Swimming Pool Heat Pump

I went to a call on swimming pool heat pump system, which was icing up.

When I got there, it was switched off and after only a couple of minutes of running it iced up from the TEV to the evaporator. Client said that was exactly what it was doing before. I wanted to prove it was gas charge/leak, so I added a very small amount of refrigerant to see what happened. Literally a gauge line of R22, cleared the iced all the way to the distributor, another line cleared the distributor. At this point i´m thinking, that it must have a small leak somewhere. I left it running for an hour, and everything seemed to working. Went to get the leak detector from the van, and when I got back it had stopped. It restarted again, a minute or so after then tripped 5 or so minutes later, while I was trying to find out what was causing it to trip it must have started an stopped 5 or 6 times. There is only a suction service port nothing else so only one place to take a pressure reading. Safety devices are HP, LP, Water flow, and low ambient temp.

I went back yesterday, armed with a line tap valve, which I was going to put on the discharge stub for the HP switch. Get a reading, then braze up once I knew what the problem was. It didn´t trip once yesterday, I ran it for 2 hours non-stop while I was there, and it´s still running now. So I don´t know what was causing it. I think It may have been HP, but I can´t prove that.

Here´s some readings I got yesterday,
Ambient air temp: 19ºc
Suction Pressure: 57psi
Discharge Pressure: 275psi
Suction Temp (at TEV bulb): 1.3ºc
Discharge temp (Compressor): 77.3ºc
Liquid line temp (off condensor): 23.8ºc
Water inlet temp: 21.6ºc
Water outlet: 22.4ºc

The unit is 8 years old, no idea on make, model or anything as there are no data plates. I got the gas type (R22) from the compressor label. System has never been worked on before. I´s assured there is good water flow as everything on the water side has tested (apparently). Have I missed anything obvious?

P.s. the line-tap valve will be cut off, it´s just there for test purposes.

Your td of condenser is too small. You should check if condenser is clean and for appropriate water flow.
By discharge pressure it is dirty!
Then take new measurements again.
This time include air off evaporator measurement and make sure that evaporator is clean.

Then you will probably get lower high pressure readings and lower subcooling.
If subcooling is high after that, remove some charge until you have about 5-7K of subcooling.
Then check your superheat at TEV bulb if it is 4K or more!

I agree with nike123, check your condenser. Is there a bounce timer across the flow switch? (eliminate trips due to air bubbles)

Seems that also the evaporator doesn`t absorb enough heat. Superheat is acceptable but the approach of evaporator is a little bit over the limits.
As nike says try to clean also the evaporator heat exchanger.

regards

Thanks for the help. The condenser is sealed, so it´s not possible to clean it. I thought that the water TD was low as well, but I was told once from a pool guy over here, that you don´t get much TD from a heat pump, because of the amount of water that flows through them. I believe you lot more than the pool guy though.

Not disagreeing with you, but why would I have such a good difference across the condenser, if it was dirty? I have almost 54ºc. I would expect to have a high temperature at the liquid line if the condenser wasn´t working. Is this not the case?

The evaporator is air cooled, and it is clean. I already checked that.

By bounce timer, i´m not sure what you mean. At the switch there is an adjustable wheel, which is set at about half way.

The unit tripped twice today, so i´m going to have to take a look at it again,

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Originally Posted by airefresco

Thanks for the help. The condenser is sealed, so it´s not possible to clean it.

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It could be chemically cleaned.

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I thought that the water TD was low as well, but I was told once from a pool guy over here, that you don´t get much TD from a heat pump, because of the amount of water that flows through them. I believe you lot more than the pool guy though.

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You are mixing here two terms. TD is used as measure of temperature difference between condenser water in and condensation saturation temperature. dT is used as measure of temperature difference between condenser water in and out.

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Not disagreeing with you, but why would I have such a good difference across the condenser, if it was dirty? I have almost 54ºc. I would expect to have a high temperature at the liquid line if the condenser wasn´t working. Is this not the case?

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You are having high TD (condenser split) of 29,7K because condenser is not able to reject heat. That is because it is dirty. If you have clean condenser, that TD value should be around 15K. dT of 0,8K is consequence of that low heat transfer at condenser because of dirt. And, when you clean condenser that TD should drop to 15K and, as consequence of that, your condensation saturation temperature should be around 37°C.
That is why you are having high condensation pressure/temperature for that pool water temperature.

So if the condenser is clean, then more heat is rejected, which would then lower discharge pressure/temperature and increase the dT of the water? I should have had a discharge pressure of more or less 190psi? Is that correct? What should I then expect the dT to be (with a clean condenser)?

Thank you for your help. I´ll look into chemical cleaners.

EDIT: Just to clarify, I mean the discharge pressure should be 190psi, if everything else is the same as my last test.

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Originally Posted by airefresco

So if the condenser is clean, then more heat is rejected, which would then lower discharge pressure/temperature and increase the dT of the water? I should have had a discharge pressure of more or less 190psi? Is that correct?

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Yes!

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What should I then expect the dT to be (with a clean condenser)?

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Ideally, it should be around 5K but it could be lower if water flow is high.

Thank you again, I think I get it now.

I´ve just spoken to the pool company regarding cleaning the condenser. They say it shouldn´t be necessary as the condenser is just tubes within a tube. Also they say the pool chemicals and filters should keep everything clean. Is this true, or do they not know what they are talking about?

What about water flow? They say it´s more likely to be a water flow problem. I would think that if I had poor water flow then I would still have the high discharge, but the dT would be higher? am I wrong in thinking this?

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Originally Posted by airefresco

I´ve just spoken to the pool company regarding cleaning the condenser. They say it shouldn´t be necessary as the condenser is just tubes within a tube. Also they say the pool chemicals and filters should keep everything clean. Is this true, or do they not know what they are talking about?

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If that is the case, then it is some probability that you have noncondensibles in condenser. You could check that by switching off unit and letting condenser pump running, and watch high pressure. If pressure falls slowly, you have noncondensibles. If falls rapidly, than probably there is no noncondensibles in system.
Also, if you are unsure you could leave system with pump ON until temperatures equilase and then compare pressure with temperature for diference.

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What about water flow? They say it´s more likely to be a water flow problem. I would think that if I had poor water flow then I would still have the high discharge, but the dT would be higher? am I wrong in thinking this?

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No.

Sorry Nike, but do you mean no i´m wrong or no it can´t be water flow?

When you say switch the unit off, then you mean switch off the actual heat pump and leave the circulation for the pool running?

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Originally Posted by airefresco

Sorry Nike, but do you mean no i´m wrong or no it can´t be water flow?

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I mean that you are right and that cannot be water flow.

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When you say switch the unit off, then you mean switch off the actual heat pump and leave the circulation for the pool running?

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Yes!

I have not read the rest of the suggestions but how about the following being the cause.
If the system was low on gas and the low ambient stat phial was in the Evaporator then it would cut in and out on that, As being low on gas would cause icing up.
Having worked on swimming pool heat pumps for 20 years i have never had one with a blocked condenser. Is there a bypass in the pool pipe work to the heat pump and is this open not allowing enough water through the condensor causing it to trip on HP.

Unlikely. It didn´t start tripping out until I added some gas and the ice melted. If memory serves me correct, the phial for the stat is near the top of the evaporator.

I´m actually starting to think along those lines to. It has an automic valve which either sends the water straight through the heat pump or through the solars then to the heat pump. I tried that valve in manual in both positions and it didn´t really make any difference to the pressures. The only time the discharge pressure change was when the valve was set to automatic. When it change over, the discharge pressure increase more or less 10 psi for a couple of seconds, but never tripped. When it was tripping, I had it set in manual, bypassing the solars.

I´m going back with the pool company, and they are going to check everything on the water side, just to rule out anything on that side of things.

I´ll keep you posted on my findings.

This has now become Paul´s Heat Pump thread. :)

Went to look at another one today. I think the 3-way valve is faulty, but would love to hear if someone´s got a better suggestion.

Again, no valve on the discharge side, so can only take the suction pressure. Basically, this one isn´t really doing anything. Ambient was 19ºc pool temp was 20ºc. What I noticed is the suction pressure will drop to around 40psi gradually, then you can hear a gush of gas through the expansion valve and pressure flies up to 60psi. It bounces around for a bit between about 50-60 psi then settles down again for a few seconds then all this happens again. Meanwhile the temperatures on the discharge are all over the place, my thermometer couldn´t keep up.

I suspect the 3-way valve is leaking and a small amount of the discharge gas is getting into the suction line. The expansion valve opens to compensate, then closes again, which is causing the pressures to fly around, then gets another blast of hot gas, and process repeats.

It tripped a couple of times on HP while I was there, but I was messing with the flow valves on the water side, so that could have been my fault. I am assured that there is definitely good flow there, it has been tested and was actually too much, so they had to reduce it.

System is similar to the last one I worked on. Only safety devices are HP and water flow. It´s an el cheapo chinese thing. 3-way valve for defrost (which it will never do over here), and expansion valve and then of course the compressor, air cooled evap and water cooled condenser.

i was wondering if you had an air lock in the solar if that was reducing the waterflow through the plate exchanger and causing it to overheat and cut out on HP?

The solar´s were off, I was there first thing in the morning and it was pretty cloudy. Like I said, I wouldn´t take it tripping out on HP as anything, as that could have been my fault, playing with the valves. They´re not plate exchangers either, the pool water goes directly through the heat pump.

I think I´ve sorted the second heat pump. I think there is way too much water going through it. I shut the supply water valve almost completely shut and everything seemed to be working much better. When I looked at the water side of things, the pump is miles too big for the pool. I think there was too much flow before, and no HP trips either. It´s on test over the weekend. So I will see on Monday.

I think I might check the water flow out on the first heat pump now too, as the pool company said that one had good flow too, I don´t really believe them now.

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Originally Posted by airefresco

I think I´ve sorted the second heat pump. I think there is way too much water going through it. I shut the supply water valve almost completely shut and everything seemed to be working much better. When I looked at the water side of things, the pump is miles too big for the pool. I think there was too much flow before, and no HP trips either. It´s on test over the weekend. So I will see on Monday.

I think I might check the water flow out on the first heat pump now too, as the pool company said that one had good flow too, I don´t really believe them now.

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This is probably your scenario:
To much water flow makes heat exchanger with high water pressure drop. Since swimming pool is open system pressure of water at pump inlet is low. If we have high pressure drop at heat exchanger it is possible cavitation inside of heat exchanger and therefore low heat transfer in exchanger. That is why you before having high condensation pressure.
Now, with reduced flow, exchanger is no longer such a high restriction and water pressure drop at him is no longer high and there is no cavitation.

I would like to see opinions of other members about this scenario likelihood.

The best thing for the chinese cheapo Heat Pump is to scrap it and sell them something that might work and last for more than a few years. I hate these things they are nothing but trouble in this country. Nylon nuts on the refrigerant pipe connections, dodgy defrost valves, poor quality parts, no spares readily available, the list is endless.

I know what you mean and I agree. However, I am doing the service work for a pool company that sells them, so i can´t really comment on them to the clients. The thing I hate the most about them is there is no service valve on the discharge side, so you can´t see the discharge pressure. Also the pool company have loads of spare parts (expansion valves, PCB´s, etc) so that´s not really a problem for me.

I´ve repaired 6 heat pumps this week. All were Chinese ones expect for 1 Calorex. 5 had leaks on them and 4 of them were under 2 years old.

Nike - to be honest, I think the second heat pump must have been way over condensing, an I bet if could of taken the discharge pressure, it would have been quite low. I think the gauges bouncing is due to liquid boiling off in the accumulator. The HP trips were probably my fault, it´s ran 24 hours no problem, so far.

Having said that, the first heat pump could be as you described or it could be the opposite and have low flow (more likely low flow).

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Originally Posted by airefresco

Nike - to be honest, I think the second heat pump must have been way over condensing, an I bet if could of taken the discharge pressure, it would have been quite low. I think the gauges bouncing is due to liquid boiling off in the accumulator. The HP trips were probably my fault, it´s ran 24 hours no problem, so far.

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I did not read carefully and I was thinking that you are describing first heat pump in your last post.:o

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Having said that, the first heat pump could be as you described or it could be the opposite and have low flow (more likely low flow).

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If that is the case you will be experiencing high dT of water and you have only 0,8K.

That´s what I thought too. But, I´m quickly learning not to trust every reading i´m getting and double check everything. I really don´t know what to do with the first one. I think I need to go back to basics and recheck everything for myself and not assume anything. Water flows being the first thing to check.

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Originally Posted by airefresco

That´s what I thought too. But, I´m quickly learning not to trust every reading i´m getting and double check everything. I really don´t know what to do with the first one. I think I need to go back to basics and recheck everything for myself and not assume anything. Water flows being the first thing to check.

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Yep, that is the right way.
Make table of required readings and observe some time and note more than one time all readings. That will give you a clearer picture.

First heat pump fixed too. :)

There was air in the water system (a lot of air). There are no bleeding valves on water system, so I´m recommending fitting these to the solar panels (highest point).

I replaced the line-tap valve too while I was there, with a proper brazed one.

So, both these heat pump problems were nothing to do the heat pumps and all down to pool water connections, which on both occasions I was told were good. Still, I learned a thing or too, so not a complete waste of time.

Thanks to everybody who contributed to this thread.

Next time if the unit trips out, try to work out which safety device it has tripped out on by measuring the voltage through each device (if you have time to before it resets)

That way you know if you should be looking at the water side of things or the refrigeration side.
Then again if it trips out on HP it may be due to lack of water flow :o but its always a good thing to start with.

That´s exactly what I was trying to do, but it was too quick for me.

These heat pumps are getting annoying now. Went to another one today. Identical system to the one I had problems with before (post #16), with the exact same problem. This time it´s not caused by water flow. Reducing the water flow on this system made very little difference. There used to another heat pump that worked fine and the pool maintained 30ºc all year round. This system replaced that heat pump. I went through the full water system with the pool company and everything seems to be correct, including the solars.

What I think I need to find out is why the suction pressure fluctuates so much. I assume this is an indication of liquid boiling off in the suction line and/or accumulator ( the service valve is just before the accumulator).

Without being able to see the high side pressures it´s difficult to diagnose, but I think it must be either something to do the system over condensing or something on the TXV. Am I correct in thinking this? The system is being replaced tomorrow and will be taken to the pool companies workshop, where I can experiment a little.

Some thermodynamics based on your OP:

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T,sat
1. R-22 51.22 Saturated Vapor
2. R-22 -0.2032 Saturated Vapor
3. R-22 -0.2032 Saturated Liquid

Condenser:
Tg,in = 77.3'C
T,sat = 51.22'C
T,liq = 23.8'C

De-superheating = 77.3 - 51.22 = 26.08'C (reasonable)
Subcooling = 51.22 - 23.8 = 27.42'C !!! (liquid too cold in my view)

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Looks like either a gas leak, or a restriction in the liquid line.

Thanks, but that system seems to be ok since getting the air out of the water system. I hope I am not jinxing it now.

^ If your original readings were correct - the thermodynamics don't lie... :)

Consider a liquid line blockage at your next call-out, or low gas charge. Perhaps there is some icing of the TXV?