Using an A/C unit to heat the swimming pool

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Old 02-21-19, 01:43 PM
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Using an A/C unit to heat the swimming pool

Hi

I have a old three-phase A/C of about 50,000 BTU.

Since pool heat pumps are very expensive, I thought to use a gas/water heat exchanger. So that he would replace the inner unit.

So that when the air conditioner will work in heating mode, the hot gas will pass through the heat exchanger. And warm the water that flows through it (from the pool pump).

Can such a conversion be made, and is there a need for special adjustments? (Pressure, gas type, temperature, etc.)

I've attached a link to a heat exchanger I've seen on the net:

https://he.aliexpress.com/item/17KW-...348584888.html

Thanks
 
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Old 02-21-19, 03:38 PM
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Sounds like a "drive yourself crazy" project... It might work for a hot tub, but swimming pool heaters are generally in the 100,000 - 500,000 BTU range.
Quick guesstimate for 50,000 BTU and an average pool is that you'd get a heat rise of about 1/4 of a degree per hour. Not gonna work the way you want.

I found that the best way to warm up my inground pool in the spring/summer was to wait for a warm day and route the return through a fire-hose-style fogger-nozzle pointed straight up.

Fine spray has a huge surface-to-volume ratio, pull the 45 degree water from the bottom and spraying on a 70 degree day raised the water temperature by about 10-15 degrees over 24 hours.
 

Last edited by Hal_S; 02-21-19 at 03:56 PM.
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Old 02-21-19, 04:08 PM
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It’s possible, but you’ll need a lot more then just a heat exchanger. And a 3 phase unit isn’t going to do you much good if this is at your house.
You’ll need a heat pump.
You’ll likely be most of the way to the cost of a purpose built pool heat pump by the tome it’s done.
 
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Old 02-21-19, 04:31 PM
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I've considered doing that too but an exchanger that is not eaten by chlorinated water is the most expensive part of the system. I looked at the cost to do it versus the gains. There wasn't enough in the gain column to warrant it.
 
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Old 02-21-19, 04:41 PM
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If you're looking at adding ~50,000 BTU of heating, that's within the range of solar pool covers...

Estimate up to 25,000 BTU from a 5' x 5' solar cover.

https://www.poolproducts.com/p/solar-sun-square
 
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Old 02-22-19, 11:20 AM
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HI
thanks for the answers.

some more details about this project that I think need to be shown:

1. the pool is 22000 liters (small pool)

2. I have a solar cover and solar heating system that can heat the pool in a sunny day. but I would like to use it at colder seasons

3. the A/C I use is a separate unit that will be placed near the pool and operate for this purpose only.
 
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Old 02-23-19, 07:11 AM
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A problem you will run into is that you definitely heat the water with the heat exchanger you have shown but on cooler days where will the heat come from?
All any refrigeration device does is transfer heat from one place to another and if it is cooler weather what heat is the air conditioner going to move?
You will heat the water on hot days when the air conditioner is running but will need some kind of electric back up on cooler days.

Hardly seems worth the bother.
 
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Old 02-23-19, 07:53 AM
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I think people are worried because we're seeing the wrong terminology.

Originally Posted by kipod earlier
So that when the air conditioner will work in heating mode, the hot gas will pass through the heat exchanger. And warm the water that flows through it (from the pool pump).
Um, you can't pass warm chlorinated pool water through a commercial A/C heat exchanger (for long) because it will rust out.

Originally Posted by kipod recently
3. the A/C I use is a separate unit that will be placed near the pool and operate for this purpose only.
If this is a straight 50,000 BTU A/C unit, NOT a heat pump, then the system is going to be engineered with air cooling in mind. Matching the heat-flow of air over fins with pool water and a heat exchanger is, going to be "interesting".

The concern is, with the water-flow-modification and cold water, it will pull TOO much heat from the refrigerant and the compressor will ice over. With the water-flow-modification and warmed water, it will pull TOO little heat, the system will overheat.

An air-cooled A/C system is engineered for heat flow to air, e.g. variable speed fans. You'll need some sort of variable speed pump and temperature feedback calibrated to the water cooled system.
 
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Old 02-23-19, 01:03 PM
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the heat exchanger is made of titanium. so it made to work with a chlorinated pool water.

about the compressor over heat/ freeze . I understand the I will need to connect the heat exchanger to an arduino controller. that will give temp feedback and will control the water flew, It can be made with variable speed pump or with electric valve that will bypass some of the circulation when it open. so the flew through the exchanger will decrees ( I can use 2 valves and then I will have 3 flew "speeds").

or maybe I can use the original electric card ( after changing the sensor) by taking it apart from the inner unit to control that?
 
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Old 03-03-19, 10:56 PM
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need some help

Hey.

I notice that I was not clear enough about my intentions, which led to a lack of understanding. Part of the lack of understanding comes from the fact that although I have some technical knowledge, I am not a AC technician, so the terms I use may be confusing and even misleading.
In addition, my native language is not English either.

Nevertheless, I would be happy to use your knowledge and support in this forum to understand the issue and make as few mistakes as possible.

First of all, it is important to note that this is indeed a "crazy project" that I play with.

Second, heat pump prices (around 17KW output) in Israel are very expensive and can raise about $ 3,000 and even more. Making this project worthwhile.

The system I'm trying to build is based on an external air conditioner unit. that I'm trying to convert to a heat pump. And to heat a swimming pool with a capacity of 22 cubic meters.

It should be remembered that Israel is usually a warm country, winter temperatures usually do not fall below 10 degrees Celsius, and this is only on very cold days.

In addition, the pool is located in a relatively closed building (greenhouse)

There is already a solar heating system for the pool, but it is effective only when there is direct sunlight, ie during the summer months. So I need a solution for heating in the winter.

My thought is to use an external unit of air conditioner. To be used as the evaporator and connect it to a heat exchanger in place of the original internal unit (which in the case of heating functions as a condenser).

The heat exchanger I have is designed to work with pool water and is made of titanium. So that on the one hand there is a passage from pool water and on the other hand a passage of gas.

Since the original internal unit (which I do not own) also included temperature control and feedback from the various parts, I will need to add a replacement.

In addition, the external unit included a capillary tube at the exit of the condenser, and I have to find a solution to that as well.

I attach some data and drawings of the condenser and the original AC from its manuel book

I would be happy if I could get guidance and help here, and of course clarify and give information that might be missing here.
 
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Old 03-04-19, 11:40 AM
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suggested system diagram

A diagram of the planned system is attached.

Questions I'd be happy to answer:

1) I thought to replace the capillary tube that was originally in the EXV. If so, which expansion valve should I use?

2) What types of control and feedback should I add? High / Low Pressure Pressostat?
Thermostat?

Are there any additional components missing in this system?
 
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Old 03-04-19, 02:49 PM
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Sorry.... you're basically on your own. You are doing something non conforming and will need to experiment. Your looking for a design engineer and I don't believe there are any here.
 
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Old 03-05-19, 05:13 AM
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I agree.
Your project is possible to accomplish but most definitely not for a novice or DIY'er.
Plus, because of refrigerant handling laws we do not discuss working on these systems.


I can appreciate wanting to save money by not purchasing a replacement pool heater but you need to rethink trying to engineer hacking a simple AC unit.
Besides the information needed to do this the components you need to purchase are not cheap and considering your chances of it working well I feel spending money on this experiment would be wasted $$$.


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