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? :confused:

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? :confused:

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.com/forums/showthread.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! :eek:

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 :eek:

[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.com/forums/showthread.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 :D

[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

[desA]

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.

LOL - may want to re-calibrate your gauge, mind.

Then, with all due respect, we are unable to assist further, until you collect the data listed by Gary above. :)

[Gary]

Boiling point, while being a term familiar to the general public, is not commonly used in the refrigeration industry. We generally refer to the P/T conversion as saturation.

If you look at your gauges, you will see a scale that is identified as R22. This gives you the same information as the P/T chart (saturation temp) and is far more convenient.

[Gary]

For a starting point, we need the air and water temps as these have an enormous effect on everything else, but a full set of readings is needed for a full evaluation.

[frank]

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! :eek:

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 :eek:
Some years back, a friend asked me to have alook at his fathers pool heater.

A basic set up with a condensing unit, maybe 1hp, situated within his large green house and a stainless steel cylinder with copper discharge pipework coil running through it. It looked like a home made jobby.

When I connected my gauges on the suction rotolock, water came out :eek:

When It was stripped in our workshop, the discharge copper coil was disintegrating,

I managed to replace it, dry out the existing condenser, rebuild it and re-install it back into his greenhouse. It's still going strong :D

I used 316 S/S tubing though, not copper in the re-build.

I haven't worked on any S & T HX's for pools since, only brazed plate HX's

[Gary]

The best way to calibrate your gauge is to attach it to your R22 container, along with a temp sensor taped to the side of the container. The R22 (saturation temp) scale on the gauge should match the temp of the container.

[Gary]

Some years back, a friend asked me to have alook at his fathers pool heater.

A basic set up with a condensing unit, maybe 1hp, situated within his large green house and a stainless steel cylinder with copper discharge pipework coil running through it. It looked like a home made jobby.

When I connected my gauges on the suction rotolock, water came out :eek:

When It was stripped in our workshop, the discharge copper coil was disintegrating,

I managed to replace it, dry out the existing condenser, rebuild it and re-install it back into his greenhouse. It's still going strong :D

I used 316 S/S tubing though, not copper in the re-build.

I haven't worked on any S & T HX's for pools since, only brazed plate HX's

I'm wondering if the corrosion might have been the result of using dissimilar metals.

[Acuario]

Excellent information and so simple!
I'll take readings as soon as I can but I'm going to need to get and fit a valve on the LP side first. I don't have one so it may be a few days.

Thanks all for the information to date. The pool has heated up about 1'C in the last 10 hours so something is working half right at least!

[Acuario]

I'm wondering if the corrosion might have been the result of using dissimilar metals.

Sounds like it to me - according to nobility table stainless steel is quite anodic and far away from copper which is cathodic with the result being that the copper will corrode.

[frank]

I'm wondering if the corrosion might have been the result of using dissimilar metals.

The corrosion was not at the point where the copper entered the s/s cylinder. It was the majority of the coil within the cylinder which was in constant contact with the circulating chlorine water.

[Acuario]

I've seen this happen with copper cold water pipes that were connected to galvanized iron fittings. I went into a customers garage and there was a fine mist of water being sprayed from the numetous micro perforations in the pipe. How it hadn't burst I'll never know. The whole length was pretty much the same. Water conducts electricity.

Also, years ago my dad worked for the gas company in the UK. In the late 60's/early 70's there was a shortage of copper pipe so they decided to install central heating with steel pipe. Total disaster, it all had to be ripped out and replaced due to electrolysis destroying the steel pipe.

[Gary]

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.

The dT is the water out temp minus the water in temp. So... if the dT is 40C and the water out is 38C, then the water in is -2C? Somehow I doubt this. :)

[Acuario]

Sorry, you mis understood. The temperature of the refrigerant line into the exchanger is around 76'C, the exit temperature of the refrigerant line is 38'C so the temp drop across the exchanger in the refrigerant line is nearly 40'C, in terms of water temperature I doubt it's much, maybe 1 or 2 degrees but I haven't measured it. I'm sure there's some equation somewhere that would say what it was. At the end of the day there is heat transfer, that is what is important.

[Gary]

If the refrigerant leaving temp is 38C and the SCT is 57.5C, then the SC is 57.5-38=19.5K. This indicates liquid is backing up into the condenser, reducing heat transfer. The system is overcharged. The SC should 5.5-8.5K.

The change in refrigerant temperature between the inlet and outlet tells us nothing about heat transfer, because there is a change of state from vapor to liquid. A change of state involves heat transfer without temperature change.

[frank]

If the water in/water out temp difference is only 1C then you need to slow the water flow down.

This will increase the dwell time and allow a greater heat transfer, which will result in a lower discharge pressure

Throttle the valve before/after the pump and let us know what the results are

[monkey spanners]

Head pressure seems very high.....
Wonder if the cap tube is too restrictive?
You really want a txv in this sort of application, preferably one with a balanced port design.

Something to think about is what you want is a high energy transfer from the refrigerant to the water, which is not necessarily best made by a high refrigerant temperature.

[Gary]

First remove refrigerant until the SC is no more than 8.5K, then try adjusting the water flow.

When reducing water flow, if the SCT (discharge pressure) drops, that indicates increased heat transfer. If the SCT rises, you have gone too far and the water flow is insufficient. Whatever flow gives you the lowest SCT.

[Gary]

Head pressure seems very high.....
Wonder if the cap tube is too restrictive?
You really want a txv in this sort of application, preferably one with a balanced port design.

Something to think about is what you want is a high energy transfer from the refrigerant to the water, which is not necessarily best made by a high refrigerant temperature.

I would suspect that the pressure is high because the condenser is woefully inadequate, but at this point we don't have enough information to make the call.

[Gary]

In the condenser, I assume the refrigerant and the water flow in opposite directions (counterflow). If this is not the case, it will need to be re-piped.

[Acuario]

Wow, what a change! Looks like it was seriously over charged. I removed a load (sorry for the technical term) of refrigerant and now it's running with a head pressure of 15bar. I did calibrate my guages first.:)

The changes were dramatic. Previously there was frost/ice forming between the end of the evaporator and all down the compressor suction pipe. Now there is frost after the capillary and on the botttom rows of the evaporator coils. The temperatures have also changed dramatically. They are as follow:

Exit from compressor (measured at 150mm) 106'C, entry to the heat exchanger 84'C, exit of heat exchanger 28.8'C, exit from capillary (entry to evaporator) -13.8'C, exit from evaporator 6.8'C. All measurements taken with the case off which I'm sure makes a difference. Pressure at the one point I can measure, 15bar.

I tried reducing the water flow but as I don't have a bypass valve my poor pool pump started complaining so I don't think this is an option at the moment.

Just to confirm, the heat exchanger is configured to counter flow water against refrigerant.

[desA]

If we assume some further flashing after cap tube (typically is an additional 2-3K)

Te,sat~-16.8'C ; Tc,sat~55.6'C ;
SH=6.8-(-16.8)= 23.6K
SC=55.6-28.8=26.8K
Tdisch~160.3'C

You'll really need to get the LP side connected & sort out decent temp measurement info.

A few thoughts:
If your data is at all believable, it shows to me that you may be between a rock & a hard place in terms of excessive SH & SC. Adding charge may assist SH, but will bother SC - removing charge will have the opposite effect. If your info turns out to be close, then you'll probably want to also look at your cap tube design, 'evap' pipework & fan speed, condenser... a little more.

You must be having fun... :D

[Gary]

If we assume some further flashing after cap tube (typically is an additional 2-3K)

Te,sat~-16.8'C ; Tc,sat~55.6'C ;
SH=6.8-(-16.8)= 23.6K
SC=55.6-28.8=26.8K
Tdisch~160.3'C


Wouldn't 15 bar make Tc,sat ~41'C?

[Gary]

Wow, what a change! Looks like it was seriously over charged. I removed a load (sorry for the technical term) of refrigerant and now it's running with a head pressure of 15bar. I did calibrate my guages first.:)

The changes were dramatic. Previously there was frost/ice forming between the end of the evaporator and all down the compressor suction pipe. Now there is frost after the capillary and on the botttom rows of the evaporator coils. The temperatures have also changed dramatically. They are as follow:

Exit from compressor (measured at 150mm) 106'C, entry to the heat exchanger 84'C, exit of heat exchanger 28.8'C, exit from capillary (entry to evaporator) -13.8'C, exit from evaporator 6.8'C. All measurements taken with the case off which I'm sure makes a difference. Pressure at the one point I can measure, 15bar.

I tried reducing the water flow but as I don't have a bypass valve my poor pool pump started complaining so I don't think this is an option at the moment.

Just to confirm, the heat exchanger is configured to counter flow water against refrigerant.

Ambient temp? Pool water temp?

[desA]

Wouldn't 15 bar make Tc,sat ~41'C?

Quite correct ~ 41.78'C. Finger trouble - had yesterday's results stuck in me noggin. :confused:

Te,sat~-16.8'C ; Tc,sat~41.78'C ;
SH=6.8-(-16.8)= 23.6K
SC=41.78-28.8=12.98K
Tdisch~135.6'C

[Gary]

A few thoughts:
If your data is at all believable, it shows to me that you may be between a rock & a hard place in terms of excessive SH & SC. Adding charge may assist SH, but will bother SC - removing charge will have the opposite effect. If your info turns out to be close, then you'll probably want to also look at your cap tube design, 'evap' pipework & fan speed, condenser... a little more.


A rock & a hard place indeed. We may be able to compensate with fan speed for current conditions, but it all changes with warm weather. This system would be MUCH better off with a TXV.

[Gary]

You indicated in an earlier post that the fan was set to full speed. This implies that it's speed can be adjusted.

I would slow the fan until the entire coil is evenly frosted and the suction line is partially frosted, the frost ending before it reaches the compressor inlet.

[Gary]

On any condensing unit, the condenser is sized to handle both the heat of evaporation and the heat of compression. Since we are now using it as the evaporator, we can assume that it's capacity is such that it is capable of overwhelming and overloading the compressor. The capacity needs to be reduced by reducing the airflow through it, in order to properly match the compressor... or it will destroy the compressor in warm weather.

[Gary]

I am assuming this cap tube is also from the original system. This being the case, it is sized to provide proper refrigerant mass flow under warm (A/C) evaporator conditions. This makes it ideal for warm weather operations, but just as an A/C, if run under abnormally cold indoor conditions, in cold ambients it can flood the compressor. We can compensate for this by limiting the refrigerant charge, such that in cold ambients it runs low (but not dangerously low) superheat.

In warm weather, it will then run high superheat, but this is probably the best we can do.

[Acuario]

Des, I'm having great fun, just what I wanted from this project, and learning a lot!

Ambient temp this morning was 7.5'C, pool water temp 22'C. This was when I calibrated my guages so I remember it well!

The fan as standard has 2 speeds, I'll try and build a controller to make it variable. At the moment I'm getting frost/ice buildup on 2/3 of the evaporator; is this a good thing or is it better not to have it frosting up and hence restricting air flow? I've put a mechanical timer on the compressor to turn it off for 15 minutes every hour or so to let it defrost with the fan still running.

I take the point about the TXV, I'll see if my bits supplier has one. Any spec I need to look out for?

The capillary is the original one, as is basically everything. From what you say Gary, should I block some of the evaporator or just reduce the fan speed? I'm not planning to use this when there is hot weather as it doesn't need it. The plan is to just use it in winter and the solar panels in summer with a changeover during spring/autumn.

[Gary]

Try switching the fan to low speed and let's see what the pressure and all of the temperatures then look like.

[Gary]

At the moment I'm getting frost/ice buildup on 2/3 of the evaporator; is this a good thing or is it better not to have it frosting up and hence restricting air flow?

It is better not to have frost, but that is not going to happen. You will have frost in cold weather and we want the coil to frost fully and evenly.

[Gary]

I'm not planning to use this when there is hot weather as it doesn't need it. The plan is to just use it in winter and the solar panels in summer with a changeover during spring/autumn.

Excellent. That makes the fine tuning far less complicated. :)

[Gary]

With SCT at roughly 42C and water in temp at 22C, this gives us a cond TD of 20C. This is only borderline high. There may be hope for this system yet. :)

[Gary]

Given the stipulation that the system is not used in warm weather, we can run it up to full capacity without endangering the compressor... however... the condenser TD is already running borderline high with a light load. The condenser is the weak link in the chain. I would build another identical condenser and pipe it in parallel with the first. This would be a good thing even if we stayed with the light load.

And given increased condenser capacity, we could take steps to load this system up. We could install a TXV/wMOP and then crank the fan back up to full speed.

[Gary]

Hmmm... TXV sizing is not my forte. Perhaps others could jump in here.

I would guesstimate that the Fujitsu AOG25 capacity in A/C is about 7Kw... and in med/low temp operation would be about 3-4Kw. Am I close?

[Acuario]

The compressor is a Tecumseh AW5532A / AW108KT-027-B4, can't find any info on it but the AWA5532EXV is 9.144Kw, input 3Kw so maybe this is the current equivalent (verified it takes 3Kw by connecting an electric meter in series).

I'll build heat exchanger MK1 No2 and connect it in series as soon as I can.

Thanks to all for the help so far, it's been fun!

[MikeHolm]

Parallel, pipe it is parallel. I would think the pressure drop is important. Des, Gary?

[Gary]

Parallel, pipe it is parallel. I would think the pressure drop is important. Des, Gary?

Yes... it should be piped in parallel, not series.

[Gary]

Did you switch the fan to low speed?... take new pressure and temperature measurements?

[Acuario]

No time to do much today but I've fitted a valve in the LP side, recharged and took this photo of the guages. It's dark now so I can't do any more tonight. The ambient was around 9'C, water at 23'C.

Picture here:
http://www.costadoradaholiday.com/guages_1.jpg

[Acuario]

Parallel, pipe it is parallel. I would think the pressure drop is important. Des, Gary?

Sorry, typo - meant to say parallel - no space to put it in series!:eek:

[Acuario]

Parallel, pipe it is parallel. I would think the pressure drop is important. Des, Gary?

Sorry, typo, meant to say parallel - no room to fit one in series..

[Acuario]

Hi,
here are some results following addition of the valve to measure suction line pressure and after adding a bit of refrigerant to take it back to roughly what it was before adding the valve.

Ambient temperature: 10'C
Water temperature: 22'C

Fan full speed
HP pressure: 270psig
LP pressure: 48psig
Temp at compressor 150mm: 98.8'C
Temp at condenser input: 93.9'C
Temp at condenser output: 33.4'C
Temp at evaporator input: -4'C
Temp at evaporator output: 9.6'C
Frost on evaproator: about 30%

Fan slow speed
HP pressure: 245psig
LP pressure: 39psig
Temp at compressor 150mm: 117'C
Temp at condenser input: 106'C
Temp at condenser output: 31.8'C
Temp at evaporator input: -10'C
Temp at evaporator output: 9.2'C
Frost on evaporator: about 60%

Hope the figures make sense!

Nigel

[Gary]

Hi,
here are some results following addition of the valve to measure suction line pressure and after adding a bit of refrigerant to take it back to roughly what it was before adding the valve.

Ambient temperature: 10'C
Water temperature: 22'C

Fan full speed
HP pressure: 270psig
LP pressure: 48psig
Temp at compressor 150mm: 98.8'C
Temp at condenser input: 93.9'C
Temp at condenser output: 33.4'C
Temp at evaporator input: -4'C
Temp at evaporator output: 9.6'C
Frost on evaproator: about 30%

Fan slow speed
HP pressure: 245psig
LP pressure: 39psig
Temp at compressor 150mm: 117'C
Temp at condenser input: 106'C
Temp at condenser output: 31.8'C
Temp at evaporator input: -10'C
Temp at evaporator output: 9.2'C
Frost on evaporator: about 60%

Hope the figures make sense!

Nigel

Add refrigerant slowly until the evap is fully frosted. The frost can be on the suction line, but not all the way back to the compressor. Then show us the new readings.

[Acuario]

What fan speed, slow or full?

[frank]

Have you fitted a TEV yet or are you still trying to make it work with the capillary?

The compressor won't last long with those temps ....... 100C+

[Gary]

Have you fitted a TEV yet or are you still trying to make it work with the capillary?

The compressor won't last long with those temps ....... 100C+

I agree. Adding refrigerant will bring down the discharge temp, but it will also make the condenser even less efficient than it already is. Adding a TEV aka TXV will overload the condenser. This system needs expanded condenser capacity as well as a TEV.

Until then, the best we can do is add refrigerant and/or shorten the cap tube.

[Gary]

What fan speed, slow or full?

Unless/until you have added condenser capacity... slow the fan speed.

[desA]

Ambient temperature: 10'C
Water temperature: 22'C

Fan full speed
HP pressure: 270psig -> Tc,sat~ 50.46'C
LP pressure: 48psig -> Te,sat ~ -4.244'C
Temp at compressor 150mm: 98.8'C
Temp at condenser input: 93.9'C
Temp at condenser output: 33.4'C -> SC=17.06K
Temp at evaporator input: -4'C
Temp at evaporator output: 9.6'C -> SH=13.84K
Frost on evaproator: about 30%

Fan slow speed
HP pressure: 245psig -> Tc,sat ~ 46.49'C
LP pressure: 39psig -> Te,sat ~ -8.752'C
Temp at compressor 150mm: 117'C <========= !!!!
Temp at condenser input: 106'C
Temp at condenser output: 31.8'C -> SC=14.69K
Temp at evaporator input: -10'C
Temp at evaporator output: 9.2'C -> SH=17.95K
Frost on evaporator: about 60%

Hope the figures make sense!

Nigel

System seems to be overcharged wrt condenser, undercharged wrt evaporator. Add lots of extra surface to condenser pipe!!!! Then lets see what gives.

[desA]

Yes... it should be piped in parallel, not series.

I'd agree. Will need decent end manifolds to get decent distribution.

[Acuario]

Just bought the bits to make the second condenser so will hopefully make it tomorrow. Still using a capillary but my suppliers have TXV's so will get one and try to work out how to install it. I guess it replaces the capillary, the one he showed me had 2 ports, what looked to be a point to adjust it and what looked like a bulb on the end of a thin coil. Where does this go?
Nigel

[Acuario]

Have you fitted a TEV yet or are you still trying to make it work with the capillary?


Ok, just watched a video on TXV's and their construction. Looks like it'll be an interesting addition. So, as usual some questions;

1. What rating of TXV do I need
2. Do I need one that has the ability to be externally equalized
3. At what point on the suction line does the bulb need to be placed.
4. How do I attach the bulb, a jubilee clip/tie wraps/tape?

Thanks to all!

Nigel

[monkey spanners]

Ok, just watched a video on TXV's and their construction. Looks like it'll be an interesting addition. So, as usual some questions;

1. What rating of TXV do I need
2. Do I need one that has the ability to be externally equalized
3. At what point on the suction line does the bulb need to be placed.
4. How do I attach the bulb, a jubilee clip/tie wraps/tape?

Thanks to all!

Nigel

1. I'd base the TXV capacity on the cooling duty of the original air con system.
2. Externally equalised would be best.
3. Just after the outlet of the evaporator. The equalising line is piped to just after the bulb.
4. The valve should come complete with a clamp, but a jubilee clip will get you going. The bulb needs to be insulated too.

Most TXV's have an instruction sheet in the box or printed on the box itself.

Jon :)

[nevgee]

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!


The clean copper in your system could also be due to the water scouring the metal and slowly erroding it. If the Ph is low, say less than 0.7 there will be a tendancy for the water to leech metal components. Hence shiny copper.

Oxide layers that form on copper in pool atmospheres are usually "Verdi Gris" which does not provide a protective layer. Over time pin hole penetration will occure, and with the refrig pipework, oil will slowly weep through causing the verdis gris to become pasty to touch.

On another note, There is now a following of operators using Copper ionisation in the pool water instead of chlorine. I believe it's a cheaper method. I have no invormation but yuo can search and find many sites that sell this product.

[Acuario]

1. I'd base the TXV capacity on the cooling duty of the original air con system.

I've no idea what that was, there is no label or anything. Only the model number and initial charge. The compressor is 3Kw and a COP of 3 so what would I expect, 9Kw cooling? From the video they talked about 'tonnes', how does this relate? What measurement do TXV's come in? Kw/Tonnes/something else? :confused:

[nevgee]

Some years back, a friend asked me to have alook at his fathers pool heater.

A basic set up with a condensing unit, maybe 1hp, situated within his large green house and a stainless steel cylinder with copper discharge pipework coil running through it. It looked like a home made jobby.

When I connected my gauges on the suction rotolock, water came out :eek:

When It was stripped in our workshop, the discharge copper coil was disintegrating,

I managed to replace it, dry out the existing condenser, rebuild it and re-install it back into his greenhouse. It's still going strong :D

I used 316 S/S tubing though, not copper in the re-build.

I haven't worked on any S & T HX's for pools since, only brazed plate HX's

I have come across many situations simillar to that you mention. We find if we test the water the PH tends to be down below 0.7. At this level the water leeches all metal components. In some cases I've had to return and redo the whole wash out within months of the first repair. One guy was an industrial chemist and thought checking his water 6 monthly would be adequate? every week is essential at the min.

I find worse case is when there are lots of children using the pool for other than swimming. Air born Chloramines rot all the metal work, stainless as well.

[monkey spanners]

I've no idea what that was, there is no label or anything. Only the model number and initial charge. The compressor is 3Kw and a COP of 3 so what would I expect, 9Kw cooling? From the video they talked about 'tonnes', how does this relate? What measurement do TXV's come in? Kw/Tonnes/something else? :confused:

A ton is 12000 btu is 3.5Kw.

Whats the model no. and make of your unit?

What make of expansion valve did they have at the wholesalers?

[nevgee]

Sounds like it to me - according to nobility table stainless steel is quite anodic and far away from copper which is cathodic with the result being that the copper will corrode.

There is always that possibility but the majority of corrosion in swim pool apps is not due to electrolytic wasting but chemical reaction. That's why it is essential the chemical balance of the water is kept spot on.

[Acuario]

Whats the model no. and make of your unit?

What make of expansion valve did they have at the wholesalers?
Fujitsu AOG25AWNL. Tecumseh AW5532A compressor.

I can't remember the make of the valves, they only had one make so little choice!

[Acuario]

Ok, went to the wholesalers to ask what they had. The units they sell are Danfoss TX2 devices. He asked which one and I had no idea! So, over to you guys!

[frank]

Your unit is rated at 7.2Kw nominal cooling so your TEX2-(N) needs to be externally equalised with a No.4 orifice (8Kw nominal)

The valve body is the DAN112. The orifice is a DAN208.
The valve will have 3/8" and 1/2" flare connections. The equalising port will have a 1/4" flare connection.
Do you have a flaring tool?

Don't buy the TX2 as this is internally equalised

[Acuario]

Yes, have a flaring tool so no problem. Will go and see if they have this one in stock in the morning and get it installed if they do.

Work interrupted pleasure today so I'll be building the second heat exchanger tomorrow. Have the unit turned off at the moment as I don't want to damage the compressor with excessive heat.

Beautiful sunny weather here at the moment so the solar panels are working hard.

[Acuario]

Your unit is rated at 7.2Kw nominal cooling so your TEX2-(N) needs to be externally equalised with a No.4 orifice (8Kw nominal)

The valve body is the DAN112. The orifice is a DAN208.
The valve will have 3/8" and 1/2" flare connections. The equalising port will have a 1/4" flare connection.
Do you have a flaring tool?

Don't buy the TX2 as this is internally equalised
What part numbers? There are several, I can't find any that has a reference of DAN112 or DAN208, the orifice I guess is part 68-2007.
http://www.kulde.org/CH8/TE2.pdf

Thanks!

[nevgee]

Just bought the bits to make the second condenser so will hopefully make it tomorrow. Still using a capillary but my suppliers have TXV's so will get one and try to work out how to install it. I guess it replaces the capillary, the one he showed me had 2 ports, what looked to be a point to adjust it and what looked like a bulb on the end of a thin coil. Where does this go?
Nigel


Based on your compressor model. The compressor duty at
4.5 barg suction
18 barg disch
has a duty 7.8kW. R22

Expansion valve required
Danfoss TEX2N (without MOP) has duty of 8.9 kW with press drop of 10 b evap at 5C. when using orifice No 03.
As you're able to braze then the better option of valve would be one you can braze into the sytem.

TEXN part number 068Z328400 (solder)
plus
Orifice 03 Part number 068 209300
plus 3/8 solder adaptor 068 206066


There is a 25% leaway with these valves on their duty and of course you may need to adjust the superheat once up and running.

:)

[nevgee]

Your unit is rated at 7.2Kw nominal cooling so your TEX2-(N) needs to be externally equalised with a No.4 orifice (8Kw nominal)

The valve body is the DAN112. The orifice is a DAN208.
The valve will have 3/8" and 1/2" flare connections. The equalising port will have a 1/4" flare connection.
Do you have a flaring tool?

Don't buy the TX2 as this is internally equalised


Sorry to butt in here Frank.
I think you may be quoting nominal duty for the orifice wich is only based on a 2 bar dp across the valve. this application is most likely to have 10 bar dp across the valve. in that case an orifice No. 03 would be most suited as it's duty is 8.9 kW Whereas the no.04 orifice will have a duty of 13.3 kW ... too high I think.

[nevgee]

links where you can get details of the Danfoss valves.

http://www.ra.danfoss.com/TechnicalInfo/Literature/Manuals/01/PBAA0A402_T2.pdf

http://www.ra.danfoss.com/TechnicalInfo/Literature/Manuals/01/DKRCCPDAA0A402.pdf

[nevgee]

What part numbers? There are several, I can't find any that has a reference of DAN112 or DAN208, the orifice I guess is part 68-2007.

Thanks!

See above post :)

[nevgee]

This link may be helpfull ... Danfoss "Fitters notes" gives instructions on Expansion valves and setting them up.

http://ra.danfoss.com/TechnicalInfo/literature/manuals/01/PF000G102_chapter_01.pdf

[nevgee]

Parallel, pipe it is parallel. I would think the pressure drop is important. Des, Gary?


I think you're quite right here. Does Acuario have the necessary information to pipe up the second condenser, taking into consideration the gas flows to ensure even balancing and equal flow through both condensers?
Perhaps someone has got some typical pipework arrangements that he could follow. Otherwise I fear he may hook up the 2nd condenser and find his gas flows are wrong.

:)

[nevgee]

Attached Danfoss pages with TEX selection data

[frank]

I was using the RPW Catalogue :confused:

[nevgee]

I was using the RPW Catalogue :confused:


Maybe you need to refresh your glass and try different brew? ;)

[Acuario]

Well I opted for Heat Exchanger MKII instead of a second MKI in parallel, I could always parallel them up if necessary.

MKII has more coils; 3 to be precise, coil 1 wound on a 32mm former, coil 2 wound on a 50mm former and coil 3 wound on a 75mm former. All then fitted one inside the other and linked at either end. The pipe in each coil is 1/4" diameter. Coil 1 is about 6m long, coil 2 about 9m long and coil 3 about 15m long (now you're going to tell me they should all be the same!).

They are all contained in a 110mm diameter pipe 68cm long.

As I write I'm waiting for the glue to finish drying. I'll post pictures later.

My supplier isn't open saturday afternoons so I'll go and order/purchase the TXV on monday.

[nevgee]

Well I opted for Heat Exchanger MKII instead of a second MKI in parallel, I could always parallel them up if necessary.

MKII has more coils; 3 to be precise, coil 1 wound on a 32mm former, coil 2 wound on a 50mm former and coil 3 wound on a 75mm former. All then fitted one inside the other and linked at either end. The pipe in each coil is 1/4" diameter. Coil 1 is about 6m long, coil 2 about 9m long and coil 3 about 15m long (now you're going to tell me they should all be the same!).





Ideally, yes. You really need to try to ensure the gas flows are equal through the sections of the condenser.

Had you not considered using a tank instead of a pipe to contain the coils?

[nevgee]

I have come across many situations simillar to that you mention. We find if we test the water the PH tends to be down below 0.7. At this level the water leeches all metal components. In some cases I've had to return and redo the whole wash out within months of the first repair. .

Sorry for my error ..... should have read 7.0 not 0.7.

The ph of a swimpool water should ideally be 7.4

[MikeHolm]

If you are able to ensure roughly even flow over each of the coils, they should be of roughly equal lengths of tubing although, I believe, the coil with a larger helical diameter will have a slightly smaller pressure drop.

[Acuario]

Here we go again, a disaster, bad weather and work got in the way but at last I'm off again..
The disaster - I managed to leave a small unbrazed hole in HX MKII and flooded my evaporator etc :eek:. I also managed to dump my charge of R22 into the pool at the same time :eek:. So, a change of refrigerant and a bit of a clean up was in order..
Blew everything out with Nitrogen and it is up and seems to be running again. As there was no refrigerant left, and I was concerned about any moisture in the compressor (I'm sure there was) I added a filter dryer and at the same time cut out the capillary and installed a TXV.

The TXV is a Danfoss TX2, 068Z3206 and I fitted orifice No. 03, but without filter as that was all he had.

So, it's running again with a new refrigerant, RS44 (R424A), slightly different PT characteristics but it's a drop in replacement.

Measurements are (fan at full speed):
Compressor exit temperature: 53.5'C
Pressure 112psig
Condensor entry 53.1'C
Condensor exit 16'C
TXV entry 14'C
TXV exit (evaporator entry) -1.8'C
Evaporator exit 5.9'C
Suction pressure 37psig

Tuning advice welcome!

Nigel

[Gary]

Here we go again, a disaster, bad weather and work got in the way but at last I'm off again..
The disaster - I managed to leave a small unbrazed hole in HX MKII and flooded my evaporator etc :eek:. I also managed to dump my charge of R22 into the pool at the same time :eek:. So, a change of refrigerant and a bit of a clean up was in order..
Blew everything out with Nitrogen and it is up and seems to be running again. As there was no refrigerant left, and I was concerned about any moisture in the compressor (I'm sure there was) I added a filter dryer and at the same time cut out the capillary and installed a TXV.

The TXV is a Danfoss TX2, 068Z3206 and I fitted orifice No. 03, but without filter as that was all he had.

So, it's running again with a new refrigerant, RS44 (R424A), slightly different PT characteristics but it's a drop in replacement.

Measurements are (fan at full speed):
Compressor exit temperature: 53.5'C
Pressure 112psig
Condensor entry 53.1'C
Condensor exit 16'C
TXV entry 14'C
TXV exit (evaporator entry) -1.8'C
Evaporator exit 5.9'C
Suction pressure 37psig

Tuning advice welcome!

Nigel

112 psig for R22 (from P/T chart) is about 19C-16C (exit temp) =3K subcooling. Add refrigerant slowly until the subcooling is about 8.5K.

[Acuario]

I had a small leak so had to remove the gas, fix it and re-gas. Obviously readings changed...
I also spotted I put a wrong value - too many scribbles on my bit of paper!
A new bit of paper so no confusion!
Readings are:

Ambient: 15'C
Water: 20'C
Exit pressure: 167psig
Exit temp: 64'C
Condensor entry: 61'C
Condensor exit: 26'C
Evap exit: 11'C
Suction pressure: 38psig

So, following the above I have subcooling:
32.2 - 11 = 21.2K

Is this too high? Should I try to reduce it?

Nigel

[Gary]

I had a small leak so had to remove the gas, fix it and re-gas. Obviously readings changed...
I also spotted I put a wrong value - too many scribbles on my bit of paper!
A new bit of paper so no confusion!
Readings are:

Ambient: 15'C
Water: 20'C
Exit pressure: 167psig
Exit temp: 64'C
Condensor entry: 61'C
Condensor exit: 26'C
Evap exit: 11'C
Suction pressure: 38psig

So, following the above I have subcooling:
32.2 - 11 = 21.2K

Is this too high? Should I try to reduce it?

Nigel

That's 32C-26C=6K

[nevgee]

I had a small leak so had to remove the gas, fix it and re-gas. Obviously readings changed...
I also spotted I put a wrong value - too many scribbles on my bit of paper!
A new bit of paper so no confusion!
Readings are:

Ambient: 15'C
Water: 20'C
Exit pressure: 167psig
Exit temp: 64'C
Condensor entry: 61'C
Condensor exit: 26'C
Evap exit: 11'C
Suction pressure: 38psig

So, following the above I have subcooling:
32.2 - 11 = 21.2K

Is this too high? Should I try to reduce it?

Nigel

38psig = 2.6 barg = -9C sst Too low
super heat -9 -11 = 20C Far too high

Add gas as Gary suggests and open TX valve to reduce Sh. approx one full turn counter clockwise will give 4 C .. so 2 to 3 full turns might do the trick. Check instructions on box. Do it at 1 turn at a time and allow 10 - 15 mins for the system to settle down each time.