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Originally Posted by GoofBall

Let's assume it gets as bad as some have suggested: Isn't it still more efficient to heat exchange with 100F water than with 80F air?

The COP (efficiency) depends on the "lift" - the temperature difference between indoors and outdoors. If you want 75F indoors: 80F outdoors requires only 5R(Rankin) of lift. But 100F outdoors requires 25R of lift, with a corresponding drop in efficiency.

This answer has been bugging me: If you have a perfectly efficient exchange with an 80F sink of course you prefer that to a 100F sink for cooling. But isn't a sink's thermal conductivity a factor in residential heat pumps? Or is every air-cooled compressor in typical working condition able to get the refrigerant to the ambient air temperature using the exterior fan and heat exchanger?

Originally Posted by BigBlock

Old post but I thought I'd put some numbers to the question....

Assume the hp is rejecting 3 tons of heat into a medium sized inground pool of 20,000 gallons.

Heat into pool 36,000 btu/hr
Specific heat of water 1 Btu/lbm-°F
Pool water volume 20,000 gal (167,000 lbs)

=167,000 lbs / (36,000 btu/hr / 1 Btu/lbm-°F)
=4.63 hrs/°F

Actually, a 36000 BTU unit will have to reject at least 15000BTU per ton or total 45000BTU/h for 3 tons including superheat etc. So in a 8 hour day of running AC you would get somewhere around 360,000BTU, which is equal to about 7 of the extra large solar water heating panels from somewhere like aquatherm. That's enough to maintain heat in most pools. There are some products on the market that heat pools with air conditioners, not sure if they work with heat pumps. Google hotspot pool heater to see an example.

Waste Heat From House To Swimming Pool

I built a system such as the one that is in question here and it is in its sixth year of operation. The WSHP is a Climate Master 5 ton that was designed/intended for geothermal application. The only water the WSHP has ever seen is the water from a 18x36x6 vinyl ig pool, location being Long Island,NY.

I am a professional pool builder by trade, not HVAC. The system works flawlessly and is part of a pool system that creates more energy than it consumes. ( No this is not over-unity nonsense), but relies on the fact that the pool is idle for 5 months of the year.

Should anyone need free advice on how to heat your pool for free, do not hesitate to contact me.

To OP - Not to over-simplify, but wouldn't it cheaper and simpler - if you are just trying to cool a relatively small space for a couple hours at a time - to install a small ductless AC or, heck, even window units? I'm not a tech but this whole pool setup seems like overkill!!

Originally Posted by BigBlock

Old post but I thought I'd put some numbers to the question....

Assume the hp is rejecting 3 tons of heat into a medium sized inground pool of 20,000 gallons.

Heat into pool 36,000 btu/hr
Specific heat of water 1 Btu/lbm-°F
Pool water volume 20,000 gal (167,000 lbs)

=167,000 lbs / (36,000 btu/hr / 1 Btu/lbm-°F)
=4.63 hrs/°F

So for about every 4.6 hrs of run time on the heat pump, the pool water temp would increase 1 degree.

This is assuming no other heat transfer to the air/ground/eveaporation/solar which there obviously will be. During the summer months I think it is safe to say that the pool temp would hit the 100F mark without much trouble after a couple of weeks. I live in upstate NY and even without the solar cover my inground pool maintains 80F+ during july and august (especially this summer). From a more practicle point of view, any pool warmer than 85 starts to feel like bathwater to me.

But it won't evaporation is pretty significant and the warmer the water is, the higher the evaporation rate. Plus it will reject more heat into the ground as well. But yes, it would raise the pool temp. 5-7F wouldn't suprise me. I don't think that's enough heat to hold much over 90F. But it might make the pool less enjoyable mid-summer.

The whole concept is reffered to as a " geo battery " and all the math I have seen on operateing it, the pool/or burried tank is allways followed by how much btu replenishment of the battery in fresh water in and hot or cold water is needed opposed to hours of operation for the heat pump. The one that was built and works was a coil of copper pipe put into a tank that was fed continuously by a natural spring at a slow rate and then piped to waste in the nearby creek. It enjoys being a closed, open loop/ with continuous replenishment. I think the load was around 3 tons or so.
Eric

Old post but I thought I'd put some numbers to the question....

Assume the hp is rejecting 3 tons of heat into a medium sized inground pool of 20,000 gallons.

Heat into pool 36,000 btu/hr
Specific heat of water 1 Btu/lbm-°F
Pool water volume 20,000 gal (167,000 lbs)

=167,000 lbs / (36,000 btu/hr / 1 Btu/lbm-°F)
=4.63 hrs/°F

So for about every 4.6 hrs of run time on the heat pump, the pool water temp would increase 1 degree.

This is assuming no other heat transfer to the air/ground/eveaporation/solar which there obviously will be. During the summer months I think it is safe to say that the pool temp would hit the 100F mark without much trouble after a couple of weeks. I live in upstate NY and even without the solar cover my inground pool maintains 80F+ during july and august (especially this summer). From a more practicle point of view, any pool warmer than 85 starts to feel like bathwater to me.

Originally Posted by GoofBall

I assume your question is "what happens when you turn off the pool waterpump?"
In my proposal the original condensor is still installed and ready for action - just flick on the power switch to the condensor fan, and you're back to the original old-fashioned low-efficiency setup.

lol...you must work for or rep a geo company.

The addition of a condenser fan does not make a AC unit low effeciency. Plenty of high seer air source units that are far cheaper to install and much more practical in some parts of the Country.

It reminds me of the guys that push heat pumps in my neck of the woods when natuaral gas is practically given away.

Originally Posted by GoofBall

Excuse my ignorance, can you explain a desuperheater? I googled, but all I found was a rudimentary/obvious setup for injecting cold water into a steam line.

A desuperheater takes the hi temp, hi pressure gas directly from the compressor and uses the heat to (typically) heat domestic hot water in a commercial refrigeration rack system. As the water temp is generally 140F or more, the refrigerant does not condense, just lose superheat and increase the efficiency of the condenser. Win-win all the way round. In a pool application the refrigerant would condense and do so at a lower temp than an air side condenser. Might even have to worry about too low of a head pressure!

Grocery stores with a meat department tend to use a lot of hot water and this is essentially free heat from the refrigeration and A/C system, so you will generally see a desuperheater water tank there.

Nordyne was selling a system for residential installations a few years back that did the same thing on a smaller scale. Some of the GSHP manufacturers like Water Furnace offer this an an option as well.

Found a link for you at: http://www.energysavers.gov/your_hom.../mytopic=12840

and the paragraph follows:

Homeowners primarily install geothermal heat pumps—which draw heat from the ground during the winter and from the indoor air during the summer—for heating and cooling their homes. For water heating, you can add a desuperheater to a geothermal heat pump system. A desuperheater is a small, auxiliary heat exchanger that uses superheated gases from the heat pump's compressor to heat water. This hot water then circulates through a pipe to the home's storage water heater tank.

Hope this helps!

Chlorine and copper at the levels used in a pool do not mix. It will undergo slow corrosion... meaning those thin wall tubes won't last long.

A pond or stream would work.

Originally Posted by Juan Madera

Add a desuperheater between the compressor and condenser on the gas side of an air-to-air HP or A/C, and let it dump heat into the pool when the circ pump is running.

Excuse my ignorance, can you explain a desuperheater? I googled, but all I found was a rudimentary/obvious setup for injecting cold water into a steam line.

Originally Posted by commtech77

What if you happens when you have to respray the thing ? Or just clean the bottom ?

I assume your question is "what happens when you turn off the pool waterpump?"
In my proposal the original condensor is still installed and ready for action - just flick on the power switch to the condensor fan, and you're back to the original old-fashioned low-efficiency setup.

Has anyone actually witnessed a residential pool-sourced A/C overheat an average 16x32x8' pool? I have no facts, but I just can't see it happening - too many square feet of dissipation area, and too few kW injected into the pool. Plus you guys in the hottest driest Arizona desert have the most evaporative cooling effect.

Maybe you guys are Olympic-Michael-Phelps-types and any pool over 68F is too bloody hot....

Add a desuperheater between the compressor and condenser on the gas side of an air-to-air HP or A/C, and let it dump heat into the pool when the circ pump is running. Nice in cooler climates, but in desert southwest may overheat the pool, so a way to bypass if high temps are reached might be a necessity.

Man what Geo guys wont do to find a water source.

No in ground, above ground pool, septic system, bird bath or muddy puddle is safe.

Sooner or later someone's going to run a stick of copper through it and yell " EFFECIENCY " !

I was thinking about the pool side of the experiment. We have a lot down here in Houston.

They can go south quick AND everyone is installing salt now anyway. What if you happens when you have to respray the thing ? Or just clean the bottom ?

Quote:
Let's assume it gets as bad as some have suggested: Isn't it still more efficient to heat exchange with 100F water than with 80F air?

Originally Posted by beenthere

No, its not.

Aye, the COP (efficiency) depends on the "lift" - the temperature difference between indoors and outdoors. If you want 75F indoors: 80F outdoors requires only 5R(Rankin) of lift. But 100F outdoors requires 25R of lift, with a corresponding drop in efficiency.

Let's assume it gets as bad as some have suggested: Isn't it still more efficient to heat exchange with 100F water than with 80F air?

No, its not.

Originally Posted by motoguy128

I'm pretty sure you don't want to mix copper with pool chemicals.

This is a fresh-water (not salt) pool. Yes, there will be green copper problems if the pH gets too low (acidic), but only if the pool is neglected and falls far from the proper pH range. Other than that, what is the issue? Does chlorine attack copper?

Originally Posted by motoguy128

I'd use a standard water source heatpump, but have a closed water loop to a stainless steel heat exchanger designed for pool water use. Make sure you get the pump sized correctly for the required flow rate on the heat pump.

Alas, buying a new heatpump is not in the budget

Originally Posted by motoguy128

The only problem is that water temps will get into the 80's in the summer on the pool. Your effciency and capacity will be reduced a little by late summer.

In the middle of the day the air temperature will often far exceed 90F, and heatpumps don't complain about that. So using 80F poolwater instead of 90F air will help the heatpump's COP, right at the time when the AC is on the most.

Originally Posted by motoguy128

The energy required to operate the pool feature for added evaporative cooling will consume a fair amount of electricity.

Like I said, I'm pretty sure overheating the pool is not in the cards for my climate.
And like dbooksta says, the waterpump is gonna be running anyway; if aeration is needed, you can build a nice waterfall or something into your pool.

3 Tons of AC: produces about 13kW of heat output.
200,000BTU pool heater: produces about 58kW. (4.5x more).
Obviously neither the AC nor the pool heater will have 100% duty cycle.

Originally Posted by motoguy128

The only problem is that water temps will get into the 80's in the summer on the pool. Your effciency and capacity will be reduced a little by late summer.

Let's assume it gets as bad as some have suggested: Isn't it still more efficient to heat exchange with 100F water than with 80F air?

Originally Posted by motoguy128

The energy required to operate the pool feature for added evaporative cooling will consume a fair amount of electricity.

The "evaporative feature" can just be a redirect of the filter pump returns to spray water through the air instead of under the surface. Pools have to run that pump for hours a day regardless of how it discharges.