Strage Pipework Configuration

[marc5180]

Evening chaps,

I got called out to an air handling unit today that wasn't working due to a compressor that was 'down to earth'.

Whilst i was there i looked at the pipework and couldn't figure it out.

The system is a reverse cycle heat pump and so has a 4 way reversing valve but only 1 electronic expansion valve.

The thing i was struggling with was - the liquid line into the expansion valve came from both coils into a common liquid line, into the expansion valve and then out and into the top of both coils so in effect both coils were getting cooling. There is none return valves in the pipework but they allow flow into and out of both coils.

Yet also one coil would be getting heat depending on the mode so how can this work.

See picture below

[install monkey]

if it has worked previously then it should be ok,is the drier bi flow?-it should work -whose kit is it?

[chillerman2006]

Hi Marc

I would draw out the pipework configuration and include NRV direction & I think it will all fall into place mate

If not upload the drawing and will work through it with you

You have said it works when switched from heat/cooling

So I presume (maybe wrongly) that the additional pipework is to aid recovering refrigerant from one side to another, to aid in switching heat/cooling vice versa quicker

R's chillerman

[install monkey]

maybe send marc some crayons so he can colour it in?

[marc5180]

This is the thing, it's only 3 months old and a compressor has gone down. It's my first visit to the site and have never seen these units actually work but can only presume they must have.

[chillerman2006]

Whats make model ? mate

Can try to find flow chart or someone might have one

[airconadam]

Hey guys,

Were the expansion device is on the top of the picture and were its lagged,

so if this sytem is on cooling the evap is on the left which goes through the metal cover and the condenser is on the right,

When this is on cooling we also get saturated liquid going down the lagged line into the evap BUT also going back into the condenser???

When on cooling this lagged pipe is 8 deg c throughout,

Adam

[marc5180]

Hi Marc

I would draw out the pipework configuration and include NRV direction & I think it will all fall into place mate

If not upload the drawing and will work through it with you

You have said it works when switched from heat/cooling

So I presume (maybe wrongly) that the additional pipework is to aid recovering refrigerant from one side to another, to aid in switching heat/cooling vice versa quicker

R's chillerman

I've drawn it out and it doesn't make sense. How can a coil produce heating if there is also a low pressure,saturated liquid/vapour mix going into the coil?? Unless it is acting as a liquid/suction heat exchanger i.e superheating the suction and subcooling the liquid.

I didn't say it worked when switched from heat to cool because the compressor had failed. Maybe there is a simple explanation and i'm missing something

[chillerman2006]

Hi Adam

still none the wiser mate, dunno if marc understood what affect this has

can you hit us with that again with more detail mate

R's chillerman

[airconadam]

Also there is 4 of these units on site as marc says they are only 3 months old!!

and only 3 out of the 4 are actually working due to failed compressors!!!

Adam

[marc5180]

Its from a company in manchester that make them to order, it's not possible to get piping specifications unless i speak to them direct which i will on Monday.

[chillerman2006]

What I am thinking mark is whilst you have a higher pressure in the condensor than the liquid line the NRV allows that refrigerant to mix with the liquid line on switch over to heating, enabling a faster change from cooling to heating and then vice versa when switching from heating back to cooling....the nrv's are pressure controlled check valves

[install monkey]

air handlers-by any chance-if theyre only 3mth old then theres warranty i assume-surely u just have to point out whats f****d haha

[airconadam]

Hey chillerman,

no worries

I will try but its difficult trying to explain over writing,and always difficult when looking at pictures like that,

anyway, on cooling the discharge goes into the right coil (condenser) on the middle pipe which isnt lagged below that at the bottom right of the pic is the liquid,

you can see were it goes up through the filter drier through the sight glass then onto the expansion valve, this is all ok but after the exp valve, the saturated liquid should surely only go to the evap through the metel sheet?

In this case as it comes out it goes into the evap, and also the nrv is also directed so it goes back into the condenser onto the right??

If you look at the picture were i have ripped the lagging to reveal the nrv's they both point outwards to the edge of the screen,

hth

Adam

[marc5180]

air handlers-by any chance-if theyre only 3mth old then theres warranty i assume-surely u just have to point out whats f****d haha

Yeah i have done but i still want to understand it mate, which is why i'm not an install monkey

[marc5180]

The arrows are the directions of the non return valves.

We have 3 pipes going into each coil and the way the non return valves are positioned then each coil uses all 3 pipes in each coil.

[chillerman2006]

Irrelevant

[al]

Are all the units piped this way, ie is the NRV backwards?

al

[chillerman2006]

Evening Al

you know this kit better than me mate

are these bypass check valves for cooling/heating switch over ?

or have I missunderstood this setup ?

R's chillerman

[al]

Also when the eev shuts it will act as an NRV.

On a site last year i found some airedale heat pumps piped wrong in the factory.

al

[yinmorrison]

The discharge pipes must go through the plate and tee into the expansion line after the eev but that is not shown so presumably there is no access to see that. Therefore when a coil is used as the condenser the high pressure vapour cannot go back through the NRV and into the EEV outlet and so the liquid refrigerant will only pass through the EEV and go to the cooling coil as the pressure on the other side of the NRV on the condenser side is higher.

[marc5180]

Yes i understand what your saying, our initial thought was the NRVs were in the wrong way round but even if they were turned round then i still can't see how it could work.
The position the NRVs are in then they serve no purpose as they don't prevent liquid from entering the coil as far as i'm aware.

[yinmorrison]

Marc the NRV's are required , if you take them out you will bypass hot gas into the expansion line of the coil doing the cooling.The refrigerant in the expansion line will take the path of least resistance so the NRV effectively is stopping the discharge gas from short circuiting.

[chillerman2006]

The discharge pipes must go through the plate and tee into the expansion line after the eev but that is not shown so presumably there is no access to see that. Therefore when a coil is used as the condenser the high pressure vapour cannot go back through the NRV and into the EEV outlet and so the liquid refrigerant will only pass through the EEV and go to the cooling coil as the pressure on the other side of the NRV on the condenser side is higher.

Hi Yin

the lagged tube is liquid line after eev then ?

and at suction pressure ?

R's chillerman

[yinmorrison]

You got it Chillerman.

[chillerman2006]

Thanks Yin

So some made up figures to make it easier to understand

we have 10 bar discharge & 4 bar suction

the lagged tubework and which ever coil is currently the evaporator are at 4 bar

the nrv is open at equalised pressure to the current evaporator

the heating/condensing coil is at 10 bar at a higher pressure

so the nrv prevents high pressure vapour/liquid entering the low pressure liquid feed to evaporator

Nice one Yin

R's chillerman

[yinmorrison]

Marc, I would suggest the problem you have with these AHU's is that there is only the one EEV. If you assume ( never do that myself !! ) that the coils are sized so that one is selected as the evaporator and one the condenser then how can the SH be set up to cover the different size coils , you will almost certainly have the EEV set correctly for one of the coils and therefore either way when the other coils is used as the evap you will have too little or too much SH, I suggest you take this up with the AHU Manufacturer before losing more compressors.

[marc5180]

The plate was pot rivotted on so i was unable to lok behind it at the pipework- i did try.
So the NRVs are pressure controlled?
In other words when the discharge pressure goes through the coil and tries to come out on the liquid line (heading towards the EEV) this puts pressure on the NRV and prevents the liquid coming from the EEV from passing through the NRV into the coil even though the directional arrow shows that it should pass through

[yinmorrison]

Thats it Marc , because it is on the expansion line so at lower pressure on EEV outlet and cannot pass through NRV due to high discharge pressure on other side of it , I still say its the single EEV that is the problem unless of course the EEV control system alters when the system is reversed to take account of the different coil sizes.

[marc5180]

The compressors are copeland digital scrolls and the superheat is controlled by a dital ED3C?? emerson controller that constantly monitors the superheat and adjusts it accordingly.

[chillerman2006]

Yin

also when switching from heating to cooling what is stopping the condensor now evaporator from allowing liquid back to the compressor, as I dont see an accumalator, or there also one hidden behind this plate ?

If not my thinking is liquid coming back will take the compressors out, if its a superheat problem....Marc is there any sign of high temps at compressors - paint cracking, I have seen these copelands run very hot without failure & can also take liquid, but not if enough liquid passes to wash out the oil....was the oil level ok ?

R's chillerman

[yinmorrison]

Not familiar with the Emerson but it still looks like a superheat problem so hope you can sort it out Monday best of luck , I am off to Pub now for a couple of the black stuff : ) Have a guid night.

[al]

Marc

Assuming the factory have piped correctly, how many compressors have failed on this unit?

al

[marc5180]

Yin

also when switching from heating to cooling what is stopping the condensor now evaporator from allowing liquid back to the compressor, as I dont see an accumalator, or there also one hidden behind this plate ?

If not my thinking is liquid coming back will take the compressors out, aswell as an unbalanced system in one mode or the other using only one eev

R's chillerman

Good point Chillerman. Think i'm going to have to try and speak to the manufacturers but how the heck to i begin to explain it?
I'll post back on monday if i manage to get any answers.

Thanks everyone who helped out (even you install monkey)

[marc5180]

Hi Al, there is only one compressor in each AHU and so far 2 AHU's have failed out of 4 with another one of them suspected not working (although this hasn't been confirmed yet).

[al]

ok, did you commission them, are air flows correct for the units and have you operating data from one of the other units to confirm superheat etc, what sort of capacity are they?

al

[marc5180]

No i didn't commission them, they were commissioned by the manufacturer. Again i can only assume the airflows are correct until i see the commissioning sheets.
The guy who had them wasn't in today but will be next week.

[al]

Is it the customer or manufacturer that is paying you?

al

[marc5180]

The customer because the manufacturer wasn't able to get there for a few days

[al]

That makes it a bit easier, can't imagine the customer is too impressed!!

Can you say who made the units?

Did compressors burn out or are they locked rotor?

alec

[chillerman2006]

Morning Marc

Still thinking about your system

As can not see whats there

If no CPR is fitted maybe you would like to suggest installing one

Aswell as an accumalator, to assist keeping the new compressors safe

R's chillerman

[install monkey]

any alterations to the system needs approval from air handlers otherwise warranty void!!! and if pots are only lasting 3months ur gonna need that warranty

[chillerman2006]

any alterations to the system needs approval from air handlers otherwise warranty void!!! and if pots are only lasting 3months ur gonna need that warranty

Install

What would you expect to be the cause here of compressor failure, you must see a few of these ?

Also that was why I said ''suggest'' meaning to manufacturer as they have failed to build a reliable system

The Compressor pictured does not appear to have been cooking, possibly liquid return, washing the oil out

R's chillerman

[install monkey]

no crankcase heater on the pot, system is within the airflow so exposed to 10-40deg ambient, no jacket on the compressor, as u say no suction accumulator or evap press reg, as with air handling units normally 100% fresh air then sticking a cooling coil in there there is not a constant load so theyve done well sticking an electronic expansion valve-at least it will be more responsive, also them check vavles will need checking to ensure theyre not passing as with the 4 way valve as its too easy to chuck a pot in and watch it destroy itself, also i would look at the control strategy, comp restart delat, setpoint differential it should have a free cooling setpoint that usually is set around 16 deg which will stop the mechanical cooling and rely on fresh air.
are the v belts ok,if fitted,panel filters blocked as they normally last 3mth also check alarm history, is there a lp swith on it or transducer, may be sartup of the compressor causing pipework to flex and the lp being auto reset??
are the fans inverter driven whats the minimum speed or is it controlled of duct pressure?
i could nip up to site as its in my hood!!haha

Install

What would you expect to be the cause here of compressor failure, you must see a few of these ?

Also that was why I said ''suggest'' meaning to manufacturer as they have failed to build a reliable system

The Compressor pictured does not appear to have been cooking, possibly liquid return, washing the oil out

R's chillerman

[mad fridgie]

At the beginning.

liquid feeds the expansion valve "EEV", after the EEV, the pressure is higher than the suction and lower than the discharge. the flow will travel to the evap, you can not have discharge pressure flowing back into the valve, because of the check valve (in either operation heat or cool)
Inside i would suggest that the EEV lines are joined to the bottom pipes.
These bottom pipes each have little check valves (you can see one by the sight glass).
These small lines feed into a common receiver, ensuring a liquid seal for the EEV.
Your compressor are likely to be seizing due to oil dilution, increase superheat setting, or add an accumulator after the EEV pressure and temp sensor

[marc5180]

Just sent you a pm Al, the customers not too impressed, especially since the compressors will take 3 weeks to arrive.
1 of the compressors had a resistance to earth on each of the windings of 150 ohms and kept tripping the breaker upon start up.
Not too sure about the other 1 but it looks like it's soft pumping.

[chillerman2006]

At the beginning.

liquid feeds the expansion valve "EEV", after the EEV, the pressure is higher than the suction and lower than the discharge. the flow will travel to the evap, you can not have discharge pressure flowing back into the valve, because of the check valve (in either operation heat or cool)
Inside i would suggest that the EEV lines are joined to the bottom pipes.
These bottom pipes each have little check valves (you can see one by the sight glass).
These small lines feed into a common receiver, ensuring a liquid seal for the EEV.
Your compressor are likely to be seizing due to oil dilution, increase superheat setting, or add an accumulator after the EEV pressure and temp sensor

Evening Mad

If you was to add an accumalator to this system, what sort of size would you go for ?

R's chillerman

[marc5180]

At the beginning.

liquid feeds the expansion valve "EEV", after the EEV, the pressure is higher than the suction and lower than the discharge. the flow will travel to the evap, you can not have discharge pressure flowing back into the valve, because of the check valve (in either operation heat or cool)
Inside i would suggest that the EEV lines are joined to the bottom pipes.
These bottom pipes each have little check valves (you can see one by the sight glass).
These small lines feed into a common receiver, ensuring a liquid seal for the EEV.
Your compressor are likely to be seizing due to oil dilution, increase superheat setting, or add an accumulator after the EEV pressure and temp sensor

Morning MF, I was hoping you would pop in

I was thinking last night about the other AHU's from the same manufacturer that we look after and they do have accumulators fitted.
I began to think about this system and it must have one fitted, if you look at the suction coming off the 4way rv, that then goes into the accumulator and then back out into the suction of the compressor.

[marc5180]

Evening Mad

If you was to add an accumalator to this system, what sort of size would you go for ?

R's chillerman

Chillerman,
A suction line accumulator should be sufficiently sized to hold the entire charge of the system.

[install monkey]

a liq reciever should be able to hold the full system charge an accumulator only needs to accomodate any liquid that hasnt boiled of in the evap thus ensuring only vapour returns to the compressor http://www.stara.co.kr/parker_catalo...og/40-10-7.pdf