Extremely simplistic HP pool heater
 

I understand the basic refrigeration/heat pump thermodynamics (I had 1 class in thermo back in college about 40 years ago. I don't think the basics have changed ). I have done a lot of reading here and learned/re-learned a lot, but I still have no "hands on" experience. (yet !).

My neighbor has an in-ground swimming that can only be used about 3 months of the year due to our local climate. The gas fired pool heater died a long time ago. He also has about a 2.5 A/C unit.

IN THEORY, if we could plumb a refrigerant/water heat exchange between the compressor and the condenser and then pipe the water from the pool filet through the other side of the HX it would heat his pool and cool his house, correct ?

I want this as simple as possible, so I am thinking full manual control. If there is no cooling demand in the house, no pool heating occurs. Even if there is cooling demand in the house, if the filter pump is not turned on, no pool heating occurs.

Other than all of the issues with plumbing both the pool water and the refrigerant to and from the HX, what is wrong with this idea ? My biggest concern is damaging the HX when there is no water flow and the compressor is running.


Sidebar for a newbie :

• Can some one link to a discussion on commercial tube-in-tube coil versus plate HX ?
• In an application like a pool heater, where you have a theoretical "infinite sink" how do you size the HX by the size of your wallet ?
• How do you calculate the additional refrigerant required ?

I'm no expert, but...

Yep. I did something very basic like this several years ago with a window unit. Basically pumped pool water over the condenser and caught some of it to go back into the pool. It worked quite well, aside from looking like a disaster and leaking water all over. :) The air inside will be colder, and it will probably use less watts, too!

That would be my concern also. You don't want to run it if there is no water flow.

It will have to do with the pressures and temperatures you see in your system. You will need a cheap set of A/C gauges for charging to read when it is full.

For a heat exchanger, you could use something as simple as a length of copper tubing submerged in water. (30 feet?)

A simple coil of copper would work and could be put in easily.

There are a significant number of threads that describe this situation. Go for it.

Steve

I have read several of those but I have not found the answers to my questions/issues.

How does the energy cost of this compare with the red neck pool heater of a length of black poly pipe & a pump , as a solar system ?

Seems like the problem with what was described is , as the weather gets cooler , the more pool heat will be needed , while less house cooling will be needed ?

God bless
Wyr

IMHO you should not have a problem doing this at all. By the time it is warm enough outside to require air conditioning, there would be no chance of frost. I recommend running a coaxial heat exchanger as a desuperheater. Due to the chlorinated pool water, a cupronickel or stainless steel refrigerant tube is necessary for longevity.

https://surpluscityliquidators.com/v..._TON_COAX_COIL

The pool plumbing could be tapped into like another jet and the hx could be setup like a solar drainback system. All that would be needed is some sort of vacuum breaker at the high point in the plumbing. When the pool water was not being circulated, the ac unit would rely on the original condenser. When the pool pump was running, the added hx would heat pool water when the compressor was active. The hx wouldn't burn up when it was idle, but when it ran it would dramatically increase the efficiency of the ac unit.

You are 100% correct ! This is why it has to be an addon to an existing system and it has to be done inexpensively.

We we are located, pool heat could be used well into June.

Something like that is exactly what I was thinking of ! I'll have to remember the proper terminology - coaxial coil HX.

That is a good tip !

This is my biggest concern.

How do you calculate the additional refrigerant required ?

With a capillary tube system, you charge by superheat. With a TXV you charge by subcooling. I would do the charging while the added hx was inactive. All manufactured units have both initial charge weight figures and superheat/subcool recommendations and specs in the install manual. Lots of them have temp/pressure charts listed for a range of common operating conditions also.

With a retrofit or mod into an a/c only unit, I wouldn't even worry about it if you're going to have a short length of plumbing connecting the coax exchanger. I would charge by weight, then take a superheat reading. If it was close to factory specs, I would let it ride. If I had time to burn, I might try to optimize the charge. Even then, not much extra refrigerant would be needed, maybe an ounce or three.

The main thing with this scenario is indoor airflow. If you increase the efficiency of the outdoor unit much, you may end up with a very cold evaporator. Especially with a cap tube system, the reduction in high side pressure could freeze it quickly if there's not enough air moving through it.

Newbie here !

Yes, the plan would be to to mount the HX as close as possible to the compressor outlet.

I don't understand "charge by weight" and where do you take "a superheat reading" ? (Is that the temp coming out of the compressor ?)