Home made swimming pool heat pump

[Acuario]

Hi all,
I would like to convert an old a/c unit I have into a heat pump for my swimming pool. I have an external fujitsu AOG25AWNL unit (I can find no information about it anywhere). The unit is R22 and has a Tecumseh AW5532A compressor (reciprocating I think), again little/no information although in the Tecomseh equivalents it seems close to a AWA5532EXV (is it??), around 31/32 KBTUh.

So, the idea is:
The condenser is in the unit; cut the pipes and 're plumb' the pipework to take direct from the compressor out through a 3 port valve and to an external heat exchanger (the new condenser) , back via another 3 port valve and through the capillary and into the condenser (which now has becomes the evaporator) and from the 'new' evaporator back to the compressor. The condenser appears to have two circuits through it that are linked at either end. The liquid end I plan to leave but the gas end I plan to cut and braise to feed the two tubes into a 1/2" tube to connect back to the gas side of the compressor.

The heat exchanger will be interesting. I'm planning to build it from a piece of 90mm soil pipe, 50mm connections on either end for the pool water and with a wound coil inside to take the refrigerant. I have no idea how long this will need to be so as I have limited space I'm just going to size it to fit the space which is about 90cm.

So, does anyone see any glaring errors in my plan? I haven't started yet so am open to suggestions. Also does anyone have any information on the external unit I have.

Thanks,

Nigel

[frank]

The chlorine in the pool water will eat through the copper refrigeration pipe coil in no time leading to a loss of refrigerant, compressor and associated components.

It's a non starter for an amateur

[Acuario]

I've been pumping chlorinated water from my pool through copper pipes on my solar hot water panels for years with no ill effects - it depends on the ph of the water which I keep within the recommended range so I'm not concerned about possible corrosion problems.

[monkey spanners]

What Frank said, may be a good idea to source an condenser from a swiming pool heat pump manufacturer.

You will need to replace the capillary tube with a txv, fit a reciever or reciever drier, an anti cycle timer for the comp, a flow switch, lp and hp switches, a thermostat/thermometer, defrost stat and hot gas bypass valve.

Jon

[Brian_UK]

We might also add that as a 'new build' it will be illegal to use R22.

[Acuario]

What Frank said, may be a good idea to source an condenser from a swiming pool heat pump manufacturer.

You will need to replace the capillary tube with a txv, fit a reciever or reciever drier, an anti cycle timer for the comp, a flow switch, lp and hp switches, a thermostat/thermometer, defrost stat and hot gas bypass valve.

Jon

Ok, thanks for the reply. One thing though, why so complex? What do all these bits 'add' or do? Surely as I have what is a functioning split a/c unit with a condensor and evaporator I can swap the heat exchangers so I use the heating effect rather than the cooling - I'm not trying to build a dual function device. Ok, I'm changing the design of one bit as I want water to refrigerant rather than air to refrigerant heat transfer but why so complex? What would happen without the extra bits? Would it work/not work/blow up?

Nigel

[monkey spanners]

Ok, thanks for the reply. One thing though, why so complex? What do all these bits 'add' or do? Surely as I have what is a functioning split a/c unit with a condensor and evaporator I can swap the heat exchangers so I use the heating effect rather than the cooling - I'm not trying to build a dual function device. Ok, I'm changing the design of one bit as I want water to refrigerant rather than air to refrigerant heat transfer but why so complex? What would happen without the extra bits? Would it work/not work/blow up?

Nigel

The flow switch will prevent the system running when there is no water flow in the condenser. This would be bad.
The lp and hp switches will turn the system off in the event of high or low pressure fault condidtions. This could be equally bad, people have been killed due to none working pressure switches.
The delay timer when suitably programed will prevent the compressor starting before the system pressures have had a chance to equalise, as your compressor will likely be a low starting torque version. (a hard start kit may be a worthwhile adition too)
The txv will better modulate refrigerant flow now that you will have a low head pressure (dictated by water temperature) and a variable evaporator load depending on air temp and frost accumilation. (a balanced port txv would be the best buy)
The frost stat together with the hot gas bypass valve will initiate and terminate a defrost cycle on the evaporator to keep it clear of excessive frost.
Reciever/reciever drier will provide a buffer for the excess refrigerant as the txv modulates.
Thermostat to turn it off and on as water temperature dictates.

So some of the 'complications' make the system safer for you and itself, and others make it more efficient.

You will also need an f gas certificate if you are in europe as its now illeagal to work on refrigerating systems without one, and as Brian pointed out R22 is now longer allowed in new systems, so a drop in replacement will be needed.


Jon

[McFranklin]

What are you trying to accomplish? Are you trying to heat your pool water or cool your house or both? When I read the post I interpeted it that you were just trying to heat your pool water.Is that correct?

If you are, why not just purchase and install an electric heater?
If you are using heat that would otherwise be rejected to the atmosphere I could understand this going through all of this trouble.

Unless you are setting up an air conditioning system to remove heat from some other area, and are using the swimming pool as a heatsink, all you have is an overly complicated electric heater.

And if I were running the air conditioner to cool the house, I don't think I would want to make my swimming pool warmer. Of course, I have never had a pool so there may be something I am missing.

[Acuario]

The idea is only to heat the pool. The reason I opted for an a/c unit is basically efficiency - the compressor in the unit has a COP of 3.02, ok, I probably won't get that in reality but nonetheless I will hopefully get more heat out than energy in. Also I like to recycle stuff. The whole unit cost me 30 euros, I'm estimating bits will be around 60 euros so for the whole system it will have cost me 90 euros, a far cry from the 1800 euros for a commercial machine.

Also it's a fun project. Anyone can go buy an X and fit it but do you learn anything from doing it? This is an interesting project just from some of the challenges, learning a bit about refrigeration, heat exchangers, control systems etc.. better than sitting in watching TV :-) The advice and knowledge from Jon is excellent, what or how much I'll try is still to be seen but certainly there are a few points I hadn't thought about, thanks Jon!

I live in Spain, have a pool with cover and already heat it with solar panels however I would like to extend the swimming season. I have already additionally tried with a gas water heater modified to stack 2 heat exchangers one above the other (works well!), also I have an old steel indirect heated domestic hot water cylinder that I have coupled up to the pool, I burn my garden waste inside and that generates loads of heat, this works well too, so I thought 'Why not try with an old air conditioner', hence this project.

I install air conditioners already so I have all the equipment for making up the pipework, brazing, filling guages, gas etc. so I dont need to invest in special tools. Also, as an electronics engineer I can fairly easily put together any control system that may be necessary including designing any processor/software that may be needed.

Nigel

[desA]

You look to be all set then. All the best.

[Acuario]

The flow switch will prevent the system running when there is no water flow in the condenser. This would be bad.
The lp and hp switches will turn the system off in the event of high or low pressure fault condidtions. This could be equally bad, people have been killed due to none working pressure switches.
The delay timer when suitably programed will prevent the compressor starting before the system pressures have had a chance to equalise, as your compressor will likely be a low starting torque version. (a hard start kit may be a worthwhile adition too)
The txv will better modulate refrigerant flow now that you will have a low head pressure (dictated by water temperature) and a variable evaporator load depending on air temp and frost accumilation. (a balanced port txv would be the best buy)
The frost stat together with the hot gas bypass valve will initiate and terminate a defrost cycle on the evaporator to keep it clear of excessive frost.
Reciever/reciever drier will provide a buffer for the excess refrigerant as the txv modulates.
Thermostat to turn it off and on as water temperature dictates.

So some of the 'complications' make the system safer for you and itself, and others make it more efficient.

You will also need an f gas certificate if you are in europe as its now illeagal to work on refrigerating systems without one, and as Brian pointed out R22 is now longer allowed in new systems, so a drop in replacement will be needed.


Jon

Excellent information, thanks. Re the high/low pressure switches, what pressures would you expect to see. I assume these switches are at preset pressures. From what I have read refrigerant pressure is related to differential in temperature so a 'working pressure' is impossible to determine unless the temperatures are known. So, I would assume that the switch would operate in case of excess pressure, but what pressure is classed as excess pressure and, as it is not a DC compressor how can the pressure be regulated?

Interestingly, studying the circuit of the unit that this 'split' came from the outdoor unit is very simple - it is simply switched on and off by the control board and has no feedback of information to the control board or any apparent safety features. It has an outdoor thermostat to control the fan and that's about it.

The internal unit has a pipe temperature and room temperature thermistor and that's it. There are no pressure sensors anywhere. Is this normal on older machines, this machine seems to be from around the mid 90's.

Re the system pressures equalising, surely in a non operating state there are no pressure differentials throughout the system and everything is in equilibrium, starting the compressor generates that differential and refrigerant starts to circulate or am I missing something?

Thanks for the information,

Nigel

[monkey spanners]

The low pressure switch would be set to turn the system off in a low load condition, or if there was a leak, either case can damage the compressor after a time.
Excessivly high pressures are prevented during normal operation by propper sizing of the various components to match the cooling/heating duty, and during fault conditions by the pressure switches.
The high pressure switch would be set to turn the system off before the maximum safe pressure of the condenser/compressor or other components is reached.
The system may take anywhere from a few minutes to hours depending on various things to equalise, or there may be a power cut for a few seconds or a customer adjusting the thermostat, or pool pump so a delay timer is good insurance against a burnt out compressor.

Many air con systems use pipe temperature sensors and circuit boards to provide low and high pressure protection (and delay start timer), but some older and cheaper stuff will just run till something blows up/burns out....

Jon

[Gary]

So, I would assume that the switch would operate in case of excess pressure, but what pressure is classed as excess pressure and, as it is not a DC compressor how can the pressure be regulated?

Refrigeration is not about pressures, it is about heat transfer. If the rate of heat transfer is right across each transfer point, then the pressures and temperatures will be right.

You might want to start here:

http://www.refrigeration-engineer.co...ad.php?t=19701

[Magoo]

Solar panels would be more effective and cheaper

[DrFreezeMD]

The unit that is mentioned is about 36,000 BTUH. Sounds too small to me. The Heat pump Pool units I have seen have been 60,000 BTUH to 90,000 BTUH. Then again I do know the size of your pool and how quickly you want the water to reach your set point. And some of the advice you have received from other members is good.

[Acuario]

Solar panels would be more effective and cheaper

I already have solar panels connected via a central heating circulating pump. Very effective, the pool gets up to 36C+ in the summer so I have to run the panels at night to cool the water. Unfortunately not so good in the winter months as there still is sun but not so many hours or solar radiation.

[desA]

Refrigeration is not about pressures, it is about heat transfer. If the rate of heat transfer is right across each transfer point, then the pressures and temperatures will be right.

Perfect.

[Acuario]

To follow up, and so the forum doesn't have yet another thread without closure, I built it, installed it and it works, it hasn't blown up yet either. My pool (50,000 litres approx) heated up from 15 degrees to 22 degrees in about a week, unfortunately since we've had some really cold weather so the pool losses have been high and I've not been able to heat all the time (see below). It did, however, reach 26 degrees on 21st January and I went swimming.

Yes there are 'problems'. I've woken up to find I have a block of ice a couple of times when it is particularly cold overnight, I'll work on a solution for that but hopefully it'll only happen ocasionally and when it does I just turn it off and it unfreezes. I calculated (very, very roughly!) that I'm getting a COP of around 2.4 so have achieved my objective, now I need to work out how to improve it as it should be higher.

It's been a great learning experience and I'm keen to continue learning, after all that was the objective, super heat, sub cooling, TXV's, pt charts etc, all good stuff, I'm still reading, still absorbing info..... I need to add a couple or three more valves so I can see what pressures I'm getting at various points, that will help my understanding as all I can do at the moment is measure tube temperatures and the pressure at the exit of the compressor.

Nigel

[nevgee]

The chlorine in the pool water will eat through the copper refrigeration pipe coil in no time leading to a loss of refrigerant, compressor and associated components.

I would have agreed with you some years back, but the truth is, there is really no problem at all with Chlorine treatment of pools and copper. However, strangely as it seems, if the pool operator doesn't keep the chlorine level right, ie high enough, then there would be a problem with corrosion. The Chlorine oxidises organic material in the pool, if there is insufficient free Chlorine then Chloramines are produced. It's these Chloramines that give the "chlorine" smell in pools and also causes sore eyes.

Children are a common factor here!

So when you smell chlorine in a pool hall it indicates the treament is off or not being kept up to adequate levels to combat the chidren

[nevgee]

Yes there are 'problems'. I've woken up to find I have a block of ice a couple of times when it is particularly cold overnight, I'll work on a solution for that but hopefully it'll only happen ocasionally and when it does I just turn it off and it unfreezes. I calculated (very, very roughly!) that I'm getting a COP of around 2.4 so have achieved my objective, now I need to work out how to improve it as it should be higher.


Nigel

Fit a defrost controller that activates defrost say every hour and terminates on temperature, say at 15C with a time activated termination after say 10 mins. place the temp probe 1 tube in 1 row up from bottom of evaporator, air off side .

[Acuario]

My idea is along these lines. I'm thinking of fitting a frost stat on the case somewhere and shutting off the compressor when it gets too cold and then a delay timer to start it up again when the temperature rises. this way I have both the hysterisis of the thermostat and a time delay to make sure. I'm thinking of incorporating the delay into the startup as well to cater for any short power outages that we have (in Spain the power is a bit interesting sometimes!).

Nigel

[Gary]

It's been a great learning experience and I'm keen to continue learning, after all that was the objective, super heat, sub cooling, TXV's, pt charts etc, all good stuff, I'm still reading, still absorbing info..... I need to add a couple or three more valves so I can see what pressures I'm getting at various points, that will help my understanding as all I can do at the moment is measure tube temperatures and the pressure at the exit of the compressor.

Nigel

It will be interesting to see all of the pressures and temperatures, so we can help you fine tune the system.

[install monkey]

hows ur electric bill? has ur converted fujitsu system got an rcd fitted and is it well earthed? did u know theres an additive thas oil based to give a thin film on top of the pool to reduce heat loss! may help in running costs

[desA]

I'd love to know the compressor discharge temperature.

[Acuario]

Gary; what temperatures would you like to know? Pressures are more difficult at the moment however today (8C air temp) the pressure at the compressor exit was 22 bar. I'd really apreciate any help in tuning it. I also have a load of questions that I'll post later.

Install monkey; I daren't look at the electric meter! Yes I have an RCD connected and it's well earthed. I ran a seperate circuit for it. I've seen the oil film but I already have a full cover and a solar blanket so there's not much more I can do to reduce losses.

desA; today, with air temperature at 8C the discharge temperature (on the pipe) was 73.9C. I have seen it higher when the air temperature was higher; up in the 85-90 degree range.

I have put together a web page with pictures on my website if anyone is interested in seeing what I did. I need 15 posts before I can add it though so I'll post some of my questions first.

Nigel

[Acuario]

Question;
How much refrigerant do I need? The unit as new was charged with 1950g and was designed to connect to an internal unit that had quite a large heat exchanger. I had to recover the gas before doing the mods but how much should I refill it as my heat exchanger is a) much closer and b)much smaller than the original. At the moment I'm running with a charge of around 1Kg.

[Acuario]

Another question;
Having read about super heat and looked at the R22 P-T chart am I correct in thinking that in my case with the pressure at (roughly) 322psig the boiling point is 57C so with a pipe temperature of 73.9C I have a superheat of 16.9C? Is this what I should expect or is something horribly wrong?

[Acuario]

How do you tell at any point in a refrigeration circuit if the refrigerant is in a liquid or gas form? When the refrigerant leaves the compressor it is liquid. From everything I've read, when it leaves the capillary or TXV it should be in a gas form, or at least the majority of it should be, the remainder should boil off en-route through the evaporator but how can you tell if this is what has happened? Is it only by direct temperature/pressure measurement?

[Acuario]

I was talking to my parts/gas supplier a couple of days ago about replacements for R22. From what I had read to date the recommended drop in replacement for R22 is R422D but this means recovering the R22 and replacing the charge. My supplier told me they now supply RS44 and that you can mix the two so no need to recover the R22. Anyone had any experience of this?

[Acuario]

Copper in chlorinated water. I've put a spare bit of tube in the filter basket on my pool pump which has to be one of the most volatile places for a tube to be as it has no chance of forming an oxide layer to protect itself from corrosion. So far no change, no degredation, it hasn't even lost its dullness which would be a sure sign of corrosion. I'm going to keep it in there just in case!

[Acuario]

Sorry for this pointless post to get my 15 but I can't think of another question at the moment :-(

[Acuario]

Ok, hopefully now I can post the link to the pictures.

http://www.costadoradaholiday.com/poolheater.html

[desA]

Gary; what temperatures would you like to know? Pressures are more difficult at the moment however today (8C air temp) the pressure at the compressor exit was 22 bar. I'd really apreciate any help in tuning it. I also have a load of questions that I'll post later.

Install monkey; I daren't look at the electric meter! Yes I have an RCD connected and it's well earthed. I ran a seperate circuit for it. I've seen the oil film but I already have a full cover and a solar blanket so there's not much more I can do to reduce losses.

desA; today, with air temperature at 8C the discharge temperature (on the pipe) was 73.9C. I have seen it higher when the air temperature was higher; up in the 85-90 degree range.

I have put together a web page with pictures on my website if anyone is interested in seeing what I did. I need 15 posts before I can add it though so I'll post some of my questions first.

Nigel

If you are using R22 at Tc,sat~51.75'C , Te,sat~3'C , I'd predict a compressor discharge temp ~ 104.9'C at compressor discharge. Measured 150mm from compressor, it will be a tad lower, but not 73.9'C.

For Tc,sat~51.75'C , Te,sat~0'C, Tdisch ~ 108.7'C

Struggling to read your LP temp readings.

You may want to re-check this, & in view of mineral oil breakdown.

[Acuario]

I just re checked (my temperature probe isn't really too good at testing spot temperatures) and got a reading of 82'C. This is at the valve which is something like 500mm from the compressor. Is this better? I'm still not sure how accurate it is though.
Can you tell me what Tc,sat and Te,sat are?

If you looked at the picture of the guages only the HP side is connected as I only have 1 valve at the moment.

Nigel

[desA]

If you are using R22 at Tc,sat~51.75'C , Te,sat~3'C , I'd predict a compressor discharge temp ~ 104.9'C at compressor discharge. Measured 150mm from compressor, it will be a tad lower, but not 73.9'C.

For Tc,sat~51.75'C , Te,sat~0'C, Tdisch ~ 108.7'C

Struggling to read your LP temp readings.

You may want to re-check this, & in view of mineral oil breakdown.

Ok, making a little more sense from your website. Really do need a reading on the LP gauge.

For Tc,sat~57.75'C , Te,sat~-35'C (surely not?), Tdisch ~ 174.3'C

[desA]

I just re checked (my temperature probe isn't really too good at testing spot temperatures) and got a reading of 82'C. This is at the valve which is something like 500mm from the compressor. Is this better? I'm still not sure how accurate it is though.
Can you tell me what Tc,sat and Te,sat are?

If you looked at the picture of the guages only the HP side is connected as I only have 1 valve at the moment.

Nigel

Testing standard is 150mm from compressor discharge. Bare pipe, sand-paper, strap sensor to pipe surface, insulate, take measurement.

[desA]

Please take a more clear picture of your LP/HP gauge faces & post these.

[install monkey]

when the pool reaches setpoint have u got a thermostat to stop the condenser?u would need a differential of about 3 deg to prevent short cycling between startups also to allow the pressures to equalise. this would aid in defrosting ur evap coil.

[Acuario]

Please take a more clear picture of your LP/HP gauge faces & post these.

here it is.
http://www.costadoradaholiday.com/guages.jpg

[Acuario]

when the pool reaches setpoint have u got a thermostat to stop the condenser?u would need a differential of about 3 deg to prevent short cycling between startups also to allow the pressures to equalise. this would aid in defrosting ur evap coil.

No, nothing yet - maybe later! I like my pool warm. It'll probably be a manual process at the moment but the pool is such a huge heat sink that any rapid fluctuations in temperature are impossible. I've not yet seen an increase of more than 2.5'C in 24 hours.

[desA]

here it is.
http://www.costadoradaholiday.com/guages.jpg

Excellent. The LP is showing Te,sat=-35'C. Is this so?

If that is really so, then Tdisch~174.3'C. & something is really not happy. Your compressor will fall over if things carry on like this.

You'll need to give us a lot more information. Take a look at Gary's excellent thread http://www.refrigeration-engineer.co...ad.php?t=19701 for the correct information to give us. I'm sure someone will be able to assist.

[MikeHolm]

From just a quick look that seems like an really small condenser coil HX. Des, what do you think?

[Acuario]

The LP side isn't connected to anything as I don't have any valve to connect to - it's something I need to do at some point. I currently only have one valve on the HP side where the pipe exits the unit and goes to the feed pipe to the heat exchanger.

[desA]

From just a quick look that seems like an really small condenser coil HX. Des, what do you think?

Way too small.

My first impression is that the system is radically under-charge, hence Te,sat~-35'C. As refrigerant is added, the tiny condenser coil will not transfer enough heat & the high-side pressure will rise dramatically. The cap tube dimensions will probably be all wrong for this new system balance (will see as project progresses).

[MikeHolm]

For solar heating with plastic panels (min 50% pool surface area in collector area) we look at a typical dT across the panels of 4-5c. We expect the pool to increase in temp at about 4-5C daily from 7-10C fill temp to an average 28C final temp and it doesn't take a lot of heating to keep it there if the pool blanket is used and there is not much wind or shading on the panels. Obviously this is the case with this pool.
I would think that there would need to be at least 3 parallel windings (with different diameters, 50mm, 75mm,100mm) in a larger pipe to get a better transfer.

On a related note regarding pools and ph, we used to install zinc pucks with holes in them in the discharge to the pool and as the zinc is a natural algaecide and fungicide, the need for chlorine was reduced by 80%. The CSA and UL committees in North America are led by members of the pool service and manufacturers so they would not allow these alternatives to be instituted here. The system worked really well and lasted 15 years (so far) but it took away a lot of the industries revenue so we are stuck with either chlorine or salt water pools.

[Acuario]

I have about 25% pool surface at the moment, it heats well in sunshine and gets up to 36'C in the summer - I sometimes have to run them overnight to dump heat.

It looks like I need to start planning Heat Exchanger Mk II but Mk I is working well. The pool pump pumps 20,500 litres per hour and I'm getting a dT of nearly 40'C across it in the refrigerant line. It can't go too low on the exit (currently around 38'C) or I'll be heating the refrigerant with the pool.

Interesting about the zinc. What is the general application of the pucks you used, are they generally available? Where exactly did you fit them in the hydraulic circuit?

[desA]

I fear that you may very well burn out your compressor before too long.

[MikeHolm]

Firstly you need a much higher pool flow across the heat exchanger. If you are using a comma in the normal European way (20.4l/h in north american) than this is way too slow. You should have at least 15000L/h through the pool filter which needs 50mm piping. Des can speak to the compressor performance MUCH better than I.

I don't know if the pool panels are plastic or copper but per m2 it is not much different. The plastic panel is better in some ways as it also will take heat from a black roof where it may be located and is better in incident angles....where the sun is not perpendicular to the face of the panel but the glazed copper one will give much better performance when the ambient temp is lower.

I have tried to find the zinc pucks from the manufacturer but all reference to them has disappeared. It is quite a simple device, a series of zinc discs 75mm diameter and 25mm thick with a number of holes formed in them are placed in a PVC pipe after the pool filter. It is a sacrificial unit but takes a lot of time to degrade. It slowly introduces the molecular zinc which will not leave the water although some of it will get caught in the filter but in general it is highly diffused. it is in skin creams, dandruff shampoo etc. and is considered quite safe.

[Acuario]

Firstly you need a much higher pool flow across the heat exchanger. If you are using a comma in the normal European way (20.4l/h in north american) than this is way too slow. You should have at least 15000L/h through the pool filter which needs 50mm piping. Des can speak to the compressor performance MUCH better than I.

I don't know if the pool panels are plastic or copper but per m2 it is not much different. The plastic panel is better in some ways as it also will take heat from a black roof where it may be located and is better in incident angles....where the sun is not perpendicular to the face of the panel but the glazed copper one will give much better performance when the ambient temp is lower.

I have tried to find the zinc pucks from the manufacturer but all reference to them has disappeared. It is quite a simple device, a series of zinc discs 75mm diameter and 25mm thick with a number of holes formed in them are placed in a PVC pipe after the pool filter. It is a sacrificial unit but takes a lot of time to degrade. It slowly introduces the molecular zinc which will not leave the water although some of it will get caught in the filter but in general it is highly diffused. it is in skin creams, dandruff shampoo etc. and is considered quite safe.

The frow rate is 20500L/h through the pump/filter, pipework to/from pool sump/skimmers/jets is 50mm, heat exchanger is in a 90mm section.

Des, the guage reading on the LP side is irrelevant as the guage is not connected to anything as I have no valve to connect it to to take a reading - I plan to put one in but haven't yet. Only valid pressure reading is the HP one at 22 bar.

Zinc washer pool sanitiser, now there's a thoughy

[Gary]

Low side:

Evap air in temp
Evap air out temp
Saturated suction temp (SST) aka Te,sat aka low side boiling point
Suction line temp near evap exit
Suction line temp near compressor inlet

High side:

Cond water in temp
Cond water out temp
Saturated condensing temp (SCT) aka Tc,sat aka high side boiling point
Liquid line temp near receiver outlet
Liquid line temp near TXV inlet