New system tripping on low pressure??

[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!.. 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

[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

[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!