Attic to Pool Heat Exchange, will car radiator collect heat?

[shanngrila]

TL;DR Summary

I want to move Florida attic heat to swimming pool. Will pumping pool water thru a car radiator work?

My attic gets very hot even with the exhaust fan I installed. I would like to move than heat to my swimming pool. I currently have a FAFCO solar pool heater where the pool pump pumps water up onto my roof and thru the 12' long solar panel and down back into the pool. I would like to free up roof space for PV solar panels but still want to heat my pool. Electric pool heater will cost me over $4000 plus electrical cost to put in 50 amp fuse. I could divert the water being pumped to the roof instead into my attic and thru some sort of heat collector to move that heat to the pool. Will a car radiator work in reverse to collect heat from the air? Could be a series of car radiators hooked together. How would a car radiator react to pool water? I would have the collector sit in or above a drain pan just in case. What other problems am I not thinking about? Thanks! Kevin

 

[Baluncore]

Welcome to PF.
Black poly-tubes will exchange heat more reliably and without the need for radiators and fans. So put long tubes inside the roof, into the top of the attic. Continue to pump water to move heat from inside the attic to the pool.

 

[russ_watters]

Yes, a car radiator will work, but you should do some engineering to figure out how well. What is the temperature of the pool? Desired temperature? Attic temperature? Pool volume? And you should be able to look up the specs of a particular radiator and predict its performance at your parameters.

Black poly-tubes will exchange heat more reliably and without the need for radiators and fans. So put long tubes inside the roof, into the top of the attic. Continue to pump water to move heat from inside the attic to the pool.

What do you mean by "reliably"? Given the low thermal conductivity of poly(ethylene), the OP will need a lot, and it will be difficult to predict how much and how it will perform. To me, a radiator is more reliable in that its performance is more predictable (there are other pros/cons).

 

[berkeman]

My attic gets very hot even with the exhaust fan I installed.

Where is the exhaust fan located and how big is it? If it is mounted on the side of the attic, were you planning on putting the radiator up against the exhaust fan to pull the hot air through it?

https://www.nachi.org/attic-ventilation-systems-part1-25.htm

 

[berkeman]

I would like to free up roof space for PV solar panels but still want to heat my pool.

Also, have you checked to see if there are solar panels available that have water cooling to keep their temperature down? If so, you might be able to use the waste heat of the PV panels to still heat your pool. I did some web searching briefly to see if I could find panels with water cooling (fin cooling is common, I guess), but no luck so far. Maybe ask your PV company if they have such panels?

 

[Lnewqban]

I like all above explained good ideas.
Living in Florida and working in attics and swimming in pools for many years, I would suggest going the route of water heating solar panels.

The reasons are that, once the solar load heat enters the attic space, it likes to remain inside there and does not like to go out via any heat exchanger; via radiation transfer, it heats up every possible material and mass that is in the attic, the roof plywood, the trusses, the ductwork, the ceiling insulation, the stored Christmas decoration, carboard boxes, everything.

Unless insulated with sprayed foam, the roof plywood becomes a huge radiator, able to heat up everything up to 120°F or more, since early in the morning, even the hard-to-heat-up air contained in the attic.

Reducing the amount of solar load going inside the attic seems to me that has been a better approach than trying to pulling it out once inside.
The shield effect of solar panels installed directly over the roof greatly help regarding that idea.
If the circulation pump of the pool (or a booster pump) is used, those solar panels could be more efficient.

That will not satisfy all the heat that a swimming pool requires, but it would help reduce the size of a dedicated pool heat pump and simultaneously would reduce the AC related electrical bill.
Windy cloudy days require extra pool heating because heat loss due to evaporation of water from the pool surface, but flat solar panels still work very well in cloudy conditions.

Please, see:
https://www.engineeringtoolbox.com/swimming-pool-heating-d_878.html

https://www.energysage.com/clean-heating-cooling/solar-hot-water/

 

[HeatingGuy]

Summary:: I want to move Florida attic heat to swimming pool. Will pumping pool water thru a car radiator work?

My attic gets very hot even with the exhaust fan I installed. I would like to move than heat to my swimming pool. I currently have a FAFCO solar pool heater where the pool pump pumps water up onto my roof and thru the 12' long solar panel and down back into the pool. I would like to free up roof space for PV solar panels but still want to heat my pool. Electric pool heater will cost me over $4000 plus electrical cost to put in 50 amp fuse. I could divert the water being pumped to the roof instead into my attic and thru some sort of heat collector to move that heat to the pool. Will a car radiator work in reverse to collect heat from the air? Could be a series of car radiators hooked together. How would a car radiator react to pool water? I would have the collector sit in or above a drain pan just in case. What other problems am I not thinking about? Thanks! Kevin

Hello, this is the HeatingGuy...

Yes and no... The chemicals in the pool will break up the copper/aluminum and will end up in the pool and become toxic...I would recommend (well pipe) ... It will survive the winter months and it's strong... I would recommend 1/2" 3/4" to 1" loop in the attic. Maybe enough pipe to hold up to 5 gallons of liquid. One in, one out., 1 circulator pump, 1 thermostat, Honeywell sells a thermostic control, some operate on 12 volts and some work at 120 volts. That all can be in the attic. You will also need a thermostat and a roll of 18/2 wire to run to the pool... There's also a car wash website (sunnyscarwash) they will have most of the items for a very reasonable price... Now if you circulate the pool water? Plastic, stainless ; potable fittings are recommended! That means no heat pex (o2 barrier) or brass pex fittings...
With the annual treatments for the pool these will become toxic and won't last long...

I just had a thought... Depending on the winters and if you want to drain the system every 9 months... 1-1/2 schedule 40 flexible pvc. Is recommended for the chemical treatments... You can also use a pool or spa pump, and the 120 volt Honeywell system...

Another thought... You could also put a coil of water pipe (pex, copper, etc) and loop it to your domestic hot water for your water heater...?

You would just loop that in with; shut off Valves, a bypass, and drain for the cooler months. You wouldn't need a circulator or any controller unless the water gets to hot...?

I hope this will assist you on your journey...

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Thank you for your time and patience,

HeatingGuy