Heat transfer

Nice idea...

Sorry no simple, cheap, practical idea. But you should be able to build solar heating for the hot tub as a cheap easy fun project....

Good luck, have fun!

Why not run a parallel loop from the tub to the coil to extract free heat .

Easy to say...not sure if it's cheap and easy to do...but could be fun!

Just don't stand in the hot tub whilst using power tools...

Depends on how hot the hot tub is, doesn't it?

Your HVAC dealer should be able to provide you with a condenser coil that can be put in water. There are condensers for heat pumps that will deposit unwanted heat or gather heat from ground water or even from the bare earth itself. Put the coil in a large bucket, drop a submersible pump in the bucket and drape the hose over the rim of the hot tub. You could have a siphon hose returning to the bucket from the drain of the hot tub if you want to circulate water. The water coming off the coil might be quite hot, though. You'd need to set up some kind of heat regulator so that you don't scald yourself. And you need to keep bugs and leaves out of the water. Maybe a closed system with a tank would be wiser. Then instead of running the water into the hot tub, you could just run a coil of hot water in the water of the hot tub. Aw, it's getting too complicated. In the future every house will have a large holding tank that'll hold 1000 gallons of water or so as a sink for heat in the summer and a source for warmth in the winter. It will drain directly into the water heater. So just wait until the future and everything will be taken care of.

I have done exactly this about 13 years ago and the system works fine to this day (knock, knock, knock). If you have the capability and skill to silver braze and pressure test some copper tubing, recover the refrigerant, open, and recharge your system, and, of course, want to take on this project, I will be happy to provide more details on my system for you. It involves fabricating a simple heat exchanger that you will install in the high pressure line between the compressor and your current condensing coil. You will have to add some additional refrigerant to your system to make up for the increased system volume after adding the heat exchanger. And, you will be using your current filter pump to circulate the water. I found that no fancy controls were necessary to operate the system and no harm is done to your A/C system if the filter pump isn't running. If you're currently paying to heat the hot tub, every BTU you can "steal" from the A/C system is a BTU you don't have to pay for. Let me know if you would like me to provide additional details by replying to this post. By the way, if you would rather not build the heat exchanger, you can purchase a marine unit that can be plumbed into the system. This, of course, would add considerably to the cost.

1. list principles

2. list materials

3. list quantites

4. either purchase or wait,wait,wait to acquire FOC

1: Insulation, thermal mass, heat transfer

2: Concrete, rock wool, evacuated cellulose sponge and foil composite, aerogel composite. electric pump, copper pipe, underfloor heating pipework

3: <5W leakage, lots of (tons), 100Watts (source)

4: Fill cellar or dig deep

Alternatively, wrap bath in rockwool and put the heatexchanger in over the 23 hour period between baths with the bath full. Remove the heat exchanger before getting into the bath!

My in-laws lived in Florida and had a water cooled AC system that used the pool as a heat exchanger. They had a 2' high frog by the pool that sprayed hot water from its mouth into the pool. I remember on a nice summer day the pool temp was over 105^O. On a hot summer day you may be able to boil your tub dry.

What is the goal?

The form will follow the function.

A hot tub is too warm to allow your a/c to operate efficiently. The a/c will have to work harder, consume more energy in order to provide enough heat. My gut feeling is that heating the water high enough to be usable would consume more extra energy than the exisiting heater in the hot tub. Warming pool water...that would make sense. Warming re-plentishment water...that would work as well.

Also, there is too much electricity and water mixing for MY comfort in most of these ideas. I know, its fine until something goes wrong....

An acquaintance of mine set a "soaker hose" on top of his air conditioner condenser. The a/c loved it, stopped working nearly as hard. Cut his a/c bills by 25%. The condenser rusted out in three years. Jury is still out on whether it saved him bucks in the long run.

In the 1970's some folks were taking the condenser heat from household refrigerators to preheat the water going into their water heaters. Your idea is very similar. It should work fine. The concern about efficiency is a non-starter, because you are adding this ahead of the traditional condenser coil, where the refrigerant temperature is quite high. In hot weather, the condenser coil is exposed to air temperatures frequently over 100deg-F anyway.

Go for it.

JMM