Heating spa with vapor compression cycle?

[Stealth20]

I know this probably isn't ideal at all but how effective do you think it would be to use a condenser heat exchanger between refrigerant and spa water? Let's say for example just to keep the temperature of the spa at a constant 102 F.

 

[gruntguru]

That is not unusual. It is called a heat pump.

je suis charlie

 

[georgeverghese]

Thermodynamically, this is possible. But there are tiny details that may make you think more :

a)Spa water isnt exactly non corrosive or sterile - so all sorts of vegetation and bugs will grow on your condensor tubes surface - and you cannnot add biocides to this water.

b)Unless you use completely corrosion resistant materials for the tubes, there is a potential for tube rupture - what if this refrigerant got into the spa water ? Tube to tube sheet joint failures are also commonplace.

 

[MortenA]

@greg, i think your are exaggerating a little. Air to water heat pumps (or water to water or soil are quite common. Just dont take a standard air/air model - Panasonic has some "stock solutions". Couldnt quite find it on the US web pages, but heres the UK:

http://www.aircon.panasonic.eu/GB_en/ranges/aquarea/

This model is intended for heat water for home heating - say that you already have a boiler (oil or propane) but wish to switch to a heat pump. So its not quite what you asked for (and perhaps too high a duty) but its the same concept.

 

[StoneCold]

Stealth20
I think you have to figure out how much heat your air conditioner can give off to get you to 102F. Googleing around a little bit makes me think your discharge temperature on the air conditioner might only be 120F. If that is superheated then you won't get much heat off of an exchanger if you want to keep the water at 102F. You might be able to get the air conditioner to heat up the tub somewhere close to 95F and then boost it from there with propane or electric. You need to do the math on this and see if it is worth all the trouble. A friend of mine has a hot tub and he tells me it costs him about $10 extra a month in Colorado to keep the tub at 104F. Seem like a modification is not worth it.

Regards
StoneCold