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 . 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
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!!!!! 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?
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?
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?