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Acuario · 05-14-11, 01:38 PM

Ok, so here is my experience in this thread as suggested by AC Hacker.

At the beginning of the year I decided to heat my swimming pool. I had it covered last year to allow me to use it longer but I then decided it might be an idea to try to use it all year so I looked around to see what was available and came across heat pumps. As I've spent the last few years installing split air conditioners I had all the tools I needed but had never even tought about using an air conditioner to heat water, so I started investigating.

The commercial units are quite expensive and I love a challenge. Someone I knew was selling an old air conditioner for 30 euros so I bought it without knowing anything about how it might be made to heat the pool.

A bit more investigation and lateral thinking and finding out how air conditioner/heat pumps worked and I came up with a plan.

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 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 has two circuits through it that are linked at either end. The liquid end I left but the gas end I cut and braised to feed the two tubes into a 1/2" tube to connect back to the gas side of the compressor.

MK 1 heat exchanger was interesting. I built 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 had no idea how long it would need to be so as I have limited space I just made it to fit the space which is about 90cm.

To elaborate on the heat exchanger construction, there needs to be 2 connections either end, one for water and one for refrigerant. Water is easy enough as pools are usually piped with 50mm pipe and it can all be glued together to provide a water tight seal. The refrigerant pipes, however, have to pass through the end caps and have a watertight seal. My solution to this was to buy a tank connector - is that what they are called? Basically it is a threaded tube that has a flange on one end and a set of washers and nut. You drill a hole in the tank (in my case the end cap) and the flange plus washers provide a watertight seal. If you look at the 1st and 4th photos on the second row of photos on my website (see address below) you'll see the end caps and tank connector. The refrigerant pipe passes through the middle of the tank connector and the gap is filled with solder. The whole assembly is then inserted into the main body of the heat exchanger, glued up and the nut tightened down to create a seal.

Commercial units seem to have titanium heat exchangers but I have no source of titanium pipe so it's copper. I was aware of the potential problem of corrosion but I've been pumping chlorinated water through copper solar panels for several years without problem. It all depends on pH values! To be on the safe side I have a piece of pipe in the filter basket of my pool pump - so far it shows no sign of anything adverse.

The original unit had R22 as the refrigerant but this is now

Banned for use in any new project or machine
Almost impossible to buy from anywhere to charge or refill a unit

Following a mini disaster I had with MK2 heat exchanger I was forced to use a drop in replacement and I opted for RS-44 as you don't then need to change anything and the PT is pretty similar to R22.

I've written some (not all yet) of it up with photos of the project on my website http://www.tortosaforum.com/poolheater.html that describes how I modified the air conditioner and built MK1 and MK2 heat exchangers to heat the pool.

I have no idea what the efficiency of the units is but they do heat the water really quickly! Maybe I'll try and work it out sometime as I'd love to know.

As a suggestion to anyone looking to try something similar, go for a conventional single phase compressor as you then don't need any control circuitry. The newer generation of inverter machines use brushless dc motors (bldc) which have complex control systems to vary the speed of the compressor motor. I'm might try one of these out at some point but for the moment I'm sticking with a basic unit as my projects don't need that level of control.

Nigel

05-14-11, 01:38 PM	#6
Acuario Apprentice EcoRenovator Join Date: May 2011 Location: Tortosa, Spain Posts: 221 Thanks: 2 Thanked 81 Times in 46 Posts	Pool heater using recycled air conditioner Ok, so here is my experience in this thread as suggested by AC Hacker. At the beginning of the year I decided to heat my swimming pool. I had it covered last year to allow me to use it longer but I then decided it might be an idea to try to use it all year so I looked around to see what was available and came across heat pumps. As I've spent the last few years installing split air conditioners I had all the tools I needed but had never even tought about using an air conditioner to heat water, so I started investigating. The commercial units are quite expensive and I love a challenge. Someone I knew was selling an old air conditioner for 30 euros so I bought it without knowing anything about how it might be made to heat the pool. A bit more investigation and lateral thinking and finding out how air conditioner/heat pumps worked and I came up with a plan. 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 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 has two circuits through it that are linked at either end. The liquid end I left but the gas end I cut and braised to feed the two tubes into a 1/2" tube to connect back to the gas side of the compressor. MK 1 heat exchanger was interesting. I built 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 had no idea how long it would need to be so as I have limited space I just made it to fit the space which is about 90cm. To elaborate on the heat exchanger construction, there needs to be 2 connections either end, one for water and one for refrigerant. Water is easy enough as pools are usually piped with 50mm pipe and it can all be glued together to provide a water tight seal. The refrigerant pipes, however, have to pass through the end caps and have a watertight seal. My solution to this was to buy a tank connector - is that what they are called? Basically it is a threaded tube that has a flange on one end and a set of washers and nut. You drill a hole in the tank (in my case the end cap) and the flange plus washers provide a watertight seal. If you look at the 1st and 4th photos on the second row of photos on my website (see address below) you'll see the end caps and tank connector. The refrigerant pipe passes through the middle of the tank connector and the gap is filled with solder. The whole assembly is then inserted into the main body of the heat exchanger, glued up and the nut tightened down to create a seal. Commercial units seem to have titanium heat exchangers but I have no source of titanium pipe so it's copper. I was aware of the potential problem of corrosion but I've been pumping chlorinated water through copper solar panels for several years without problem. It all depends on pH values! To be on the safe side I have a piece of pipe in the filter basket of my pool pump - so far it shows no sign of anything adverse. The original unit had R22 as the refrigerant but this is now Banned for use in any new project or machine Almost impossible to buy from anywhere to charge or refill a unit Following a mini disaster I had with MK2 heat exchanger I was forced to use a drop in replacement and I opted for RS-44 as you don't then need to change anything and the PT is pretty similar to R22. I've written some (not all yet) of it up with photos of the project on my website http://www.tortosaforum.com/poolheater.html that describes how I modified the air conditioner and built MK1 and MK2 heat exchangers to heat the pool. I have no idea what the efficiency of the units is but they do heat the water really quickly! Maybe I'll try and work it out sometime as I'd love to know. As a suggestion to anyone looking to try something similar, go for a conventional single phase compressor as you then don't need any control circuitry. The newer generation of inverter machines use brushless dc motors (bldc) which have complex control systems to vary the speed of the compressor motor. I'm might try one of these out at some point but for the moment I'm sticking with a basic unit as my projects don't need that level of control. Nigel Last edited by Acuario; 09-17-11 at 06:13 AM..