heat then we can find the fault.

BTW : it's LANA not Iana :off topic:
Cheers
LANA

[mad fridgie]

Is this design for high ambient conditions (both dry and wet bulb)
If so discharge pressure is low, and limited load on the evap, compounding the problem. Slow the cond fan down, if you can or block of some of the cond.
If your air on is 20C why do you want AC?
Also out door fan speed if running to fast could give you high suction pressures on heating.
Are you at altitude (up high)?

[Willsmithiraq]

Right then!

I spoke to the supplier who wanted to eliminate anything that I had installed on site ( drier, sight glass, txv and check valve at the evap end) and return the system to a pure heat pump. Which I did and pressure tested, vacced and switched on. And what a suprise within 30 seconds or so the system pressure rose to 600psi and then cutout!!

Lana, so I decided to investigate your theory about the blockage in the liquid line, so as much as I didn't want to again...I recovered the refrigerant and cut the pipes. I've taken everything apart and blown everthing out with nitrogen and it all seems clear, no restrictions?

Going back to my original figures maybe everybody has overlooked my readings?

Liquid line temp 31 C
After TXV -2C (minus 2C)
Exit evap -9 C (minus 9C)

I'm really struggling now to think of where this blockage could be.....or is it staring me in the face??

Cheers

Will

[lana]

Did you use an externally equilized TEV?

[Willsmithiraq]

Yes Lana the TEV is externally equalised and is connected to the evaporator outlet downstream of the TEV bulb.

[NoNickName]

You haven't blocked off the external equaliser connection somehow? Too much brazing?


That would be my first thought also.

[Willsmithiraq]

As I said in my previous post I've checked all of the conenctions as I had it all apart and checked the TXV too! Nothing, is it possible that the valve is oversized for the task? Unfortunately I think there is more than one problem with this system and trying to nail one down seems to be a nightmare!

[kg4yub]

just thinking out loud , could evap fan be put on motor shaft backwards ?

[Willsmithiraq]

just thinking out loud , could evap fan be put on motor shaft backwards ?

That's a fair shout and well worth a check, it is made in Italy this unit!!!!! :rolleyes: Will let you know what I find!!

Cheers

Will

[NoNickName]

Are you sure this unit is designed for cooling ambient air? Is it a fresh air unit? What is the design ambient temperature? I think that for your region, it could have been designed for 42°C ambient, and now it's working in ambient of 20° with a room of 20°C, so it's over cooling... and freezing over, of course.

[Gary]

Could some of the air be bypassing around the evap coil?

The evap air in/out says there is sufficient airflow, but everything else says not.

[Willsmithiraq]

It is a fresh air unit, I will have to speak to the designers about what the design parameters were and get back to you. But I see your line of thinking!! More stuff to check out tomorrow. We've been onto the manufactures today as well with the faults and hopefully should be getting some info back from them soon

Just quickly has anyone ever had any experience with these units? Made by "Ferroli" Italian firm.

Cheers

[Willsmithiraq]

Could some of the air be bypassing around the evap coil?

The evap air in/out says there is sufficient airflow, but everything else says not.

All the panels fit nice and snug on the air handling unit. No air leaks on the unit at all, and there is no place for it to bypass the coil as it's blocked off.

One thing that I have noticed is that you can easily open the inspection door to view the fan when the fan is running. The fan setup is 4420m3/h

All air handlers that I've worked on in the past are usually almost impossible to open when the fans are running.

[Willsmithiraq]

What do you make of the values of minus 2C entering the evap and minus 9C exitting the evap??

[Gary]

Another point is that when the unit is run in heating, after a few minutes the unit trips on HP. This says to me that you are right Iana about the lack of evaporator capacity. As when in heating the undsersized coil cannot reject enough heat so it goes out on HP.

Does that make sense to you??

Will

This also says air flow problems.

What were the air in/out temps in heat mode?

[Gary]

All the panels fit nice and snug on the air handling unit. No air leaks on the unit at all, and there is no place for it to bypass the coil as it's blocked off.

One thing that I have noticed is that you can easily open the inspection door to view the fan when the fan is running. The fan setup is 4420m3/h

All air handlers that I've worked on in the past are usually almost impossible to open when the fans are running.

This also points to airflow.

I'm assuming this is a squirrel cage fan. I'm wondering if the wheel might be installed backwards, backhanding the air as opposed to cupping it.

[Gary]

The evap delta-T is puzzling. Given an airflow problem, I would expect the evap air off temp to be much lower.

[Willsmithiraq]

I never managed to get to the point of taking temps in heating mode, as the unit trips out on HP within 20 seconds or so. All I can say is that in heating I've felt the heating TXV and there is definately temperature difference across it, also there is cold air coming out of the condensing unit.

As the evap is now the condsensor in heating with the lack of capacity the unit trips that quickly it's like a complete condensor fan failure situation.

[Willsmithiraq]

That was mentioned earlier in the thread about the cage being backwards on the shaft, it's definately something I'll be checking out tomorrow!!

[Gary]

Are you measuring the evap air in/out temps close to the coil?

[Willsmithiraq]

Are you measuring the evap air in/out temps close to the coil?

Yes, as close as I can get without opening the panels. One reading at the ambient air on side (500mm before coil) and one reading prbe inserted into the duct (700mm after coil).

I also double checked my temp probe with another to make sure it was up to scratch!

[Gary]

Is the evap coil frosting evenly?

I'm thinking the multi-circuit coil may have plugged distributor tubes, in effect short circuiting the coil.

[Gary]

Thinking pics might help.

[DTLarca]

The evap temperature after the TEV is -2°C but at the end of the evap is -10°C while the suction pressure is 70psi?

You don't say if the -2°C is after the distributor tubes but it sounds like the valve is so overfeeding the evaporator it is choking it and the temperature drop through it on the refrigerant side is only because there is a massive refrigerant pressure drop through the coil which under normal deed rates would not exist.

[Gary]

Is the TXV externally equalized? If so, is the bulb mounted before or after the equalizer tube?

[nevgee]

Hi guys,

Another one here thinking out aloud ;)

He has 8K super heat.
Suction pressure 50psig (3.5barg)
R410a sst = -17C
if he is reading -9C at evap outlet then he has 8K of super heat.
not large not small.

Lack of evap load / capacity.
Assuming everything is correct for the evaporator, ie right fan, etc, how do we know the evaporator has not been selected wrongly.
Maybe they've sent him the wrong coil? :mad:
In this case he will be waisting his time trying to resolve the issue.

So it might be worth the effort to double check the design parameters of the coil (evap) and the cond unit are matched.

[NoNickName]

Just quickly has anyone ever had any experience with these units? Made by "Ferroli" Italian firm.


Ferroli is one of the most reputed companies in the heating sector, located in NE-Italy, near Verona.
They don't have a grip on hvac in general as much as on heating, and I'm pretty sure they are not as proficient on fresh air systems as they are with gas furnaces, burners or fan coils.

[DTLarca]

Hi guys,

Another one here thinking out aloud ;)

He has 8K super heat.
Suction pressure 50psig (3.5barg)
R410a sst = -17C
if he is reading -9C at evap outlet then he has 8K of super heat.
not large not small.

Lack of evap load / capacity.
Assuming everything is correct for the evaporator, ie right fan, etc, how do we know the evaporator has not been selected wrongly.
Maybe they've sent him the wrong coil? :mad:
In this case he will be waisting his time trying to resolve the issue.

So it might be worth the effort to double check the design parameters of the coil (evap) and the cond unit are matched.

If you are right in choosing the -9°C as matched to 50psi rather than 70psi then with the superheat being okayish it seems the TEV and compressor are over sized for the evaporator.

Or the evaporator is sized for much warmer outdoor conditions than exist now and during these conditions some sort of compressor/evaporator capacity control is required.

EPR alone if the compressor can cope with the lower suction pressures otherwise hotgas and liquid injection after the EPR. Or simply hotgas after the TEV.

Head pressure control would then be needed and this will also reduce the compressor capacity bringing the superheat down a few degrees.

[nevgee]

I would go along with that

[Gary]

I would agree that some sort of capacity control is needed, but given the current conditions, the low side pressure should be much higher.

The delta-T indicates sufficient airflow.

It seems like there is insufficient heat transfer from the air to the refrigerant.

[DTLarca]

I would agree that some sort of capacity control is needed, but given the current conditions, the low side pressure should be much higher.

The delta-T indicates sufficient airflow.

It seems like there is insufficient heat transfer from the air to the refrigerant.

Do you think the delta-T with a fresh air system in Afghanistan summers would be similar a mid US comfort cooling system? The humidities in Afghanistan are also low, I think, so it could be this coil is sized for 40°C air on temps. As with the condenser.

[nevgee]

He still needs to check that the unit is sized for a balance with the condensing unit ... what ever the design parameters, and then go forward with a plan or further diagnostics.

[r.bartlett]

Like a few here my hunch say's air flow. If you can open the door to the fan easily that means the air isn't going anywhere.

Are there any dampers (fire or otherwise) upstream of the unit?

Open the door which is past the fan. Can you then open the fan access door?

It's possible the TD figure is a red herring? ...

As Gary say's post pictures

[bill1983]

my thoughts to the letter mr bartlett! investigate airflow due to being able to open door easily. heat transfer IS airflow. without it nothing else will matter. sort it and check your readings again.

[DTLarca]

Like a few here my hunch say's air flow. If you can open the door to the fan easily that means the air isn't going anywhere.

Are there any dampers (fire or otherwise) upstream of the unit?

Open the door which is past the fan. Can you then open the fan access door?

It's possible the TD figure is a red herring? ...

As Gary say's post pictures

I think your hunch is not without substance. The numbers do seem to be all over the place. As if there could be more than just one component wrongly selected.

If the evaporating pressure is, as nevgee says it is, at 50psi, then would the system capacity rise to (1.03)^19 = 175% of its current capacity when the evaporating temperature rises 19 from -17°C to 2°C? That would mean the system capacity drops to (0.99)^20 x 175 = 143% when the ambient rises to 40°C.

The delta-T, as Gary calls it, would increase from 11 to 15.7 resulting in a fresh air supply temperature of 24.3°C.

Does this support the idea that the air flow could be less than design? Equally it could support a claim that the air flow is higher than design?

[DTLarca]

my thoughts to the letter mr bartlett! investigate airflow due to being able to open door easily. heat transfer IS airflow. without it nothing else will matter. sort it and check your readings again.

But would you not expect the superheat to also drop below the ideal. At the moment it seems to be above.

[DTLarca]

But would you not expect the superheat to also drop below the ideal. At the moment it seems to be above.

Step 1: Achieve design head pressure. What then does the superheat do?

[DTLarca]

Are you sure this unit is designed for cooling ambient air? Is it a fresh air unit? What is the design ambient temperature? I think that for your region, it could have been designed for 42°C ambient, and now it's working in ambient of 20° with a room of 20°C, so it's over cooling... and freezing over, of course.

I just noticed your post. You are probably right.

The subcool will increase as the ambient rises to design. It usually then decreases again when ambient exceeds design.

The superheat is high because the head pressure is too low but the superheat is also not so high because the evaporator air on temperature is also low. Raise the head pressure to design levels and we will see the superheat crash. This would confirm a low load condition which would be either because of low air flows or low air temperatures or both.

[Willsmithiraq]

Guys,

Thanks for all the info you've replied, I shall be investigating the airflow over the next few days and as Gary said will get back to you all with some pictures, which may help clear this problem up.

Really appreciate all your posts, as it's not fun being stuck on your own out here with nobody to help you!! :D

[mad fridgie]

There is nothing wrong with operation of the refrigerant plant per say, TXV is doing what it should do. Your problem does not lie here. Because you have extreme problems with both heat and cooling, this does indicate either lack of air flow (for what ever reason), or the incorrect coil selection.
So lets look athe air flow first.
Check fan moter rotation against blade/wheel rotation, fix if wrong!
Test either way.
Remove inlet and outlet duct from indoor coil, no air restrictions, all works well, then theres lies your problem " Ducting",
If still a problem (in heat and cooling)
then manufactures have F***** UP, wrong coil/fan configuration.
After what NNN said about the manufacturer, I would not surpise me if they have designed the coil based upon steam or hot water!
Remember when testing to test both heat and cool (lower suction pressure would be expexted just because you load is quite small any way)

[DTLarca]

If the system is for fresh air supply only then you might find the compressor circuit should not be running below say 28°C air on temps.

The TEV capacity will increase as the ambient increases even though when the ambient increases so does the air on to the evaporator, because they are the same thing. This is because the pressure differential across the from high to low will increase with the curvature of the saturation curve.

So my bet is that head pressure control with desuperheated hot gas injection will be required. If there is no side injection point on the TEV distributor for the hotgas then injecting hot gas into the suction will probably be the best solution.

The superheat being 8K at the current conditions indicates a higher than required air flow exists right now. So the most likely problem is simply a low ambient and low load combination.

[NoNickName]

If there is no side injection point on the TEV distributor for the hotgas then injecting hot gas into the suction will probably be the best solution.


That way would not prevent the coil from freezing, but only the compressor. I would suggest to inject hot gas between the TEV and evaporating coil.

[DTLarca]

That way would not prevent the coil from freezing, but only the compressor. I would suggest to inject hot gas between the TEV and evaporating coil.

It's not the hotness of the hotgas that prevents freezing. It's that it raises the saturated suction pressure. So injecting into either point works. After the TEV just improves oil return from there.

But including an EPR along with head pressure control and desuperheated hot gas injection would be good too.

Usually the distributor tubes into the evaporator have to be increased a size when hot gas is injected after the TEV.

[NoNickName]

So injecting into either point works.


mmmmhhh what about the equilibrium line and the bulb in respect to the injection point?

[DTLarca]

Here are two illustration Courtesy of Sporlan (Parker).

[NoNickName]

Well, so be it.
I still think the injection point would be better placed ahead of the evaporator, but it is MHO.

[DTLarca]

Well, so be it.
I still think the injection point would be better placed ahead of the evaporator, but it is MHO.

I agree. This is the preferred method if the evaporator is located near the condenser as in packaged equipment.

But if the evaporator is a distance from the condenser then there can be condensation along the the longer hot gas injection run. The effect is worse if the hot gas valve is located near the evaporator but can also be a problem when it is installed nearer the condenser. if it has to be done then nearer the condenser is preferable.

[r.bartlett]

Well, so be it.
I still think the injection point would be better placed ahead of the evaporator, but it is MHO.

This would be my prefered methos as it gives the hotgas chance to cool down. I have seen many with the HG line at the condenser (for cost) which causes high suction temps at the compressor

[DTLarca]

This would be my prefered methos as it gives the hotgas chance to cool down. I have seen many with the HG line at the condenser (for cost) which causes high suction temps at the compressor

When we're injecting hot gas into the suction the only concern regarding temperatures is superheated discharge temperature. Having a warmer suction vapour means it is more rarefied which means the mass flow is also reduced which helps keep saturated suction temperatures up. Comressor cooling is more dependenat on refrigerant mass flow than on refrigerant temperature. Many rotary type compressors actually have their motors located in the discharge stream.

When we use an EPR we are injecting hot gas to maintain compressor cooling by maintaining mass flow through the compressor.

The desuperheating valve is adjusted, superheat, to maintain safe superheated discharge temperatures. This is easily achieved with any of the possible configurations.

The other advantage with injecting hot gas after the TEV is good refrigerant distribution is kept up even at the low load conditions.

[Gary]

I never managed to get to the point of taking temps in heating mode, as the unit trips out on HP within 20 seconds or so. All I can say is that in heating I've felt the heating TXV and there is definately temperature difference across it, also there is cold air coming out of the condensing unit.

As the evap is now the condsensor in heating with the lack of capacity the unit trips that quickly it's like a complete condensor fan failure situation.

I'm thinking there might be an important clue here. For the unit to trip on HP that quickly, there would have to be zero airflow... or perhaps a restriction between the compressor discharge and the (indoor) condenser coil. Maybe at the coil connection?

Since this line is the suction line in cooling mode, a restriction at the coil connection would explain everything.

[Willsmithiraq]

Gary,

Not sure if I've previously said in this thread. But after the problems I had I cut both connections to the evap and blew nitrogen through from either direction at high pressure. This didn't appear to dislodge anything from the evap coil.

Going back to a comment you made earlier about one of the legs of the distributor being blocked. When the unit was operational, I had my head inside the unit and felt each leg and they "appeared" to be of equal temp going into the evap (something that I will get a probe on next time I get to the unit). Also the ice that was forming seemed to be forming equally across the coil.

[Gary]

Suction 70 psi going down to 50 psi which is the cutout
Discharge 285 psi

Liquid line temp at TXV 31 C
After TXV -2 C
Exit evap - 9 C

Subcooling 4 C
Superheat - None??

Air on cond - 20 C
Air off cond - 36 C

Air On Evap - 20 C
Air Off Evap - 9 C


Your use of minus signs is confusing me... beyond my usual level of confusion. :confused:

[Gary]

I'm wondering how the air temp leaving a frosted coil can possibly be 9C?

[Willsmithiraq]

Your use of minus signs is confusing me... beyond my usual level of confusion. :confused:

Originally Posted by Willsmithiraq http://www.refrigeration-engineer.com/forums/images/VA_RE/buttons/viewpost.gif (http://www.refrigeration-engineer.com/forums/showthread.php?p=208374#post208374)
Suction 70 psi going down to 50 psi which is the cutout
Discharge 285 psi

Liquid line temp at TXV 31 C
After TXV - 2 C (minus 2C)
Exit evap - 9 C (minus 9C)

Subcooling 4 C
Superheat - 1K @ 70 psi - 8K @ 50 psi

Air on cond + 20 C
Air off cond + 36 C

Air On Evap + 20 C
Air Off Evap + 9 C

Sorry!!! Hope this clears it up!!:o

[Gary]

In any case, the fact that the coil frosted evenly is proof positive that the air as it immediately leaves the coil is below 0C, which means this is very definitely an airflow problem.

[DTLarca]

In any case, the fact that the coil frosted evenly is proof positive that the air as it immediately leaves the coil is below 0C, which means this is very definitely an airflow problem.


In the last month I have designed two systems each with an effective coil dew point temperature between 7°C and 9°C. The air flow for the first system, m³/kW, was 4 times that for the second system. The first system has a fresh air requirement for 120 people in a confined space and the second gave no fresh air. To meet the cooling loads in the first instance the air only needed to be cooled from 24°C to 21°C. The second system was designed for air on at 22°C and off at 10°C. The first system, even though the air was only being cooled from 24°C to 21°C, did anyhow have a higher sensible heat ratio - it had a higher moisture removal per kW than the second system.

Fresh air systems do not normally have the same Delta-T vs. Approach relationships as comfort cooling.

[DTLarca]

[quote=DTLarca;208986]The first system, even though the air was only being cooled from 24°C to 21°C, did anyhow have a higher sensible heat ratio - it had a higher moisture removal per kW than the second system.[quote]

Sorry - big mistake there - lower sensible heat ratio - not higher - the 24°C -> 21°C fresh air system with fresh air pre-cooling by enhalpy exchanger and pre-cooling coil had a lower sensible heat ratio at the final cooling coil than the comfort coiling system.

[Gary]

In the last month I have designed two systems each with an effective coil dew point temperature between 7°C and 9°C. The air flow for the first system, m³/kW, was 4 times that for the second system. The first system has a fresh air requirement for 120 people in a confined space and the second gave no fresh air. To meet the cooling loads in the first instance the air only needed to be cooled from 24°C to 21°C. The second system was designed for air on at 22°C and off at 10°C. The first system, even though the air was only being cooled from 24°C to 21°C, did anyhow have a higher sensible heat ratio - it had a higher moisture removal per kW than the second system.

Fresh air systems do not normally have the same Delta-T vs. Approach relationships as comfort cooling.

Sorry, but I'm just not understanding your point. :confused:

[Gary]

[quote=DTLarca;208986]The first system, even though the air was only being cooled from 24°C to 21°C, did anyhow have a higher sensible heat ratio - it had a higher moisture removal per kW than the second system.[quote]

Sorry - big mistake there - lower sensible heat ratio - not higher - the 24°C -> 21°C fresh air system with fresh air pre-cooling by enhalpy exchanger and pre-cooling coil had a lower sensible heat ratio at the final cooling coil than the comfort coiling system.

And I still don't get it. :confused:

[DTLarca]

In any case, the fact that the coil frosted evenly is proof positive that the air as it immediately leaves the coil is below 0C, which means this is very definitely an airflow problem.

What I am saying is that for my high fresh air percentage system that was designed with an air on temperature of 24°C and an air off temperature of 21°C and what we call an apparatus dew point temperature of 7°C having a SHR of 0.68 I will have a frosty coil when my return air temperature drops to 14°C at which point my air off temperature will be 12.2°C. My air off temperature does not have to also be below freezing for the coil to freeze.

The bypass factor means there is also a contact factor. The contact factor is the portion of the air volume that leaves at coil temperature. The bypass factor is the portion that leaves, after having made no contact with the coil, remaining at return air temperature. These two air volumes mix leaving the coil to give you your air off temperature always somewhere above the coil temperature.

Now, if you had 100% contact then off course the air would leave at exactly the same temperature as is the coil. But of all the system types one can design fresh air system possibly have the highest by pass factors or the lowest contact factors.

I hope my point is clearer now :)

[Gary]

Okay7... I understand this. Similar to a face/bypass system. That would be an enormous bypass factor... and that's why I questioned whether there might be bypass around the coil earlier.

[Gary]

So... if I am understanding you correctly, possibly the coil has a large bypass factor and is working properly... doing exactly what it is designed to do... shutting down the compressor in mild weather and just bringing in fresh air.

This brings us to the heat mode problem. The large bypass factor is going to be a big problem in heat mode.

[DTLarca]

Okay7... I understand this. Similar to a face/bypass system. That would be an enormous bypass factor... and that's why I questioned whether there might be bypass around the coil earlier.

The bypass factor in this case was (21-7)/(24-7) = 0.82 or 82% of the air makes no contact with the coil.

This is typical of the school ventilation systems we do - particularly in the new and ever more popular Academies.

[lma]

Your system is designed for R410a... try increasing suction pressure to between 100-110 psi .. you head pressure should be .. in the region of 400 - 420 psig ... see if this achieves desired effect

[Gary]

The bypass factor in this case was (21-7)/(24-7) = 0.82 or 82% of the air makes no contact with the coil.

This is typical of the school ventilation systems we do - particularly in the new and ever more popular Academies.

Interesting... a built in bypass... clever :)

[Gary]

Hmmm... if we can confirm that the airflow is correct and as DTLarca suggests, this is a high bypass factor coil (fin spacing, number of rows?), then the only way this can be made to run in cooling mode in mild weather would be to raise high side pressure (and therefore low side pressure) by reducing airflow through the outdoor unit fan.

In order for it to work properly in heat mode, we would need to drop the low side pressure (and therefore the high side pressure) by again reducing the airflow through the outdoor unit fan.

Sure would be nice to have the design information on this system.

[DTLarca]

So... if I am understanding you correctly, possibly the coil has a large bypass factor and is working properly... doing exactly what it is designed to do... shutting down the compressor in mild weather and just bringing in fresh air.

That's it :)


This brings us to the heat mode problem. The large bypass factor is going to be a big problem in heat mode.

It may be designed to deliver heat to 0°C fresh air when taking heat from 0°C ambient air. In which case giving it 20°C and 20°C as is happening now would be the equivalent to giving a normal home AC heat pump system 40°C air on indoors with and outdoor temperature of 25°C. Of course the system will trip on head pressure - it has no capacity control.

The outdoor fan needs speed control for these conditions both for head pressure control in cooling and then for suction pressure control in heating.

Or simply choose to neither heat nor cool in these conditions but rather up or below at the more extreme conditions.

[Gary]

In the meantime, until proven otherwise, I'm sticking with the insufficient airflow theory. :)

[DTLarca]

In the meantime, until proven otherwise, I'm sticking with the insufficient airflow theory. :)

The odds are against you :)

The superheat, the evaporator approach and the subcool should all be low if it was an evaporator air flow problem :cool:

[Gary]

The odds are against you :)

The superheat, the evaporator approach and the subcool should all be low if it was an evaporator air flow problem :cool:

Also, the outdoor (condenser) TD indicates a normal load. :)

I may come around to your way of thinking, yet. Maybe knowing the fin spacing and number of rows will settle this.

[DTLarca]

Also, the outdoor TD indicates a normal load. :)

Good point - I forgot all about the condenser situation apart from the subcool.

But hang on - 285psi is about 33.5°C saturated condensing temperature. The air leaving is warmer at 36°C? They probably weren't taken at the same time but if I had to go on those readings I would say the condenser air flow is too low by far. The leaving air is being exposed to the superheated tube rows long enough to leave above saturated condensing temperature.

The TD can be brought down significantly with an increase is air flow. The subcool would increase slightly too as we turn more vapour to liquid with the increased air flow.



I may come around to your way of thinking, yet. Maybe knowing the fin spacing and number of rows will settle this.

All we need is the dry and wet bulb temperatures of the air on and off and we can determine the apparatus dew point temperature and then the current bypass factor.

[mikeref]

There is nothing wrong with operation of the refrigerant plant per say, TXV is doing what it should do. Your problem does not lie here. Because you have extreme problems with both heat and cooling, this does indicate either lack of air flow (for what ever reason), or the incorrect coil selection.
So lets look athe air flow first.
Check fan moter rotation against blade/wheel rotation, fix if wrong!
Test either way.
Remove inlet and outlet duct from indoor coil, no air restrictions, all works well, then theres lies your problem " Ducting",
If still a problem (in heat and cooling)
then manufactures have F***** UP, wrong coil/fan configuration.
After what NNN said about the manufacturer, I would not surpise me if they have designed the coil based upon steam or hot water!
Remember when testing to test both heat and cool (lower suction pressure would be expexted just because you load is quite small any way)
May i draw your attention back to this post. Would it not be reasonable to suggest the lack of air flow theory is due to restrictive ductwork or shortage of registers? The air volume has been given but not measured at the registers to confirm flow rate..

[Gary]

I consider delta-T to be the best indicator of airflow. In this case 36C-20C=16K dT. I would consider this (borderline) sufficient.

The cond TD would be 33.5C-20C=13.5K TD, which would indicate a normal load, given sufficient airflow.

As you point out, the SCT should be higher than leaving air. This could be due to the timing of the measurements or instrument error.

In any case, if there is insufficient heat load picked up on the low side, we should expect insufficient heat load to be rejected on the high side (low TD).

[Gary]

As you point out, the SCT should be higher than leaving air. This could be due to the timing of the measurements or instrument error.


Gauge calibration is especially difficult in moutainous regions as elevation has a profound affect. One good way to calibrate is to strap a temp sensor to the side of a refrigerant jug and calibrate the gauges to the temp indicated.

Zeroing the gauges is only accurate at sea level.

[NoNickName]

The deltaT or airflow theory is slippery IMHO. The acceptable range of both can only be demonstrated against the actual front surface and rows of the exchange coil. Without actual data sheets and coil selection sheets it would be impossible to determine if that is the case.
I see the experience would lead elsewhere, but I think we have to stick to what we know.
In the published data of the OP, the only anomaly, again IMHO, is the evaporating temperature.
For a A/C system, a negative evaporating temperature is not acceptable, everything else is disputable.
A negative evaporating temperature can only be caused by
1) insufficient exchange surface.
2) excess capacity

1) would be systematic and unrepairable. It would be a design fault.
2) can be caused by a number of reason, that have been showed in this same thread.

I would start from there for a proper diagnosys.

[nevgee]

I'll eat my hat on this one.... while you're chugging about bypass factors and turbulent flows in heat exchange processes, this poor guy is wanting a practical solution to a real problem. Pontificating and feather fluffing doesn't help him. :mad:

Keeping the theory to the class room ..... I think he needs to take full details of the evaporator, rows, tubes, fpi, face area and go back to the manufacturer to get them to double check he has a matched set of condensing unit and evaporator.
Either the cu has too high a capacity for the job or the evap is too small a duty for the cond unit.

If it turns out the evap is too small then most likel y he will need to add some form of capacity control. Hot gas by pass being one option to maintain a higher back pressure. Injection into the inlet of the evap coil being a better option but does not exclude the injection at the evap outlet. both ways work well if set up properly.

However, there are other complications if he is trying to use this system as a heat pump /reverse cycle arrangement. other considerations need to be thought thru.

He should really take up the fight with the supplier/ manufacturer who really are responsible for the design and mods that may be needed to correct the problem.

OK guys ...... go back to the theory . . battle on! ;)

[mad fridgie]

First thing to remember is that faults occur in both Cooling and heating, all idications is that there is controlled flow of the refrigerant.
measured temperature differences of the air (indoor) maybe mis leading, if the coil temp is -9C (SST) then ice formation will occur on the fins stopping heat transfer futher, showing a higher air outlet temperature than what would be expected.
Of course capacity control maybe required if the unit is designed for high ambient conditions, but this not where the present problem lies. HEATING fails within 5 minutes.
So what dos this show incorrect airflow or incorrect indoor design (this being the case I bet the coil is only and 0ne or two row coil, as designed for high temperature working mediums)

[mad fridgie]

Nevgee, is sort of right, but prior to going to the manufacture, you need test the unit under free airflow conditions, remove any installation potential problems. DIS CONNECT DUCTING

[mikeref]

Some pics would go down well. What about positive pressure in the kitchen area?

[Gary]

Some pics would go down well. What about positive pressure in the kitchen area?

Good point. If there is no means of exhausting kitchen air then the flow will be reduced... like blowing into a bottle.

[Gary]

Call the manufacturer?... where's the fun in that?

[nevgee]

Good point. If there is no means of exhausting kitchen air then the flow will be reduced... like blowing into a bottle.




Most likely their doors don't fit too well and I recon the're will be loads of gaps and spaces where air will pass thru, assuming the ****roaches haven't occupied them all :D

[DTLarca]

Gauge calibration is especially difficult in moutainous regions as elevation has a profound affect. One good way to calibrate is to strap a temp sensor to the side of a refrigerant jug and calibrate the gauges to the temp indicated.

Zeroing the gauges is only accurate at sea level.

Great point. At higher altitudes the superheat readings are lower than actual and the subcool readings are higher than actual.

[mad fridgie]

Great point. At higher altitudes the superheat readings are lower than actual and the subcool readings are higher than actual.
Bull shyte, temperatures do not change with altitude, what changes is gauge calibration, which is pressure. Alltitude also effects mass flow of given from a fan, and heat transfer coiefficients on heat transfer. There is no problem in this thread with refrigerant control!!!!

[nevgee]

Call the manufacturer?... where's the fun in that?


Well perhaps you're right ;) ... but this guy is on a commercial contract ... he has to get a system running, keep client happy and a reputation to maintain. If he fixes this problem, by any means, the client will be pleased. If on the other hand he pisses about fannying over theoretical issues of flow and bypass factors etc, the client ain't going to be very happy.

In a real world Gary, the pressure is on when some one has paid for a system and it isn't working as specified. They don't care about theories they want results, now , not whenever.

I feel for this guy, he needs some help to get him or the system out of the mire. He'll be reading all of these posts and be getting lost with the runaround, he needs to be offered sound practical advise that he can act on. If he were in an R & D shop then it would be different I'm sure. :)

[nevgee]

Bull shyte, temperatures do not change with altitude, what changes is gauge calibration, which is pressure. Alltitude also effects mass flow of given from a fan, and heat transfer coiefficients on heat transfer. There is no problem in this thread with refrigerant control!!!!


well said ;)

[nevgee]

..... assuming the ****roaches haven't occupied them all :D


Roaches? Spliffs? Doobies? I am suprised ;)

[DTLarca]

I consider delta-T to be the best indicator of airflow. In this case 36C-20C=16K dT. I would consider this (borderline) sufficient.

The cond TD would be 33.5C-20C=13.5K TD, which would indicate a normal load, given sufficient airflow.

As you point out, the SCT should be higher than leaving air. This could be due to the timing of the measurements or instrument error.

In any case, if there is insufficient heat load picked up on the low side, we should expect insufficient heat load to be rejected on the high side (low TD).

At the moment since the condenser's air is leaving at about the same temperature as the saturated condensing temperature we would not know how much under normal the volume flow is. That's m³/kW norms versus this system.

Much of the confusion here comes about because this system is for a fresh air application and is a heat pump.

I have attached an image of the sort of configuration we normally use for 100% fresh air systems. The condenser is located in the exhaust air stream. There is also an adiabatic heat transfer plate heat exchanger...

Oops, suddenly I am unable to upload images from my computer? The facility has gone blank?

[mikeref]

Further tests, I've removed the ducting from the evap to eliminate that poissibility and it has made no difference either to the unit cycling on LP
This post from a few days ago, narrows down possibilities.

[DTLarca]

Bull shyte, temperatures do not change with altitude, what changes is gauge calibration, which is pressure. Alltitude also effects mass flow of given from a fan, and heat transfer coiefficients on heat transfer. There is no problem in this thread with refrigerant control!!!!

The temperatures do not change - the readings do. Subcool and superheat readings change.

A bourdon gauage calibrated to 0kpa at sea level will still show 0kpa if taken to the moon. On the moon then the superheat readings will appear negative when in fact positive and the subcool readings will be fantastically high when in fact normal.

[mad fridgie]

This post from a few days ago, narrows down possibilities.
Missed that one Mikeref, well spotted!
Have a doughnut!

[Gary]

In a real world Gary, the pressure is on when some one has paid for a system and it isn't working as specified. They don't care about theories they want results, now , not whenever.


I was a hands-on service tech for 40 years. I know all about the real world. In the real world, the more you learn, the better you serve your customers in the future.

[DTLarca]

Well perhaps you're right ;) ... but this guy is on a commercial contract ... he has to get a system running, keep client happy and a reputation to maintain. If he fixes this problem, by any means, the client will be pleased. If on the other hand he pisses about fannying over theoretical issues of flow and bypass factors etc, the client ain't going to be very happy.

In a real world Gary, the pressure is on when some one has paid for a system and it isn't working as specified. They don't care about theories they want results, now , not whenever.

I feel for this guy, he needs some help to get him or the system out of the mire. He'll be reading all of these posts and be getting lost with the runaround, he needs to be offered sound practical advise that he can act on. If he were in an R & D shop then it would be different I'm sure. :)

This is basic commissioning knowledge. If you want to get into the design then we can go there but I think that would be unnecessary considering the scope of practicalities here.

Gary asked about the bypass factor principles I mentioned - not the original poster. So the answers were not addressed to the original poster - only to Gary. The comments about this being a fresh air application possibly being asked to operate out of range were aimed at the original poster and all other posters in general.

[mad fridgie]

The temperatures do not change - the readings do. Subcool and superheat readings change.

A bourdon gauage calibrated to 0kpa at sea level will still show 0kpa if taken to the moon. On the moon then the superheat readings will appear negative when in fact positive and the subcool readings will be fantastically high when in fact normal.
Guage surrounding pressure plus gauge mechanical pressure equal calibriation point, change surrounding pressure or mechanical pressure, calibriation point changes. When certifying gauges you test in a fixed pressure test chamber, a pressure over absolute vacuum, not a pressure over atmospheric conditions.
Why the surrounding pressure changes the stesses on the mechincal parts of a gauge

[mad fridgie]

I think we should move on and just help the OP with his problem
I think to make thing clear, we all need to know what excactly is his system.
Conditioned Air Flow
this comes from outside, inside or a mix,
it passes through a filter, heatexchanger, fan widget or what ever.
just a true description of what the process is. (as it would seem that we all have different ideas of what we are talking about, thus are giving different solutions based upon what we think we are dealing with) I think once this done we should all be singing on the same song sheet!

[nevgee]

This is basic commissioning knowledge. If you want to get into the design then we can go there but I think that would be unnecessary considering the scope of practicalities here.

Gary asked about the bypass factor principles I mentioned - not the original poster. So the answers were not addressed to the original poster - only to Gary. The comments about this being a fresh air application possibly being asked to operate out of range were aimed at the original poster and all other posters in general.


Going into the design principles would be ok for me and probably be more helpful, hence my reasoning over the style and build of the coil block. I couldn't see how bypass factors could have anything to do with basic commissioning! They are elements of design not commissioning. I doubt there are many peeps on here who would have the experience of designing air coils from basics, without a pc at hand.

I wasn't having a go at anyone ... just pointing out the main thread.
:)

[DTLarca]

Guage surrounding pressure plus gauge mechanical pressure equal calibriation point, change surrounding pressure or mechanical pressure, calibriation point changes. When certifying gauges you test in a fixed pressure test chamber, a pressure over absolute vacuum, not a pressure over atmospheric conditions.
Why the surrounding pressure changes the stesses on the mechincal parts of a gauge

In the field a digital micron gauge can tell you your altitude.

It can tell you also if your vac pump is good. If it is good then you can use it to calibrate your service gauges for altitude. Pull a vac on the gauges to the best your pump can get then set your gauges to show absolute vacuum. When disconnected they will rise to give you a better indication of the actual atmospheric pressure. Reconnect them to any system you were analysing and suddenly you'll see the actual superheat is higher than you read before and the actual subcool is lower than you read before.

Do this to systems in Mexico or Johannesburg and adjust the superheat to a true design superheat and you will gain perhaps 10% capacity on the system.

[DTLarca]

Going into the design principles would be ok for me and probably be more helpful, hence my reasoning over the style and build of the coil block. I couldn't see how bypass factors could have anything to do with basic commissioning! They are elements of design not commissioning. I doubt there are many peeps on here who would have the experience of designing air coils from basics, without a pc at hand.

I wasn't having a go at anyone ... just pointing out the main thread.
:)

No worries - but commissioning engineers must get the right SHR at the right total duty. For this they must understand the relationship between ADP and BPF. This is for custom build AHU's. For catalog AHU's only external static pressure and distribution balance is of concern. Standard AHU's have fans, motors and pulleys closely selected without much tolerance. Custom build AHU's these days have motors oversized by perhaps 40% with VFD's for RPM fine tuning according to ADP, SHR and BPF.

[mikeref]

Going over this thread from the start, there has been reference to the distributor piping, but i don't recall temperature readings at the individual circuit outlets to the collector. Would there be a chance the spider is incorrectly piped or some of the circuits have been shorted, or if the distributer is biased to only a few circuits? What about the distance between expansion valve and distributer?

[nevgee]

No worries - but commissioning engineers must get the right SHR at the right total duty. For this they must understand the relationship between ADP and BPF. This is for custom build AHU's. For catalog AHU's only external static pressure and distribution balance is of concern. Standard AHU's have fans, motors and pulleys closely selected without much tolerance. Custom build AHU's these days have motors oversized by perhaps 40% with VFD's for RPM fine tuning according to ADP, SHR and BPF.
:off topic:
Sensible Heat Ratio is preset at design given specific design parameters. Aparatus Dew Point and ByPass Factors are also predefined at design. I can't see how a commissioning Engineer is able to make any corrections to these factors when he is most like never to achieve designg conditions at all. I would find it very unusual that any one would have the luxury and satisfaction of designing an AHU system with ducting etc and for it to drop into a design performance for commissioning purposes. In a real world it never happens. There are many peeps who sit at their drwng brds believing that the world is perfectly round ...well it surely isn't and never will be. There is a great difference between design practice and the realms of commissioning and the reality of having to instal a system that wasn't thought thru properly. :off topic:

[DTLarca]

:off topic:
Sensible Heat Ratio is preset at design given specific design parameters. Aparatus Dew Point and ByPass Factors are also predefined at design. I can't see how a commissioning Engineer is able to make any corrections to these factors when he is most like never to achieve designg conditions at all. I would find it very unusual that any one would have the luxury and satisfaction of designing an AHU system with ducting etc and for it to drop into a design performance for commissioning purposes. In a real world it never happens. There are many peeps who sit at their drwng brds believing that the world is perfectly round ...well it surely isn't and never will be. There is a great difference between design practice and the realms of commissioning and the reality of having to instal a system that wasn't thought thru properly. :off topic:
Nevgee, if you and I were standing in front of an ahu that was not achieving the correct SHR, say the SHR was too high, what would be on your short list of things to check or adjust if you were about to turn around and give me suggestions?

[Gary]

Nevgee, if you and I were standing in front of an ahu that was not achieving the correct SHR, say the SHR was too high, what would be on your short list of things to check or adjust if you were about to turn around and give me suggestions?

Is there a neon sign on the side of the AHU that says, "My SHR is too high"?

[DTLarca]

Is there a neon sign on the side of the AHU that says, "My SHR is too high"?

Pretty much though actually a mini LCD indication ;)

[DTLarca]

Is there a neon sign on the side of the AHU that says, "My SHR is too high"?

Consider it this way, Gary.

You are standing between two AHU's. One has a return of 22 and a supply of 12 while the other a return of 24 and a supply of 21.

For a given deviation in leaving air temperature from design by say 0.2K which one is further off the SHR mark? The answer comes to mind instantaneously - yes?

[Gary]

Pretty much though actually a mini LCD indication ;)

That's what I get for retiring... they go and change everything.

I would take that to mean the humidity was too high, make sure everything is operating properly, then drop the air off temp (reduce airflow) just enough to get the RH where I want it.

In 40 years, I never once checked the SHR... or even cared about the SHR.

[nevgee]

Ok so I go thru the trouble of measuring everything and discover the SHR is wrong ... by how much has it to be out before I care? The ambient conditions are likely to change before I get the chance to correct my offsets. If its for comfort cooling why is there a problem if its not 0.7 or 0.75 or 0.8 ... who would bother?
Who would notice that the air is being treated in a slightly different way. the paper in the photo copier may not pass thru as smoothly .. some one may notice a little static or not ... I can't see why you are so "focussed" on this subject.

I've been in this industry a few yrs and have never heard anyone show so much passion for SHR ..... I am foncused. :confused:

[nevgee]

That's what I get for retiring... they go and change everything.


In 40 years, I never once checked the SHR... or even cared about the SHR.

Gary, I couldn't agree more with you on this one.

[Gary]

From a design/component sizing point of view, the SHR is important, but irrelevant to comissioning/servicing.

To my mind SHR is beside the point, RH is the point.

[mad fridgie]

SHR, has only reference to performance, if you have the design reference point to start with. I think someone has only ever read design books. If your air is vey dry, then the SHR will be high, if the air is humid, then then it will be low, what is important is the quality of the air leaving the ahu, the SHR% has no relevence to anything. It just a calculated number.

[nevgee]

Nevgee, if you and I were standing in front of an ahu that was not achieving the correct SHR, say the SHR was too high, what would be on your short list of things to check or adjust if you were about to turn around and give me suggestions?


You buying coffee or me? :D

[DTLarca]

Ok so I go thru the trouble of measuring everything and discover the SHR is wrong ... by how much has it to be out before I care? The ambient conditions are likely to change before I get the chance to correct my offsets. If its for comfort cooling why is there a problem if its not 0.7 or 0.75 or 0.8 ... who would bother?
Who would notice that the air is being treated in a slightly different way. the paper in the photo copier may not pass thru as smoothly .. some one may notice a little static or not ... I can't see why you are so "focussed" on this subject.

I've been in this industry a few yrs and have never heard anyone show so much passion for SHR ..... I am foncused. :confused:

nevgee, human comfort is first of all mostly effected by radiant temperatures and in particular radiant temperature asymmetries, secondly by dry bulb temperatures, thirdly by drafts, fourthly by discrepancies between neck and ankles greater than 3K and down the list we eventually come to humidity. this tells us SHR is actually not so important with everyday comfort cooling as compared to say the processing of drug powders or preventing the ink on the labels on Darwins specimen bottles at the Natural History Museum from running.

However, particularly for schools, where 3 litres per second per person is considered satisfactory in the UK - compare that to 10 l/s for office staff - at least it is over the 1 litre per second required for CO2 management, there is the tendency for humidities to hover up around the higher boundaries of the comfort envelope at 70%, from time to time and with a custom built AHU providing as high as possible a SHR for energy savings you are likely to depart from the limits ensuring comfort and health.

Operating SHR is, among a few other things amounting to mere synonyms, the line between return air dry and wet coordinates and ADP. ADP is discovered by extending a line from there on through leaving air dry and wet coordinates up to the saturation line. For every set of return air coordinates there is one and only one ADP that will give you the desired SHR. Control ADP and you control SHR.

[Gary]

Mmmmm... did someone say "Coffee"?

[nevgee]

:D coffee? ...I'm with you Gary the room is getting stuffy we need a break ;)

[nevgee]

Or we need to adjust the Apparatus Dew Point ... or maybe change the BPF by allowing some dirt into the heat exchanger ... or letting someone open a few doors ... or windows ... I don't know ... perhaps some human factor to just mess it all up anyway. :)

As I said the world isn't perfectly round. But the book may say different. Who knows :confused:

Coffee? double shot please!

[DTLarca]

From a design/component sizing point of view, the SHR is important, but irrelevant to comissioning/servicing.

To my mind SHR is beside the point, RH is the point.


It's like an engineer I recently spoke to regarding a walk-in he looked at for us. I asked him what the subcool and superheat was. He said he did all that superheat and subcool stuff at college 20 years back but he no longer remembers what that all is. He said he has had success repairing systems now for 20 years so none of that can be very important.

I told him he would be surprised how much it helps his daily life if he took the time to get familiar with it all. I told him I do not doubt he has been able to get the systems working all these years - that was not in question otherwise we would not have subbed work to him.

You guys don't care much for BPF and ADP or SHR etc - well cool - i don't doubt you get by without caring much about it. But I know you are wrong when you imply that because of that it is therefore a load of trivia.

But if you don't know much about it then how can you be so sure you were always getting stuff right. Just because the customers have been happy all this time it doesn't necessarily mean you got it right every time.

On a 1000kW system it can mean £40,000.00 savings in electricity every year - at least.

[DTLarca]

Or we need to adjust the Apparatus Dew Point ... or maybe change the BPF by allowing some dirt into the heat exchanger ... or letting someone open a few doors ... or windows ... I don't know ... perhaps some human factor to just mess it all up anyway. :)

As I said the world isn't perfectly round. But the book may say different. Who knows :confused:

Coffee? double shot please!

Oops - the chilled ceilings are dripping water - quick - what are we going to do about the high effective SHR? :D

[nevgee]

nevgee, human comfort is first of all mostly effected by radiant temperatures and in particular radiant temperature asymmetries, secondly by dry bulb temperatures, thirdly by drafts, fourthly by discrepancies between neck and ankles greater than 3K and down the list we eventually come to humidity..

You failed to point out that everyone has a differing level of perceived comfort. Women greater than men. Then of course the children and the aged and infirm, those who may be at rest or active ... .so many variables and you didn't mention them ... I think you're getting tired, Ah, another physiological reason for temperature perception.

Is it so important? Nadda ... no ... niche ... La ... nien

[nevgee]

Ah Subcooling and superheat .... I can agree with you there .... I find it very suprising how many guys don't appreciate the value of those values

[DTLarca]

You failed to point out that everyone has a differing level of perceived comfort. Women greater than men. Then of course the children and the aged and infirm, those who may be at rest or active ... .so many variables and you didn't mention them ... I think you're getting tired, Ah, another physiological reason for temperature perseption.

Is it so important? Nadda ... no ... niche ... La ... nien

Yup - we can take that approach with subcool and superheat too :)

Beer can cold - badda badda bish bang bing bong - job done - customers happy - Is subcool and superheat so important? Nadda nix - load of tosh all that design crap!!

[nevgee]

But if you don't know much about it then how can you be so sure you were always getting stuff right.




You presume too much I think :(

[DTLarca]

You presume too much I think :(

Presume too mcuh - what - about the subby who told me he doesn't need to know about subcool and superheat - that it is not important?

I told him also that there were a lot more problems out there possibly still waiting remedy that were staring him in the face but because he did not understand subcool and superheat he simply had no idea they existed. He shook his head in disbelief. I didn't tell him that a few weeks prior our top engineer who knows his subcool and superheat pretty well followed him up on a site to repair the leak he reported. Turned out the condensing unit was dirty and the evaporator was dirty (cold room) and after both were cleaned the room temp came down and the sight glass cleared. He may think I presumed too much but then that is how irony works - doesn't it :)

[mad fridgie]

It's like an engineer I recently spoke to regarding a walk-in he looked at for us. I asked him what the subcool and superheat was. He said he did all that superheat and subcool stuff at college 20 years back but he no longer remembers what that all is. He said he has had success repairing systems now for 20 years so none of that can be very important.

I told him he would be surprised how much it helps his daily life if he took the time to get familiar with it all. I told him I do not doubt he has been able to get the systems working all these years - that was not in question otherwise we would not have subbed work to him.

You guys don't care much for BPF and ADP or SHR etc - well cool - i don't doubt you get by without caring much about it. But I know you are wrong when you imply that because of that it is therefore a load of trivia.

But if you don't know much about it then how can you be so sure you were always getting stuff right. Just because the customers have been happy all this time it doesn't necessarily mean you got it right every time.

On a 1000kW system it can mean £40,000.00 savings in electricity every year - at least.
I think you are mis understanding SHR, is simply a calculation of the process Energy in, Energy out split between sensible and latent. When designing you calc on a steady state, or I should say Ideal, then design should allow for variations from steady state.
Many but not all, may use different methods to calculate load profiles, relying on various test equipment, flow, preesure temp humidity. You can only have a set of ideal SHR conditions under a set of fixed process conditions, the process conditions change then so must the ideal SHR conditions change. So what i am saying is actual SHR is irrelevent, unless the you have the ideal process SHR for that particular plant aand the different conditions, of which the average engineer on site is not going to have at hand.

[DTLarca]

I think you are mis understanding SHR, is simply a calculation of the process Energy in, Energy out split between sensible and latent. When designing you calc on a steady state, or I should say Ideal, then design should allow for variations from steady state.

What makes you think I misunderstand it?

[mad fridgie]

What makes you think I misunderstand it?
I applogise for how that read, (not my intention), my fingers were typing slower than the brain was thinking. I think you misunderstand how SHR is applied out in the field, and how many of us are aware of it as a load profile and how irrelevent the SHR% is, unless you know the particular process variables. You may SHR as your control variable within your software, but surely must have a floating set point to meet the process variables, there are many methods of control, how to reach optimum performance ( meeting process requirments and energy efficiency) is very plant specific

[DTLarca]

I applogise for how that read, (not my intention), my fingers were typing slower than the brain was thinking. I think you misunderstand how SHR is applied out in the field, and how many of us are aware of it as a load profile and how irrelevent the SHR% is, unless you know the particular process variables. You may SHR as your control variable within your software, but surely must have a floating set point to meet the process variables, there are many methods of control, how to reach optimum performance ( meeting process requirments and energy efficiency) is very plant specific

In the world of philosophical logic we say that a theory that explains everything explains nothing.

Global generalisation like "Plant Specific" sound precise but in fact are so vague they are meaningless. Propositions are either analytic or synthetic and synthetic statements while being contingent or a posteriori are meaningless if they in principle at least cannot be varified and no option is left open for them to be falsified.

The problem with such statements is that they are so easily converted from synethetic to analytic. The no true Scotsman Fallacy is a good example:
http://en.wikipedia.org/wiki/No_true_Scotsman

Anyway - say it was you instead of me who was called to the Natural History Museum to try solve the problem of Darwin's specimen bottle label's ink running.

Simply by manipulating the operation of the plant how do you first estimate the space SHR and then the plants effective SHR? What common factors would you look at to see where things might have gone wrong.

[mad fridgie]

Firstly lest clarify SHR
Semsible Heat Ratio = the amount of energy remove by an evaporator split into the two types of energy remove sensible and latent. (drop in temp and moisture removed)

[mad fridgie]

In the world of philosophical logic we say that a theory that explains everything explains nothing.

Global generalisation like "Plant Specific" sound precise but in fact are so vague they are meaningless. Propositions are either analytic or synthetic and synthetic statements while being contingent or a posteriori are meaningless if they in principle at least cannot be varified and no option is left open for them to be falsified.

The problem with such statements is that they are so easily converted from synethetic to analytic. The no true Scotsman Fallacy is a good example:
http://en.wikipedia.org/wiki/No_true_Scotsman

Anyway - say it was you instead of me who was called to the Natural History Museum to try solve the problem of Darwin's specimen bottle label's ink running.

Simply by manipulating the operation of the plant how do you first estimate the space SHR and then the plants effective SHR? What common factors would you look at to see where things might have gone wrong.
Prior to making changes you must understand the processes.
I would presume that they have a desire dry bulb temp? (lets say yes, just for ease) Then we need to know at this temperature, at what humidity does the ink run (normally contact ink manufacture), So know we have point, we then can calculate the resperation rate of the plants. external load requirements, then we need to know the fresh air make up and under what conditions this enters. We then can calculate max and min enthalpy of the evap entering air, we know the required air outlet quality. From this we can design the coil or if already existing the required SST to achieve the desired results. the design is easy it is all about the process. Depending upon what is variable within the system, would determine how you would control for optimum efficiency. (and dare I say how much the client is willing to pay, which in many cases is the actual limiting factor)

[DTLarca]

Firstly lest clarify SHR
Specific Heat Ratio = the amount of energy remove by an evaporator split into the two types of energy remove sensible and latent. (drop in temp and moisture removed)

SHR = SH/(SH+LH)

Where SH+LH = Total heat or TH

SHR = SH/TH

The room SHR and the effective AHU SHR need to be similar but when fresh air is involved the coil SHR will usually be lower than the other two.

[DTLarca]

From this we can design the coil or if already existing the required SST to achieve the desired results.

Correct :)

Do how do we adjust the SST.

BTW - I did not ask how to calculate the room SHR - I asked how you would imply it as in by introducing an instability to the room to monitor the ensuing rates of change.

[mad fridgie]

Correct :)

Do how do we adjust the SST.

BTW - I did not ask how to calculate the room SHR - I asked how you would imply it as in by introducing an instability to the room to monitor the ensuing rates of change.
If I do not know the reqired enthalpy, then how do I know what to adjust the SST to. thus you do need to calculate!
How to do it so many ways and is plant specific, if you have excess refrigeration capacity and capacity control of the compressors, it may just be as simple as adjusting suction set point! This bit really comes down to what you have. I do not have problems only solutions waiting to be found.!

[mad fridgie]

Appologies to the OP, we seem to have highjacked your thread!
Give use some pics mate! Then we can get back on track!

[DTLarca]

If I do not know the reqired enthalpy, then how do I know what to adjust the SST to. thus you do need to calculate!
How to do it so many ways and is plant specific, if you have excess refrigeration capacity and capacity control of the compressors, it may just be as simple as adjusting suction set point! This bit really comes down to what you have. I do not have problems only solutions waiting to be found.!

You are not designing the system so you do not need specifics - ratios will do.

So for DX yes you lower the SST but by merely lowering the Suction Pressure Set Point you have also increased sensible cooling and thus you have just given the RH a cause to rise precisely when you wanted it to drop. So what would be a better solution?

Also - what would you do if it was a chilled water cooled AHU?

[mad fridgie]

You are not designing the system so you do not need specifics - ratios will do.

So for DX yes you lower the SST but by merely lowering the Suction Pressure Set Point you have also increased sensible cooling and thus you have just given the RH a cause to rise precisely when you wanted it to drop. So what would be a better solution?

Also - what would you do if it was a chilled water cooled AHU?
True scotsman, how long is a piece of string. Does the system have re-heat, by-pass dampers, variable airflow, variable refrigeration capacity and so on. The system will determine the fix, are there any money limitations.
Chilled water, is it a dedicated chiller or common, plus all of the above.
You gather information before you make your changes, or you pay for the best to do it for you. and I do cost!

[Gary]

I'm still waiting to hear how SHR is relevant to service.

[Gary]

Appologies to the OP, we seem to have highjacked your thread!
Give use some pics mate! Then we can get back on track!

We are just entertaining each other while we wait for the OP's return. :)

[mikeref]

We are just entertaining each other while we wait for the OP's return. :)
Damn, you boys still gassbagging? This latest debate has taken most of my saturday with intense interest, and i went out with the MRS. Mikeref for some ( boring) shopping during it all. I am waiting with anticipation for our host to return with pics or info on his dilemma..;).. mike.

[nevgee]

I'm still waiting to hear how SHR is relevant to service.


... and especially a kitchen fresh air system !

The potato croquettes might go soggy or perhaps the ink on the waiter's tickets might run :D

Bearing in mind we're not talking plant specifics here as that would be too generalised. :confused:

[NoNickName]

I'm still waiting to hear how SHR is relevant to service.

Very relevant, and the fact that overcharging or undercharging effects subcooling, it also effects the performance of the evaporator, which in turn effects the evaporating temperature, and in turn increases or reduces the latent heat removal.
But as DTLarca says:


It's like an engineer I recently spoke to regarding a walk-in he looked at for us. I asked him what the subcool and superheat was. He said he did all that superheat and subcool stuff at college 20 years back but he no longer remembers what that all is. He said he has had success repairing systems now for 20 years so none of that can be very important.

Very few refrigeration engineers know their stuff. It's like working in a tyre service center and not knowing what camber or caster is just because he only happens to repair punctures.
DTLarca made a very good point there.



Sensible Heat Ratio is preset at design given specific design parameters.

But when working conditions change, SHR changes.
Failing to recognise that, makes a epic failure of your job.
SHR is not a constant figure along the operational envelope.



There are many peeps who sit at their drwng brds believing that the world is perfectly round

In need of some examples of refrigeration engineers or installers failures?

[mad fridgie]

NNN, On site SHR, is a result of the plant and conditions, Yes the specifics of the plant, SCT, SST, sub cooling superheat all effect the result, but a pre determined SHR% is not for the service guys, it is the required end result that he is aiming for.
For this reason SHR is not a service tool or term, even if indirectly it is what they are actually measuring.

[DTLarca]

... and especially a kitchen fresh air system !

The potato croquettes might go soggy or perhaps the ink on the waiter's tickets might run :D

Bearing in mind we're not talking plant specifics here as that would be too generalised. :confused:

And when a butcher complains that his meat is too "soggy" - he can't slice through it - when he tries to cut it the meat just rolls with his knife. Simple solution - isolate one of the fans, blank that fans discharge - SHR reduces and meat is now cuttable with negligable loss in weight :)

[DTLarca]

True scotsman, how long is a piece of string. Does the system have re-heat, by-pass dampers, variable airflow, variable refrigeration capacity and so on. The system will determine the fix, are there any money limitations.
Chilled water, is it a dedicated chiller or common, plus all of the above.
You gather information before you make your changes, or you pay for the best to do it for you. and I do cost!

The length of a piece of string - it depends on how how many angels you can stand on a pin head.

Now you are being wonderfully specific about those "previously mysterious plant specifics you were waffling on about" :)

Remember - we are not so much talking about service engineers here as we are about commissioning engineer. Though I for one expect my service engineers to also be commissioning engineers.

Regarding SHR control...

Reheat - so often made to work but horribly inefficiently on account of poor understanding of SHR and energy consumptions.

Face and Bypass - not very effective with chilled water systems.

variable air flow - not very effective with chilled water systems.

Variable refrigeration system capacity - ideal when both SH capacities are insufficient and SHR's are too high - not of any help if only the SHR is too high.

So it seems you do know a little more about SHR than the average person in the industry - perhaps too much to realise how important it is knowing it - you have forgotten what it means to not understand it but to be aware of it :)

[DTLarca]

Sample Level 3 Exam Question...

One of the most important factors governing humidity in a refrigerated space is?...

The evaporator to air temperature difference?
Compressor superheat?
Condenser to air temperature difference?
Suction superheat?

[DTLarca]

Another example Level 3 Exam Question - image attached.

[mad fridgie]

The length of a piece of string - it depends on how how many angels you can stand on a pin head.

Now you are being wonderfully specific about those "previously mysterious plant specifics you were waffling on about" :)

Remember - we are not so much talking about service engineers here as we are about commissioning engineer. Though I for one expect my service engineers to also be commissioning engineers.

Regarding SHR control...

Reheat - so often made to work but horribly inefficiently on account of poor understanding of SHR and energy consumptions.

Face and Bypass - not very effective with chilled water systems.

variable air flow - not very effective with chilled water systems.

Variable refrigeration system capacity - ideal when both SH capacities are insufficient and SHR's are too high - not of any help if only the SHR is too high.

So it seems you do know a little more about SHR than the average person in the industry - perhaps too much to realise how important it is knowing it - you have forgotten what it means to not understand it but to be aware of it :)
Correct I know nothing about refrigeration, just I just make it up i as I go along! Luckly for me people had paid I fortune for my lack knowledge and for a number patented systems that are now used around the world, i just a con man! Especially around the world on industrial drying, somehow by luck again I reduced input energy cost down by in the best case by 81%, i just do not know how i achieved these results without using the Term SHC, i do remember, i think we a thing called enthalpy of an, in and out stream of air, I also think that vapour pressure was brought into the calculation, no i am wrong i wet my finger flung it around, got my design.
You asked a question about a plant i asked what was in the plant, giving some examples. How can I resolve a problem if i am not aware of the practical limitations of the plant, as well as know nothing I am neither a mind reader.

[mad fridgie]

Lets see what you really know. Why does you ink run!, because it is wet does not count, why is it wet!

[DTLarca]

Correct I know nothing about refrigeration, just I just make it up i as I go along! Luckly for me people had paid I fortune for my lack knowledge and for a number patented systems that are now used around the world, i just a con man! Especially around the world on industrial drying, somehow by luck again I reduced input energy cost down by in the best case by 81%, i just do not know how i achieved these results without using the Term SHC, i do remember, i think we a thing called enthalpy of an, in and out stream of air, I also think that vapour pressure was brought into the calculation, no i am wrong i wet my finger flung it around, got my design.
You asked a question about a plant i asked what was in the plant, giving some examples. How can I resolve a problem if i am not aware of the practical limitations of the plant, as well as know nothing I am neither a mind reader.

I don't doubt you manage with your work and I don't doubt that your patents are valid and sound.

Many people have enormous success at varying things but strangely all along never know as much as we expected them to know about their field of expertise.

You must remember that I did ask you two pretty specific questions and in both cases your replies amounted to "Well it depends" and "How long is a piece of string" when in fact there is only one fundamental way to reduce the SHR on a cooling coil. There are many ways to adjust the SHR of an overall system by adding additional apparatus to it but there is only one fundamental way to reduce the SHR on a cooling coil and if you have a mastery of SHR control you would immediately start with this one fundamental in your explanations. You did do this but half heartedly when you suggested reducing SST.

And there are ways to determine a rooms SHR by simply introducing a transitional instability and monitoring the reaction - you do not have to do all the calculations if the system already exists - but you do if the system is in design.

[DTLarca]

Lets see what you really know. Why does you ink run!, because it is wet does not count, why is it wet!

As Newton said "I do not know why the planets go the way they do - I can only use math to describe the way they go".

Why is there capillary action? Why are there weak intermolecular forces i.e. why is there capillary action with water and not with murcury? I don't know - I don't know why - I can only explain the way it happens.

[mad fridgie]

I don't doubt you manage with your work and I don't doubt that your patents are valid and sound.

Many people have enormous success at varying things but strangely all along never know as much as we expected them to know about their field of expertise.

You must remember that I did ask you two pretty specific questions and in both cases your replies amounted to "Well it depends" and "How long is a piece of string" when in fact there is only one fundamental way to reduce the SHR on a cooling coil. There are many ways to adjust the SHR of an overall system by adding additional apparatus to it but there is only one fundamental way to reduce the SHR on a cooling coil and if you have a mastery of SHR control you would immediately start with this one fundamental in your explanations. You did do this but half heartedly when you suggested reducing SST.

And there are ways to determine a rooms SHR by simply introducing a transitional instability and monitoring the reaction - you do not have to do all the calculations if the system already exists - but you do if the system is in design.
OK you drop your SST and starve the coil "increasing the super heat." But do you understand what happens to the rest of the system with excessive superheat

[DTLarca]

OK you drop your SST and starve the coil "increasing the super heat." But do you understand what happens to the rest of the system with excessive superheat

I have thought for many hours about that one before, that is not how I would drop SST, but that would work.

Could you give me an example of when lowering the SHR does not reduce overall system EER?

Even fitting heat pipes before and after the evap coil adds air resistance and lowers circuit COP.

[DTLarca]

As Newton said "I do not know why the planets go the way they do - I can only use math to describe the way they go".

Why is there capillary action? Why are there weak intermolecular forces i.e. why is there capillary action with water and not with murcury? I don't know - I don't know why - I can only explain the way it happens.

Others have spent time explaining the way these things go - but still no one knows why...
http://en.wikipedia.org/wiki/Capillary_action

[mad fridgie]

I have thought for many hours about that one before, that is not how I would drop SST, but that would work.

Could you give me an example of when lowering the SHR does not reduce overall system EER?

Even fitting heat pipes before and after the evap coil adds air resistance and lowers circuit COP.
Drop your SCT

[mad fridgie]

Lets see what you really know. Why does you ink run!, because it is wet does not count, why is it wet!
Answer "vapour pressure"

[DTLarca]

Drop your SCT

That is often the first place to start if it is a service matter. If your SCT is at design and your condenser capacity is at max, say max fans at max speed, then you cannot drop it any significant amount without some radical addition or modification to the plant - say atomized spray water.

If you were going to modify the plant to drop SST but maintain or even reduce SH then adding a mechanical subcooling circuit would do a great job and you'd regain efficiency overall - the two bits of plant combined will have a higher EER.

[DTLarca]

Answer "vapour pressure"

Interesting comment - you've got me all excited now. Tell me more?

I would have thought the increased vapour pressure (raised dew point) would result in weak molecular attraction level of forces causing the water to condense into the paper and ink in the paper. As the wiki link say - water's intermolecular forces are weaker than the forces between the molecules and the paper and so when the ink is taken back into solution with water the waters attraction to the paper causes it to run with the ink.

But I'm not saying much - I'm now out of my league - I'm more comfortable sticking to HVACR.

[DTLarca]

Interesting comment - you've got me all excited now. Tell me more?

I would have thought the increased vapour pressure (raised dew point) would result in weak molecular attraction level of forces causing the water to condense into the paper and ink in the paper. As the wiki link say - water's intermolecular forces are weaker than the forces between the molecules and the paper and so when the ink is taken back into solution with water the waters attraction to the paper causes it to run with the ink.

But I'm not saying much - I'm now out of my league - I'm more comfortable sticking to HVACR.

Also - as the water vapour is absorbed by the paper and ink would there not also be heat of absorption helping to loosen the ink from the paper fibers it has for so many years temporarily settled on?

[mad fridgie]

That is often the first place to start if it is a service matter. If your SCT is at design and your condenser capacity is at max, say max fans at max speed, then you cannot drop it any significant amount without some radical addition or modification to the plant - say atomized spray water.

If you were going to modify the plant to drop SST but maintain or even reduce SH then adding a mechanical subcooling circuit would do a great job and you'd regain efficiency overall - the two bits of plant combined will have a higher EER.
Have a guess of what I manufacture! have a guess what a number of my patents relate to.

[DTLarca]

Drop your SCT

I have attached a couple of photo's from a data center cooling system I consulted on doing all the load calcs, equipment selection, controls philosophies and pipework (distribution) design and so forth. In other words a real life example of what we are talking about - the importance of understand SHR.

So some questions to entertain your intellect :)
What do you think is my designed SHR and how would energy be wasted if it is not commissioned to design intentions but rather is naively commissioned only to design spec?

[DTLarca]

Have a guess of what I manufacture! have a guess what a number of my patents relate to.

Nope - can't do it - but I am very curious :)

[mad fridgie]

air, moisture, products (including SHR)
Think of air as a sponge, it is dry and sitting on the bench, 0% RH, dunk totally in water, 100% RH.
Squeeze the sponge a bit (which means either increased air pressure or cooling down, basically both are contracting the mass), what comes out , "water" what is the present RH 100%, now release it in the air, what is the RH (between 0 and 100%, depends upon how much you squeezed) no place on the bench, leave for a minute, lift up what will you see, water because the water had more pressure excerted than the bench pushed up (in this case gravity)

[mad fridgie]

Nope - can't do it - but I am very curious :)
Liquid sub coolers!

[DTLarca]

Liquid sub coolers!

Lol - I should have said so - that did cross my mind because you asked the question right on top of my subcooling comment.

Cool :)

[DTLarca]

air, moisture, products (including SHR)
Think of air as a sponge, it is dry and sitting on the bench, 0% RH, dunk totally in water, 100% RH.
Squeeze the sponge a bit (which means either increased air pressure or cooling down, basically both are contracting the mass), what comes out , "water" what is the present RH 100%, now release it in the air, what is the RH (between 0 and 100%, depends upon how much you squeezed) no place on the bench, leave for a minute, lift up what will you see, water because the water had more pressure excerted than the bench pushed up (in this case gravity)

I love thermodynamics so I have developed what I believe to be a lecture with methods of explanations better than none other to impart to others an uderstanding of psychrometrics.

Dalton law of partial pressures is required first. But only after I have rid people minds of the catasrophy of the spunge analogy which actually detracts from peoples ability to develop an understanding of psychrometrics. I have attached an example slide randonly selected from about 10 slides I use to convery this first principle that is mean to dispense with the spunge analogy.

[DTLarca]

Sorry - hit the submit button rather than the manage attachments button...

Here is the slide...

[nevgee]

I love thermodynamics so I have developed what I believe to be a lecture with methods of explanations better than none other to impart to others an uderstanding of psychrometrics.




Problem is matey ...... your over enthusiastic, overwhelming "love" for thermodynamics has tended to cause a lot of peeps to yawn and ask the question ....Why are we listening to this?

It's not required at the moment... You seem to have gotten lost in your own world of over egged responses to an in field problem with a total loss vent system that isn't working.

Go back to the begining of this thread and read what the poor OP was asking in the first place.

He needed some help, not a rant on the mysteries of thermodynamics.

I feel sorry for you in some respects because I can understand how you want to give up the knowledge you hold so dearly, to those who aren't so fortunate to have the ability that you quite clealy have. I can see you're something of a very talented chap. You can quote garrulously with technical and philosphically sounding arguements. You hold a magical esteem of yourself which comes over something a tad pompous, and I suspect because of this challenging nature that you exude there have been a few people willing to run with you for a while. However, I wouldn't be suprised if the original poster has gone off wondering why he ever bothered .... because he didn't get any help from reading your pontifications about the benefits of SHR's

It would, in all fairness to willsmithiraq, been better to have moved your lectures over to another thread where you could discuss the flavour of the cheese in the moon to your heart's content. :D

[DTLarca]

Problem is matey ...... your over enthusiastic, overwhelming "love" for thermodynamics has tended to cause a lot of peeps to yawn and ask the question ....Why are we listening to this?

It's not required at the moment... You seem to have gotten lost in your own world of over egged responses to an in field problem with a total loss vent system that isn't working.

Go back to the begining of this thread and read what the poor OP was asking in the first place.

He needed some help, not a rant on the mysteries of thermodynamics.

I feel sorry for you in some respects because I can understand how you want to give up the knowledge you hold so dearly, to those who aren't so fortunate to have the ability that you quite clealy have. I can see you're something of a very talented chap. You can quote garrulously with technical and philosphically sounding arguements. You hold a magical esteem of yourself which comes over something a tad pompous, and I suspect because of this challenging nature that you exude there have been a few people willing to run with you for a while. However, I wouldn't be suprised if the original poster has gone off wondering why he ever bothered .... because he didn't get any help from reading your pontifications about the benefits of SHR's

It would, in all fairness to willsmithiraq, been better to have moved your lectures over to another thread where you could discuss the flavour of the cheese in the moon to your heart's content. :D

I am standing in defence of the proposition that knowledge of SHR is useful. You may very right about everything you say about me - you may be wrong - I am not interested in which, if any, it is - and whatever it happens to be it would still be irrelevant to the question "Is there any need for a commissioning engineer to have a good understanding of SHR control?".

You have gone silent on that quest? Are you avoiding it?

[DTLarca]

Problem is matey ...... your over enthusiastic, overwhelming "love" for thermodynamics has tended to cause a lot of peeps to yawn and ask the question ....Why are we listening to this?

It's not required at the moment... You seem to have gotten lost in your own world of over egged responses to an in field problem with a total loss vent system that isn't working.

Go back to the begining of this thread and read what the poor OP was asking in the first place.

He needed some help, not a rant on the mysteries of thermodynamics.

I feel sorry for you in some respects because I can understand how you want to give up the knowledge you hold so dearly, to those who aren't so fortunate to have the ability that you quite clealy have. I can see you're something of a very talented chap. You can quote garrulously with technical and philosphically sounding arguements. You hold a magical esteem of yourself which comes over something a tad pompous, and I suspect because of this challenging nature that you exude there have been a few people willing to run with you for a while. However, I wouldn't be suprised if the original poster has gone off wondering why he ever bothered .... because he didn't get any help from reading your pontifications about the benefits of SHR's

It would, in all fairness to willsmithiraq, been better to have moved your lectures over to another thread where you could discuss the flavour of the cheese in the moon to your heart's content. :D

The ad hominem fallacy is committed when an antagonist brings into the discussion an irrelevancy.

If someone argued that we should not take seriously the findings of a medical scientist who had researched the beneficial effects of jogging on the cardiovascular system on the grounds that the scientist was overweight and probably could not even run 100 yards then a matter utterly irrelevant to the topic at hand would have been introduced to the discussion. The antagonist might just as well have stated that in Spain it rains mainly on the plains for all it adds to the topic at hand. Because the two claims can be true at the same time. They are not mutually exclusive. The one does not contradict the other and nor is the one contrary to the other. In which case the antagonist has merely changed the subject to an irrelevance.

As I say, you might even be right about your claims of me but this is not actually the time nor place to discuss such matters so I'd rather we get back onto the the other very unrelated topic of the benefits of understanding SHR manipulation.

You see, I am not asking people to take my claims on faith or on testament but instead by analysis of the evidence and argument I present. And anyway even if you were right about me none of that necessarily detracts on its own from any value my testament might have if it was mere testament rather than argument and evidence I was offering.

If someone is introducing an irrelevancy then it is good enough simply to remind them that they have changed the subject and that you would like to finish the discussing the topic at hand before moving on the other topics.

I cannot see how the original poster would be dished a disservice by all of the ensued technical speculations. You are introducing greater irrelevancies than I might have done in the first place - fighting fire with fire doesn't always word - sometimes it merely amounts to two wrongs.

[DTLarca]

In need of some examples of refrigeration engineers or installers failures?

Cynics, skeptics, pessimists and relativists.

Cynics suggest nothing matters, skeptics keep and open mind, pessimists throw their arms in the air and claim it's all pointless and relativists are willing to swing in any direction.

Skepticism is healthy if it is inquiring skepticism - if it is participatory skepticism. Over the ages the many intellectually liberating antimonies - particularly those of Sextus Empiricus, Descartes, Hulm and Kant.

I am a strong skeptic - I challenge - break apart - then rebuild - every synthesis of information that comes my way.

It's only the cynical pessimists that are averse to technical speculations. There was a time - it seems nearly a decade back now - when I once started a forum category called "Technical Speculations" and speculating there but anywhere else too was quite an accepted past time. unfortunately there are too few constructive skeptics in our industry.

[Gary]

And I still don't see the relevance of SHR to service.

If I know the required temp and RH, I can make it happen without evaluating or knowing anything about the SHR.

It's all about the condition of the supply air.

[NoNickName]

Way off topic. I give up. Unsubscribing the thread.

[DTLarca]

And I still don't see the relevance of SHR to service.

If I know the required temp and RH, I can make it happen without evaluating or knowing anything about the SHR.

It's all about the condition of the supply air.

I'm about to go north 3 hrs drive for a few days so I shall leave you in peace.

I will probably be barred from accessing these forums again shortly anyway :)

I'm also not sure what relevence SHR has to service except to say that in the same way a tech knows more about a system if he/she understands the dynamics of Subcool he/she knows more about the system if he/she understands the dynamics of SHR (i.e. ADP)

But I will say that if you tried to answer my question put further up this thread on the data centre SHR commissioning to design intention versus commissioning to spec then you might gain an appreciation of SHR with regards to being a good commissioning engineer.

Then come back and explain what you mean by "It's all about the condition of the supply air" and how this somehow excludes any SHR implications.

Then read Malcolm Gladwell's Book called Blink and the power of thin slice thinking and how it is increased with learning but the learning must not cloud the actual on site real situation analysis - but that on site situational analysis is vastly improved with leasure-time studying of the topic material to as great a depths as possible.

Also, as Socrates say in the Theatatus "How do you know you have found what you are looking for if you do not know what you are looking for?" Which direction do you head in search of it if you don't even know what it is - how do you know it is not your problem if you don't even know what it is?

With 20% of the required knowledge we can fix 80% of the problems. All added knowlege comes with diminishing returns. And if everyone knows only the same 20% then anyone who knows more seems out of kilter and since everyone get's along facing the same 80% of problems leaving the systems 80% good who's going to care about the 20% missing performance or longivity especially if no body is even aware of its possibilities.

Later Gary - also - check your mail :)

[nevgee]

I am standing in defence of the proposition that knowledge of SHR is useful.

I don't disagree with you on this.

.......it would still be irrelevant to the question "Is there any need for a commissioning engineer to have a good understanding of SHR control?".

You have gone silent on that quest? Are you avoiding it?

No not avoiding it at all, but it was your question that you were ranting on about not the one from the OP. We should be staying on topic and helping the guy to solve a problem, not adding confusion to the issue.

I can just imagine Winston Churchill trying to get the bouncing bomb into a mission and some boffin (aka yourself) arguing that there were some fundimental issues covering the triple point of water in Norway on a winter's night, that needed to be adressed and may have some bearing on the way the bomb may or may not bounce.

;)

[nevgee]

I'm about to go north 3 hrs drive for a few days so I shall leave you in peace.

I will probably be barred from accessing these forums again shortly anyway :)

I'm also not sure what relevence SHR has to service except to say that in the same way a tech knows more about a system if he/she understands the dynamics of Subcool he/she knows more about the system if he/she understands the dynamics of SHR (i.e. ADP)

But I will say that if you tried to answer my question put further up this thread on the data centre SHR commissioning to design intention versus commissioning to spec then you might gain an appreciation of SHR with regards to being a good commissioning engineer.

Then come back and explain what you mean by "It's all about the condition of the supply air" and how this somehow excludes any SHR implications.

Then read Malcolm Gladwell's Book called Blink and the power of thin slice thinking and how it is increased with learning but the learning must not cloud the actual on site real situation analysis - but that on site situational analysis is vastly improved with leasure-time studying of the topic material to as great a depths as possible.

Also, as Socrates say in the Theatatus "How do you know you have found what you are looking for if you do not know what you are looking for?" Which direction do you head in search of it if you don't even know what it is - how do you know it is not your problem if you don't even know what it is?

With 20% of the required knowledge we can fix 80% of the problems. All added knowlege comes with diminishing returns. And if everyone knows only the same 20% then anyone who knows more seems out of kilter and since everyone get's along facing the same 80% of problems leaving the systems 80% good who's going to care about the 20% missing performance or longivity especially if no body is even aware of its possibilities.

Later Gary - also - check your mail :)
:off topic: :off topic: :off topic: :off topic: :off topic: :off topic:

Antogonistic? You sabbotaged the whole thread :mad:

[nevgee]

I Give up :confused:

[Gary]

I'm still waiting for the OP to return with further info, so we can get back to his problem.

[nevgee]

Gary,

I fear he's long gone. . . He's enough on his plate without trying to read through all of the above ... not helpful really. I'm as guilty as anyone for contributing.
Happy Sunday ... tomorrow's Monday . yippee

[Gary]

I doubt seriously that we chased him away with our riveting discussion of SHR.

More likely he is busy with other things and hasn't gotten back to the system in question yet... or he figured it out and moved on.

[DTLarca]

Antogonistic? You sabbotaged the whole thread :mad:

I did not say antagonistic - I said antagonist

Antagonist: a person who is opposed to, struggles against, or competes with another; opponent; adversary.

Antagonistic: hostile; unfriendly.

If you think I meant antagonistic then maybe that has more to do with your own perception of yourself.


Sensible Heat Ratio is preset at design given specific design parameters. Aparatus Dew Point and ByPass Factors are also predefined at design. I can't see how a commissioning Engineer is able to make any corrections to these factors when he is most like never to achieve designg conditions at all.

If you were to try square the implicitly invoked generalisations of the above argument universally then you would be being inconsistent if you did not equally assert that system total air volume flow and zone air volume flows are preset at design so you cannot see how a commissioning engineer is able to make any corrections to these factors.

No system meets perfectly the design parameters - in the UK CIBSE give percentage tolerances that ought to be met and that ought to be stated in the specifications.

With regard to SHR's - comfort cooling systems are more forgiving of deviations from design.

With data center close control systems enormous amounts of electrical energy is wasted when the CRAC SHR's are lower than the Rack Hall's SHR on account of excessively cold chilled water temperatures causing continuous unnecessary operation of the humidifier bottles. On the Global Switch project I was involved with - the biggest data centre in Europe - such ignorance during commissioning would amount to tens of thousands of £'s wasted monthly.

You should be able to count 26 1.5MW Air Cooled Chillers on the roof here...

http://maps.google.co.uk/maps?hl=en&q=canary+wharf&ie=UTF8&hq=Canary+Wharf&hnear=Canary+Wharf,+Poplar,+Greater+London+E14+4,+United+Kingdom&ll=51.51083,-0.003483&spn=0.000463,0.001629&t=h&z=20

In an asymmetric persuasion dialogue the person making the claim bares the burden of proof. This is when a protagonist makes a claim and the antagonist simply denies the acceptability of the argument and evidence offered. An example here is Me versus Gary. Gary has not made a counter claim - he has merely expressed skepticism and so bares no burden of proof.

In the persuasion dialogue between you and I we have both made claims - me for and you against - this is thus a symmetrical persuasion dialogue - you share equally a burden of proof for your claim as I do for mine. I am still waiting for your argument and evidence. You may yet turn out to be right but so far your argument is weak and your evidence is none.

[DTLarca]

I'm still waiting for the OP to return with further info, so we can get back to his problem.

Getting hold of the designers intentions would help. When is the system to operate in heating and when in cooling (What ambient temps) and what are the peak heating and cooling TD's and dT's.


Interesting... a built in bypass... clever :)

In the case of the 100% fresh air system for high but inactive occupancies you will over cool the occupants with normal supply air to return air dt's. Thus the high BPF but with maintained SHR.

On the other hand face and bypass over and around a coiling coil is for SHR variation.

[mad fridgie]

We are in the presence of a very well educated member (a compliment)
How ever you must be able to impart your knowledge in a way that those of us who are not as educated or skilled within your feild, that either is above our present knowledge levels, or a way that does not make us feel inferior.
Going Back, SHR, the "TERM" is used commonlly in Air conditioning, but is very rarely used in refrigeration (I know that they are basic the same side of the coin) Rightly or wrongly thats another question.
SHR is calculated figure, normally in refrigeration, the design engineer normally gives the tech, a set of criteria that the on site engineer should be aiming for, which if dealing with air could always be calculated SHR figure. what comes first the SHR or the onsite tech data.
So when passing my design data to engineers, I would give them a set of data that should occur under certain conditions.
"Air on" conditions, "Air off", refrigeration details, air pressure drops, and so on.
For this reason the guy on site does not need to use SHR as his main method of proving performance, even though if you used and calculated his collected data he would actually have a SHR figure.
Using SHR% as starting point is irrelevent unless you have pretermined reference points.
Moving off slightly I understand your point about your data centre and the humidity bottles, As I have mentioned, more use of enthalpy sensors should be used.

[DTLarca]

We are in the presence of a very well educated member (a compliment)

I'm willing to accept the compliment so long as you are able and willing, if necessary, to provide justification - perhaps backing it up with evidence - after also demonstrating you are qualified to issue such compliments - just kidding :)


How ever you must be able to impart your knowledge in a way that those of us who are not as educated or skilled within your feild, that either is above our present knowledge levels, or a way that does not make us feel inferior.

I don't know about the not as educated or skilled references - after all - to go through the motions of imparting knowledge one implicitly assumes, at this level of sharing, those listening are sufficiently educated but just per chance not in the know of this particular take of the spectrum.

I was also cruising along explaining stuff quite plainly up until the point a claim was made against me in a manner that implicitly suggested that person could underpin the claim with argument and evidence. I called the person's bluff and invited the argument and evidence. None came and at the same time I am not going to do their work for them by providing in full with every detail my own argument and evidence in defense. We have a right to assume that a person making a claim against a notion we propose will have valid and sound reasoning for doing so and will be also most willing to demonstrate that reasoning in an articulate manner - otherwise how can they themselves be sure of their own claims.

I have given a brief clue as to some of the SHR issues arising with Data Centre design and commissioning but there is a little more still to it. The photo's I posted of my recent consulting project is of a project where the matter of SHR is the very central foundational point upon which everything else, design wise, pivots.

If anyone wants to convince me that there is no point in a commissioning engineer understanding how to manipulate system SHR then they will have to first demonstrate to me they are qualified to draw such conclusions otherwise for all I know they could be sharing some old mistaken knowledge they were taught by some guy who was in turn taught by some other equally mistaken guy ad infinitum.

[mikeref]

DTLarca, could you explain how this sensible heat ratio has relevance to origional posters problem when he has not had the equipment running long enough to have a coffee break? He did not manufacture the parts, just there to put it together and make some customers request happen. It seems to me op may not have had the luxury of time to discuss above events, probably now working through component parts capacity with manufacturer or whoever supplied the equipment. thats what i would do... mike.

[DTLarca]

DTLarca, could you explain how this sensible heat ratio has relevance to origional posters problem.

It has no immediate relevance - there are more serious concerns this far.

The discussion on SHR springs from this inherently self defeating set of statements "Sensible Heat Ratio is preset at design given specific design parameters. Aparatus Dew Point and ByPass Factors are also predefined at design. I can't see how a commissioning Engineer is able to make any corrections to these factors when he is most like never to achieve designg conditions at all. I would find it very unusual that any one would have the luxury and satisfaction of designing an AHU system with ducting etc and for it to drop into a design performance for commissioning purposes. In a real world it never happens."

[Gary]

To manipulate the condition of the supply air (specifically wetbulb) as a means of controlling humidity levels is to manipulate the SHR, but needn't be thought of as a manipulation of the SHR, and needn't be couched in terms of SHR%.

It could simply be thought of as manipulating humidity, and the ends achieved without referring to SHR%.

To my mind, SHR% seems an unnecessary complication.

[mad fridgie]

I am no specialist on Data centres.
But lets have a go without looking for external Data.
I presume you are talking about a high energy density area (compact electronics) So all the load from these items is sensible energy, possibly at little latent load from people and the required amount of fresh infiltration/makeup.
We want to ensure that static electricity is not produced, therefore the humidity entering the process has to be high enough, that when the air picks up the load sensible energy that the humidity s still high enough to ensure static is not produced.
Now we have our return air/load.
how is it to be chilled, it is a dedicated chiller (water or DX), Ok is a perfect world, a floating set point on supply fluid/SST to meet the load profile whilst being high enough to ensure required high exiting humidity levels. On a multi use system, the working fluid/sst, must meet the lowest common requirement, so using a floating set point to control a modulating valve. if the area(s) are zoned, use of a air transducer and VSD to match the air requirment profile. Final introduce free cooling, based upon the enthalapy difference, allowing for cooling without the need for additional moisture (unless the moisture producing device is more econimical to run than the refrigerant plant.
All contolled by logic based upon wet/bulb conditions.

[mikeref]

Are you on the right page MAD?

[mad fridgie]

Are you on the right page MAD?
I am never on the right page lol. I blame it on the drink
No mention of SHR

[DTLarca]

Good effort there Mad Fridge.

Gary just does not want to admit that SHR is a better description of what he's talking about :)

[Gary]

Good effort there Mad Fridge.

Gary just does not want to admit that SHR is a better description of what he's talking about :)

Better is subjective. :)

"Everything should be made as simple as possible, but not simpler." - Albert Einstein -

[mikeref]

It has no immediate relevance - there are more serious concerns this far.


The discussion on SHR springs from this inherently self defeating set of statements "Sensible Heat Ratio is preset at design given specific design parameters. Aparatus Dew Point and ByPass Factors are also predefined at design. I can't see how a commissioning Engineer is able to make any corrections to these factors when he is most like never to achieve designg conditions at all. I would find it very unusual that any one would have the luxury and satisfaction of designing an AHU system with ducting etc and for it to drop into a design performance for commissioning purposes. In a real world it never happens."
Again, there are very few hard facts to go on here. How do you figure o.p's day started out? Hmm, have to do my SHR first, no, it just won't work because i haven't seen it, then i'll pipe it up anyway- DONT think so. If i were to put together a system, it would be selected on data supplied by manufacturers who have done the ground work for their products.If that is not acceptable then who do you place your trust in? I think, in OP's case, he was placed there after the fact, where others had made the choices beforehand.

[Willsmithiraq]

Right guys, I am still here!! And so is this thread! I just hope the internet system doesn't go down again as I'll have to read through another 4 pages of replies!!

As Gary said unfortunately I've been pulled to other jobs and haven't been able to get back to the job in question . The manufacturer is coming back to us today with a "solution" apparently so as soon as I know you guys will know.

The pics will also be included as and when I get back to the job.

Appreciate all the replies even though quite a lot of it was over my head!! Nice to know people are still interested in helping others!!

Cheers guys and will post soon!

[mikeref]

Right guys, I am still here!! And so is this thread! I just hope the internet system doesn't go down again as I'll have to read through another 4 pages of replies!!

As Gary said unfortunately I've been pulled to other jobs and haven't been able to get back to the job in question . The manufacturer is coming back to us today with a "solution" apparently so as soon as I know you guys will know.

The pics will also be included as and when I get back to the job.

Appreciate all the replies even though quite a lot of it was over my head!! Nice to know people are still interested in helping others!!

Cheers guys and will post soon!
Well, hello stranger, nice of you to come back into our domain. We have been wondering how you have been getting on. your ears must have been burning, LOL!:D.. Mike.

[Willsmithiraq]

And the winner is.....................Hot gas bypass!!! Here's the first piece of sketchy info I've had so far. See attached pdf. Further details to be sent from manufacturer.

[DTLarca]

And the winner is.....................Hot gas bypass!!! Here's the first piece of sketchy info I've had so far. See attached pdf. Further details to be sent from manufacturer.

Thank you - where do I collect my prize :)

So you then you also need head pressure control.

What about the cooling and heating operating ranges? Hot gas bypass won't stop the system tripping on head pressure. There likely has to be something in the controls that checks to be sure the ambient is low enough for heating mode operation without overloading the system.

[DTLarca]

And the winner is.....................Hot gas bypass!!! Here's the first piece of sketchy info I've had so far. See attached pdf. Further details to be sent from manufacturer.

The drawing shows the TEV feeding the coil suction header and the superheated suction leaving the evaporator through the distributor capillary tubes - I wonder why it seems that way?

You would need to be sure the distributor nozzle and tubes can handle the extra load of a hot gas injection otherwise you could actually worsen the crashing suction scenarios.

You may find yourself preferring to install a post evaporator hotgas injection but using the same TEV to desuperheat the hotgas simply by moving the TEV bulb further downstream along the suction.

[DTLarca]

There's no 4 way valve? No TEV bypass for reverse mode? No TEV for the outdoor coil? No suction accumulator?

[Willsmithiraq]

There's no 4 way valve? No TEV bypass for reverse mode? No TEV for the outdoor coil? No suction accumulator?

Finally......someone see's that I'm up against!!:)

This is the type of information I get out here all the time. The items you mentioned are in at both ends for heating/cooling cycles.

The arrangement of the suction header and the distributor is also wrong on the attached drawing. It's all @rse about face!!

Italians eh!!

[Willsmithiraq]

So I should T into the discharge line anywhere before the condenser. Am I reading that correctly??

[DTLarca]

So I should T into the discharge line anywhere before the condenser. Am I reading that correctly??

Indeed - pretty much anywhere.

You want to come off the top of the discharge line so that your oil isn't collecting in an inactive bypass line.

How far does your bypass run have to go to meet the injection point intended?

[Gary]

So I should T into the discharge line anywhere before the condenser. Am I reading that correctly??

Before the reversing valve.

[Gary]

That diagram is not a reversing system... so not all that helpful.

[Willsmithiraq]

Attached is a pic of the unit. So tapped into the side of discharge just after those service ports will do nicely then!! Any considerations to make about the oil when coming off the side of the pipe as DTLarca mentioned!!

[Willsmithiraq]

Oh yes and the bypass line will be about 6 metres in length.

[DTLarca]

Attached is a pic of the unit. So tapped into the side of discharge just after those service ports will do nicely then!! Any considerations to make about the oil when coming off the side of the pipe as DTLarca mentioned!!

6m is not too far. But you want the hot gas bypass valve as close to the compressor as possible so as to avoid hot gas condensing in the bypass line when it is idle which will cause a flood back when it becomes active.

If you come off the side of the rising discharge pipe try go up then back down as in an inverted trap to prevent any condensed liquid falling back to the compressor discharge but with the hgbp valve close to the compressor - this liquid issue would be of little concern - but preventing oil from settling in an inactive bypass line would be a benefit.

I agree with Gary that the bypass Tee would be better taken of before the 4-way but I don't think there would be any problem coming off after the 4-way.

[Willsmithiraq]

Now looking at the list of what the supplier is sending, I'm getting 2 solenoid valves. One 3/8" for the HGBP and one for the liquid line which is 3/4". Is that correct, if you look at the pdf file it is labelled "VSL".

So as the pressure falls to the setpoint the liquid line solenoid closes and HGBP valve opens, and vice versa as the pressures fluctuate, is this the desired setup??

[DTLarca]

Now looking at the list of what the supplier is sending, I'm getting 2 solenoid valves. One 3/8" for the HGBP and one for the liquid line which is 3/4". Is that correct, if you look at the pdf file it is labelled "VSL".

So as the pressure falls to the setpoint the liquid line solenoid closes and HGBP valve opens, and vice versa as the pressures fluctuate, is this the desired setup??

Normally the liquid line solenoid valve is used for pump down. This is a 4-way reversing valve system so pump down seems meaningless.

Then if you have a hot gas bypass valve on a pump down system you also need a hot gas bypass solenoid valve so that the hot gas bypass valve does not kick in a prevent a pump down or cause continuous pump down recycling.

My first thoughts are that you do not need either solenoid valve.

[Gary]

I think before anything else is done, we need to confirm proper airflow. I would very much like to see wetbulb and drybulb temps before and after the coil.

[DTLarca]

I think before anything else is done, we need to confirm proper airflow. I would very much like to see wetbulb and drybulb temps before and after the coil.

Gary wants to determine the ADP and SHR :)

[Willsmithiraq]

Before the reversing valve.


Normally the liquid line solenoid valve is used for pump down. This is a 4-way reversing valve system so pump down seems meaningless.

Then if you have a hot gas bypass valve on a pump down system you also need a hot gas bypass solenoid valve so that the hot gas bypass valve does not kick in a prevent a pump down or cause continuous pump down recycling.

My first thoughts are that you do not need either solenoid valve.

This is thel list of bits being sent

1 No 010554 ¾ T to ½ Branch
1 No 010607 ½ to 3/8 Reducer
1 No 010571 1 3/8T to 7/8 Branch
1 No 010612 7/8 to 3/8 Reducer
1 No 021844 3/8 Solenoid Body
1 No 021856 7/8 Solenoid Body
2 No 010615 7/8 to ¾ Reducer
2 No 021900 Actuator Coil for Solenoid
1 No 020387 Low Pressure Switch

It seems they are trying to use the low pressure switch to control the aformentioned solenoids? Rather than a dedicated HGBP valve??

HELLLLLPPPPP!!!!!!

[DTLarca]

This is thel list of bits being sent

1 No 010554 ¾ T to ½ Branch
1 No 010607 ½ to 3/8 Reducer
1 No 010571 1 3/8T to 7/8 Branch
1 No 010612 7/8 to 3/8 Reducer
1 No 021844 3/8 Solenoid Body
1 No 021856 7/8 Solenoid Body
2 No 010615 7/8 to ¾ Reducer
2 No 021900 Actuator Coil for Solenoid
1 No 020387 Low Pressure Switch

It seems they are trying to use the low pressure switch to control the aformentioned solenoids? Rather than a dedicated HGBP valve??

HELLLLLPPPPP!!!!!!

Yes, I was thinking about that - you could more easily choke the distributor tubes and actually cause suction to crash doing it that way. I would prefer a single hot gas bypass at the compressor discharge and then a well insulated bypass line up to the injection point.

Both the bypass take off point and injection point should exit and enter from above to prevent oil collection.

You do not want the liquid line solenoid valve. But you could do it with the pressure switch and by pass solenoid valve - so long as you have an accumulator.

[Gary]

Gary wants to determine the ADP and SHR :)

Gary wants to determine air off wetbulb and confirm airflow. :)

[Gary]

Have you checked the blower wheel to see if it is mounted backwards on the shaft?

[Willsmithiraq]

Have you checked the blower wheel to see if it is mounted backwards on the shaft?

Still haven't been back to the unit yet, as I've been fighting fires elsewhere (as usual)!! But I promise it will be the first thing that I will check. I know you don't want to guve up on your air flow ticket just yet.;)

So in the pdf it suggests the valve cut in (opens) at 5 bar and cut out (shuts) at 7 bar. There is an accumulator on the system, so this will just open and close to regulate the suction pressure. Although not ideal this will work??

[Gary]

The end product is the supply air. It must be cool enough and dry enough to do the job. The coil temp is a means to that end. The coil temp must be such that it gives us the correct supply air condition.

What is your target temp/humidity in the kitchen?

[Willsmithiraq]

Target temp inside the kitchen is 25 degrees C and I have no information on the design humidity point (suprise suprise)!!

[DTLarca]

Although not ideal this will work??

He he - I like their courage :)

It can work but I think you need something extra to enable hot gas feed adjustment. You need hot gas but too much will choke the distributor and crash the suction anyway.

You need just the bypass line, which must be insulated, the solenoid valve but then also some means to adjust the hot gas feed to some permanent limit. Like a big needle valve or a little hand expansion valve.

[Gary]

Target temp inside the kitchen is 25 degrees C and I have no information on the design humidity point (suprise suprise)!!

Let's assume we want 25C@50%RH

Refer to this psychrometric chart:

http://www.uigi.com/UIGI_SI.PDF

Find where the vertical 25C line intersects with the 50%RH curve. From this intersection follow the horizontal line to the left until it intersects with the 100%RH curve. The vertical line at this intersection tells us the supply air wetbulb temp should be 14C.

IOW, if the supply air wetbulb is 14C that air when warmed to 25C will be at 50%RH.

But this being a kitchen, we need to offset a heavy moisture load from cooking, washing dishes, etc... so let's lower our target RH to say 40%.

Following the same procedure on the psych chart, our new supply air wetbulb would be about 11C.

[Gary]

I would adjust the HGBV to give me the supply air wetbulb I want... and I don't care what the SHR is. :)

[mad fridgie]

It still concerns me about the high pressure on the heating cycle, even though the paper work is a load of bollocks, it is a reverse cycle system.
Yes hot gas injection will mask the low suction pressure (and is likely to be needed for when cooling loads are low, and I would not do it the way they have), So we have either airflow problems, indoor coil mis application, or a third option 2 types of fault, low load, as covered and a restriction in flow the reverse cycle mode.

[mad fridgie]

NOTE: when testing air flow, temps and pressures, make sure that the coils is FREE of any ice, frosting

[Gary]

It still concerns me about the high pressure on the heating cycle, even though the paper work is a load of bollocks, it is a reverse cycle system.
Yes hot gas injection will mask the low suction pressure (and is likely to be needed for when cooling loads are low, and I would not do it the way they have), So we have either airflow problems, indoor coil mis application, or a third option 2 types of fault, low load, as covered and a restriction in flow the reverse cycle mode.

We can't see if there is a check/bypass around the indoor TXV. This could block the flow in heat mode.

[DTLarca]

Let's assume we want 25C@50%RH

Refer to this psychrometric chart:

http://www.uigi.com/UIGI_SI.PDF

Find where the vertical 25C line intersects with the 50%RH curve. From this intersection follow the horizontal line to the left until it intersects with the 100%RH curve. The vertical line at this intersection tells us the supply air wetbulb temp should be 14C.

IOW, if the supply air wetbulb is 14C that air when warmed to 25C will be at 50%RH.

But this being a kitchen, we need to offset a heavy moisture load from cooking, washing dishes, etc... so let's lower our target RH to say 40%.

Following the same procedure on the psych chart, our new supply air wetbulb would be about 11C.

Nooooo!!!! That's not how we do it!!!! :)

[Quality]

I have enjoyed reading theories for this problem / query but this so called kitchen could in fact have more influence on what is wrong, than the system we are talking about.

Just a tuppence worth of my past nightmares with similar problems

[mad fridgie]

We can't see if there is a check/bypass around the indoor TXV. This could block the flow in heat mode.
Agreed, I suspect that finding the problem would not be that difficult to find, how ever there are times when we are unable to see the wood or the trees. Especially when we trust that the manufacturer to do what we think they should do.
I would suggest that the OP, gets himself a cup of char, sits down and draw the system for himself, a calming way to understand what he is working with.

[mad fridgie]

This is a kitchen, not a data centre, or office block, or kitchen in the Ritz, you have guys and girls working over hot stoves, they just want cooling/heating,they do not care about efficiency, they want dare i say it "wind"

[Quality]

This is a kitchen, not a data centre, or office block, or kitchen in the Ritz, you have guys and girls working over hot stoves, they just want cooling/heating,they do not care about efficiency, they want dare i say it "wind"

No offence I have never worked in a data center or an office and have done almost nil work on air conditioning system which it seems to me you are referring too
I have though worked in just one or two very different types of kitchen which requires

wind as you suggested;)

[Gary]

If all they need is wind, then disconnect the condensing unit, remove the indoor coil and just run the indoor fan.

[mad fridgie]

If all they need is wind, then disconnect the condensing unit, remove the indoor coil and just run the indoor fan.
Heated or cooled, at the moment that have neither:eek:

[Gary]

Okay... let's give them wind that feels really comfortable.

Not too cold, not too hot, not too dry, not too humid... just right. :)

[mad fridgie]

Okay... let's give them wind that feels really comfortable.

Not too cold, not too hot, not too dry, not too humid... just right. :)
Lets just getting heating and cooling, then we can worry about "just right" i think right now they would be happy any sort of right:D

[DTLarca]

But this being a kitchen, we need to offset a heavy moisture load from cooking, washing dishes, etc... so let's lower our target RH to say 40%.

Following the same procedure on the psych chart, our new supply air wetbulb would be about 11C.

Choosing 40% is very arbitrary - why not 45% or 35% or even 30%.

I have attached a psychrometric chart showing two different SHR's being achieved with two different BPF's but each with 11°C WB leaving temps.

[Gary]

Nooooo!!!! That's not how we do it!!!! :)

For better or worse, I do things differently... from just about everyone... lol

[DTLarca]

For better or worse, I do things differently... from just about everyone... lol

Sure but just because one does something differently it does not guarantee that they will be either more or less successful - depending on which side of the notion you are standing. You might very well do it differently but the question remains - will it work - can the means be justified - can its success, if any, be repeated at will :)

[mad fridgie]

I would focus firstly on the mad fridgie,s SHR
MFs SHR = Smiling Happy Reciprient

[Gary]

Choosing 40% is very arbitrary - why not 45% or 35% or even 30%.

The 40% is arbitrary. I have no idea what RH% will be needed to offset the unknown moisture load. Actually, I chose 40% because it is the bottom of the comfort range (40-60%RH).


I have attached a psychrometric chart showing two different SHR's being achieved with two different BPF's but each with 11°C WB leaving temps.

I don't see where they both have a leaving wetbulb of 11C?

[DTLarca]

I don't see where they both have a leaving wetbulb of 11C?

You sure? :)

[Gary]

You sure? :)

Am I sure I don't see it? Yes.

Am I sure you are wrong? No.

[mikeref]

I would focus firstly on the mad fridgie,s SHR
MFs SHR = Smiling Happy Reciprient
MAD, when i read the first line i thought, S--t! Not again! :rolleyes: