Another day another problem

I've been working on 3 heat pump systems each with 2 circuits seperate circuits.

However i'm having problems with system 1 + 2

Systems are 3 years old and have never worked correctly supposedly.

When i first got on site system 1 (circuit 1&2) both had LP faults and no refrigerant in the system, it was obvious others had been working on it.

System 2 (circuit 1&2) again both had no refrigerant in the system, pressure tested and found leaks on all systems and repaired. Vacced out and recharged.

Ran system 1 in heating and system began to pump itself down we looked at the TXV and found that it had been played about with.
After holding the bulb the pressure increased from 1/2bar to 1bar, we had 6k subcooling so i was thinking that a new TXV was needed.

I decided to put into cooling to prove the system would work if that TXV wasn't being used however after a few mins of running circuit 2 head pressure began increasing slowly until it got to 26bar and tripped.

On the condensor there is ductwork that comes off the top in order to reroute the air out of the room (the condensor is insidea building)but the ductwork doesn't have an inline fan to push the air along.

I thought this may be the problem so we took the ductwork apart so the air off blew into the room, this brought the HP down to 15bar where it stayed.

We tested several times replacing the ductwork and the pressure would rise, then we would take the ductwork off and the pressure would fall...to me proving that the ductwork is causing it to go off on HP.
But if that was the case then surely circuit 1 would be going off on HP as well which it wasn't, circuit 1 was running away happily with no problems.

System 2 circuit 1 is doing exactly the same and its got me baffled and it's been a long day!!

This should be a simple fault to fix but maybe it isn't just the 1 problem.

To Recap
System 1 circuit 2 on cooling faults HP
circuit 2 on heating faults LP

System 2 circuit 1 on cooling faults HP
circuit 1 on heating faults LP

As you have found out, the increased resistance of the ductwork results in a drop of airflow over your coil.
When it's in heating, the coil is acting as the evaporator, so low air flow = low heat absorbed and hence, low suction pressure - past the point of LP trip in this case.

When it is working in heating, the coil is acting as the condenser, and a low air flow causes insufficient heat to be rejected, resulting in high pressures and an HP trip.

With only 1 circuit in operation, the air flow from the fan may be sufficient to absorb/reject sufficient heat to prevent the safeties from operating.

The solution is to uprate the fan with a model that can cope with an increase in static resistance, thereby allowing the design airflow over the coil. Some manufacturers offer a direct replacement fan with a larger motor for such occasions. If you cannot get a manufacturers replacement, you can always add a seperate inline fan and may be think of adding some sort of speed control to it, possibly with a pressure transducer/controller or even a normal HP control such as the one made by Aspen.

Hi Frank, on condenser 1, circuit 1 when running alone works fine in both heating and cooling regardless of the ductwork.
Circuit 2, in cooling faults on HP and removing the ductwork does help and brings the discharge Pressure down to 15b....indicating airflow like you suggested.
In heating circuit 2 drops to 1/2bar straight away, it isn't gradual. To me indicating some sort of restriction.

If it was airflow then surely both circuits would be experiencing the same faults which they are not regardless of wether they are run independent or together.

I've spoken to clivet and they say the condenser fans aren't made for being used with ductwork.

It sounds like you have more than 1 problem then.

I would remove the ductwork to trouble shoot and get the circuits/systems operating as they should be, then you can re-fit the ducting and see what effect that has on system performance.

Check your gas charge as a first step.

What are the air in and air out temps?

Unless/until the airflow problems are resolved, you cannot accurately identify other problems, because the pressures/temps throughout the system are distorted by the lack of sufficient airflow.

Air in15C/Air out 23C with the ductwork connected.

We removed the ductwork today on system 1 and fitted a new TXV on the outdoor unit. The system now works on heating and with the ductwork removed also works on cooling.

System 2 looks like another TXV & drier is also needed.

Then we ran up system 3 and found the same problems.

The systems are only 3 years old but are in such a bad state, supposedly they have had all sorts of "tradesmen" trying to fix them.

23-15=8K dT

This does not indicate an airflow problem. Rather it shows extremely light load. Presumably because of the faulty TXV?

I agree, it does not indicate an airflow problem, all i know is when the ductwork is removed the head pressure drops.

I took that temp when the discharge pressure was around 17bar, when i go back monday i will also take a temp when the pressure has increased and is ready to trip off.

The faulty TXV was changed on the outdoor unit (heating mode)

In cooling mode the TXV is in the indoor unit, if this TXV was also faulty surely the circuit would be showing LP alarm before it went off on HP.

Another thing i noticed is the bulb for the TXV's are mounted vetically even though Danfoss recommend to mount them horizontal. What effect could this have on the TXV?

Quote:

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Originally Posted by marc5180

all i know is when the ductwork is removed the head pressure drops.

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This does indicate that the ductwork is having an effect on the amount of air that the fan can move (increased static resistance)

Once you have the systems operating correctly, then you need to address the fan problems. Increased head pressures = increased compressor temperatures = reduced compressor lifespan and increased running costs. Plus, reduced refrigerating effect.

You can mount the bulb vertically (though horizontal is prefered) so long as the thin tube comes out the top, if its the other way it can make the valve slow to respond as it has to push liquid down the tube or suck it back etc.

Sounds like you have a bit going on there Marc , How long and how big is the ductwork ,how many bends etc ,what is the free area of the external grille or louvre ,you say in the original post the air has to be routed out of the room is there an adequate volume of air being introduced into the area the condensers are located via fans or transfer grilles.As Frank says increased static pressure on the exhaust side certainly wont help. if you leave the duct connected and remove the louvre does the head pressure drop off.
You have probably checked all that already.

Cheers Stu

Quote:

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Originally Posted by marc5180

I agree, it does not indicate an airflow problem, all i know is when the ductwork is removed the head pressure drops.

I took that temp when the discharge pressure was around 17bar, when i go back monday i will also take a temp when the pressure has increased and is ready to trip off.

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Assuming R22, this would put the SCT at about 47C, with air in temp at 15C, that gives us 47-15=32K TD. That's huge. This would point towards either non-condensibles or gross overcharge.

I'm thinking this would be a lot easier if we knew all of the temps/pressures throughout the system. Trouble shooting is easier with complete information.

make sure the txv bulb is mounted lower than the head, and the bulb is insulated to ensure response to loading and is not affected by ambient air and ensuring liquid is in the sensing bulb not the head of the txv

Quote:

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Originally Posted by frank

This does indicate that the ductwork is having an effect on the amount of air that the fan can move (increased static resistance)

Once you have the systems operating correctly, then you need to address the fan problems. Increased head pressures = increased compressor temperatures = reduced compressor lifespan and increased running costs. Plus, reduced refrigerating effect.

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With the ductwork off the fans don't seem powerful enough to move the air along and out of the ductwork, i checked that they weren't running backwards which they werent.
I'm going to remove the ductwork and then address the other problems first

Quote:

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Originally Posted by monkey spanners

You can mount the bulb vertically (though horizontal is prefered) so long as the thin tube comes out the top, if its the other way it can make the valve slow to respond as it has to push liquid down the tube or suck it back etc.

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Thanks Jon, the valve is mounted with the thin tube coming out of the top. Danfoss say to mount the bulb horizontally which is what threw me off.

Quote:

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Originally Posted by stufus

Sounds like you have a bit going on there Marc , How long and how big is the ductwork ,how many bends etc ,what is the free area of the external grille or louvre ,you say in the original post the air has to be routed out of the room is there an adequate volume of air being introduced into the area the condensers are located via fans or transfer grilles.As Frank says increased static pressure on the exhaust side certainly wont help. if you leave the duct connected and remove the louvre does the head pressure drop off.
You have probably checked all that already.

Cheers Stu

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Hi Stu, the ductwork that comes off the condensors is about 600-800mm square (not exactly sure of the size.) Inside the room where the condenser are the ductwork ranges from 3m-6m of horizontal before it goes up through the roof about 5m and then on the roof they have another piece of ductwork that has been made up and comes off the roof on a right angle.

In total there are 3-4 bends on the ductwork off each condenser and there are also dampers (turning vanes) inside each bend which are all open.

The room is quite large but there doesn't seem to be any air being introduced into the room by means of fans. We did question this at first but assumed if the airflow wasn't enough then all systems would be tripping on HP.


The ductwork is also not supported properly so taking it apart is a bit of a task. We had to use prop stands to support the ductwork on condenser 1 to be able to remove the first bend.

Quote:

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Originally Posted by Gary

Assuming R22, this would put the SCT at about 47C, with air in temp at 15C, that gives us 47-15=32K TD. That's huge. This would point towards either non-condensibles or gross overcharge.

I'm thinking this would be a lot easier if we knew all of the temps/pressures throughout the system. Trouble shooting is easier with complete information.

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Hi Gary,
The systems are running on R407c and there are no noncondensibles present since the gas is freshly charged. Both circuits have the same amount of refrigerant in and circuit 1 is running fine with 7k subcooling and 5k superheat with good air off temps.

The only problem with the pressures i am giving are that they are not stable with the ductwork on and just keep increasing.

When i go back tomorrow i will give a full list of figures with the ductwork on and ductwork off.

Quote:

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Originally Posted by install monkey

make sure the txv bulb is mounted lower than the head, and the bulb is insulated to ensure response to loading and is not affected by ambient air and ensuring liquid is in the sensing bulb not the head of the txv

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Hi Install monkey, yes the bulbs are mounted lower than the valve itself but they weren't insulated properly so we insulated them all the other day.

Went back to site today and changed the TXV on unit 1 and 2, in order to give them some heat, I left the duct work off and took the following figures:

Discharge pressure 14.2 bar/32.8
Suction pressure 2.75 bar/-13.8
Actual suction temp 1C
SH 15k
SC low
Liquid line temp 32.6C
Evap (outdoor unit air on) 7.9C
Evap air off -1.3C
Condenser (indoor unit) air on 16.8CCC
Condenser air off 25C

The outdoor unit discharges the air off into the room which obviously is affecting the air on.
The compressor discharge temp varies between 40-50 degrees and does not get any higher, by the time it gets to the indoor unit the max air off I have had, is 27 degrees.

How can I get the discharge temp to increase? Or is it down to the low air on, of the indoor and outdoor?

Quote:

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Originally Posted by marc5180

Went back to site today and changed the TXV on unit 1 and 2, in order to give them some heat, I left the duct work off and took the following figures:

Discharge pressure 14.2 bar/32.8
Suction pressure 2.75 bar/-13.8
Actual suction temp 1C
SH 15k
SC low
Liquid line temp 32.6C
Evap (outdoor unit air on) 7.9C
Evap air off -1.3C
Condenser (indoor unit) air on 16.8CCC
Condenser air off 25C

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The evap airflow is not insufficient.
The cond airflow is not insufficient.
The SC is low.
The SH is high.

Add refrigerant until the SC is 5.5-8.5K or the sightglass clears, whichever comes first.

Take all new readings.

Even undercharged, the cond TD is high. The liquid line temp is nearly identical to the SCT, therefore noncondensibles are not the problem, nor is overcharge. Possibly the indoor coil is grossly undersized? If it is, then we would expect very low suction pressure in cooling mode.

On cooling the sightglass does clear for about 15 seconds but on heating the sight glass is constantly flashing indicating lack of charge.
These figures change quite a lot for example just after i had taken these readings the Suction pressure had increased to 3bar/-12 and the actual temp was -10 plus with the discharge temperature/ discharge superheat being so low i thought this indicated overcharge.

As I recall, you said there are multiple indoor coils on this unit. Did you check the operation of both indoor coils?

Are there check valves bypassing around the TXV's? Are these installed in the correct direction? The arrow on the side should point in the direction opposite the TXV direction.

On each outdoor unit there are 2 circuits that each feed a coil in 1 indoor unit. 3 outdoors, 3 indoors 6 circuits.
On the 2 outdoors that I ran up today (4 circuits) they all had similar symptoms and not one of them had air off on the indoor on heating of more than 27C.
They ranged from 21-27C air off.
There are check valves installed near the txv and they are installed the right way.

If they were short of refrigerant then surely the comp discharge would be high which it isn't

Quote:

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Originally Posted by marc5180

On cooling the sightglass does clear for about 15 seconds but on heating the sight glass is constantly flashing indicating lack of charge.

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An improperly installed or sticking check valve on the indoor coil could cause liquid to build up in the coil since it's only path would then be through the TXV... backwards.

Quote:

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Originally Posted by marc5180

If they were short of refrigerant then surely the comp discharge would be high which it isn't

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Generally, discharge temp goes hand in hand with compressor inlet superheat. If the compressor inlet SH is lower than the evap outlet SH, then liquid is being added along the way, which would indicate a leaking reversing valve.

I find inlet SH to be a much better indicator than discharge temp.

Quote:

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Originally Posted by marc5180

I've spoken to clivet and they say the condenser fans aren't made for being used with ductwork.

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That's true. Propellor fans can't pump against a static pressure. Squirrel cage fans made ducted systems possible.

Got back to site yesterday and found the compressor on condenser 2 circuit 1 heavily iced *and every 10mins or so would sound very noisy and the discharge temp would drop 10degrees plus, to me indicating floodback but the superheat was 5k..
On condenser 1, (the unit that i took the readings from on monday) the sight glass is always flashing, tried adding additional refrigerant but this made no difference to the sight glass, the readings I got fluctuated so much that they didn't make sense. I even began to doubt my temp sensor was reading the right figures.

At 1 point I was getting readings of 10k subcooling then within 5 mins this drops to minus1, sh was always constant at 5k.

*To try and raise the discharge temp I adjusted the txv to increase the suction superheat but this didn't alter no matter if the valve was adjusted the superheat always stayed the same 5k.*

I took the ductwork off each condenser and this did have an impact.
None of the compressors were freezing up and were sweating nicely and the compressor that was making the noise began to run much quieter.

None of the units trip on hp anymore but there is one unit that still trip on low pressure at 2.3 bar because the suction pressure us so low.

The *suction pressure on all 6 circuits vary between 2 -3 bar max

With the amount of hours you've spent on it at this stage it woulda been cheaper to refit new gear :)

How do you know how many hours i have spent on it?:off topic:

Quote:

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Originally Posted by marc5180

I took the ductwork off each condenser and this did have an impact.
None of the compressors were freezing up and were sweating nicely and the compressor that was making the noise began to run much quieter.

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I'm getting confused here. If this is in heat mode, then the outdoor coil is the evaporator, not the condenser... so the ductwork is on the evaporator, right? Or the indoor coils are also ducted?

Appologies, i should have said the outdoor unit not the condenser.
The ductwork is on the evap in heat mode, the indoor coils are large floor standing units but not ducted.

And the previous post was about heat mode, right?

Yes they are in heat mode.

Did you take new temp/pressure readings?

I added refrigerant to try to increase the subcooling which at one point got to 10k but then after a few mins i measured it again and got -1k. The readings i got weren't stable and changed from undercharged to overcharged frequently.

I understand how to troubleshoot the refrigerant circuit in theory very well but in practice the readings i seem to get never seem to make much sense.

When you take readings Marc, they should be taken at near "design conditions" not during pulldown. As your systems are trying hard to get to design, the readings will fluctuate, as you are seeing.

Where your compressor is getting floodback, this indicates that the evaporator (outdoor coil in his case) is not absorbing sufficient heat to " evaporate" the liquid refrigerant. This can be caused by the Evap fan not pulling sufficient airflow over the coil (blocked filters) (poor fan duty) (dirty coil) or the TEV overfeeding, or lack of heat load.

When you added additional gas, you probably over charged it, trying to compensate for some other latent problem.

I would suggest that you recover and recharge as a first step to make sure that the charge is right before you go any further.

When it is recharged, let it settle for 15 minutes then take some readings and post them so we can see where the system is at.

Regardless of what other problems are found, I think everyone will agree that those outdoor units should be... outdoors.

With those units indoors and the ductwork removed, the room they are in will become a deepfreeze in the winter and an oven in the summer.

With the ducts installed, there will be insufficient airflow.

If the units cannot be moved outdoors, I would suggest a big exhaust fan at one end of the room and a big intake at the other end of the room, in effect bringing the outdoors into the room.

These airflow problems are going to drive the system crazy and make everything else impossible to troubleshoot.

Hi Frank, the charge is now correct because i removed the additional refrigerant that i had added in order to clear the sight glass.
I understand that the system should be at design temperature but the problem is it doesn't get up to design temperatures.
I tried increasing the HP to get the SCT to 40C and then took measurements but again the figures i got were confusing and definatly weren't stable.
I kept taking different readings throughout the day and none of them made sense.
Maybe i'm doing something wrong.

Gary, the ductwork is going to be removed and we are going to put and exhaust and an intake fan in order to get the required air changes into the room.
Then when it is done i will be going back to check it, in the meantime i'm going to get my digital thermometer calibrated, just in case.

Stick with it mate. Its not a race.
Slowly slowly catchy monkey.
You have inherited someone elses **** up.
Think of the satisfaction when you walk away knowing its how it should be.
Cheers.
Stu

Quote:

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Originally Posted by marc5180

Gary, the ductwork is going to be removed and we are going to put and exhaust and an intake fan in order to get the required air changes into the room.
Then when it is done i will be going back to check it, in the meantime i'm going to get my digital thermometer calibrated, just in case.

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Hopefully the units are not blowing air at each other and all will be blowing air towards the exhaust fan.