I want my pool to hit 90 degrees all the time -- commercial heater needed?

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arizonapoolperson

0
Jan 24, 2018
1
Peoria, AZ
Bought a new house recently, and I am looking for a creative solution. I thought this would be an easy thing to find, but it has turned out to be quite mind boggling...

I have a small residential play pool and built in hot tub. It has a waterslide and waterfall and is a very nice setup for the family. I am in Phoenix, AZ.

We are adding a large Solar Photovoltaic system to our house that will generate a LOT of electricity. We want to remove the old propane pool heater, and replace it with a really nice electric pool heating system. 100% electric, so we can use all this great renewable electricity that we are generating.

We want to heat the pool to a nice warm 90 all the time. We want to heat the built-in hot tub to 102 too.... We want to maintain that temperature 24/7 and 365, even in December in Phoenix, AZ. Every electric residential heat pump that I have seen cannot do that.

I have determined that the residential Heat Pumps that most folks use are just too weak to accomplish what I want. They are fine for people on a budget, but I am looking to burn some electricity and get my water hot!

I've had about 4 companies come out and tell me that it can't be done. They say that what I am asking for just cannot be done with a 100% electric system. They tell me to keep burning propane. But the thing is... I don't want to do that. I want to use all this wonderful FREE electricity that I am generating and enjoy my pool to the max.

It's getting the point that I am getting really frustrated. I think most of the bids are coming from residential specialists who are used to the standard Phoenix, AZ attitude that pools are only for the hot months (June July August), and that people just like to look at them for window dressing in December and January. We actually want to use ours in December and January and enjoy them year round.

I am not operating on any kind of a budget with these companies I never threw out a number. Nobody has been able to provide a solution. I thought it was going to be as easy as writing a check for a company and an electrician to come install a big heater.

Is there a system that can produce 100% of my heat using electricity to get the pool to 90 and hot tub to 102?? Do I need to contact a commercial company? Does anybody else have this problem in Phoenix, Texas, or any other warm place?

Any help would be great. Am I the only dude who wants to heat his pool up to 90, and be able to jump on in whenever he wants?
 
I'm in Australia, so probably not much help. We are about to build and will be installing one of these in the link. It has the highest cop I've come across and more than able to heat to 28* without cover or 30* with cover year round. Our estimated power usage for this is around $800/year at .25c per kWh. Perhaps you can see if this product is available there. It's made in China, so would think it would just be rebadged for each country's distributor. Our pool will be small, but they can have a huge range to suit all sizes. Just thought I'd share so you know it's doable.
 
How big is a BIG solar system (kW)?

The biggest residential heat pump from AES, the company linked above, can put out 24 kW of heating power with an input of 9 kW at 15 °C air temp, or approximately your average winter temp, which is 82,000 Btu/hr in US terms. The gas heater I most commonly see here is roughly 400,000 Btu/hr input, or somewhere north of 320,000 Btu/hr heating capacity depending on efficiency, so you're looking at 1/4 the heating capacity of a "normal" gas heater.

So now you have a small pool heater drinking 9 kW of power, and 9 kW is a really, really BIG solar installation for a residential setting.

I'm not familiar with pool heating, just numbers (engineer), but my gut feeling is that you'd be much better off with a solar water heater for the pool and a smaller PV solar system for your house/pool pump.
 
I don't know what you consider a "large" solar array is and I'm not sure what you consider a 'lot' of electricity, but an electric heat pump system to keep your pool at 90ºF in the winter is going to require hundreds of kW.

Besides looking at commercial systems, you could also look at paralleling two or three large residential heat pumps. Since you don't say anything about the equipment or if you're willing to change out the plumbing, I'm not sure how much flow you can get through a heating system.

You could also entertain adding a large solar water heating system to assist a heat pump.
 
Coates Heater - Pool/Spa
You're going to need 24 kw to match a 100,000 btu per hour gas heater (assuming 83% efficiency).

How much power will be available?

How many gallons are the pool and spa?

I would recommend separate equipment for the pool and spa, not shared equipment. Also, get full automation.
 
Do solar pool heaters work when the temperature outside is cold?

What you want is an electric resistance style pool heater. Highly inefficient and needs lots of power but if you have power to burn, they may be what you are looking for.

Coates Pool Heaters
 
We've had a few nights here in Gilbert (Phoenix area) where there was frost on the car windows, it was cloudy and windy for several days and the sun was at its worst potential for solar collection (winter). You need to tell us the pool size, the PV array capacity and if you are willing to use pool covers or such to reduce the heat loss at night. In my opinion, solar or no solar, you'll need a massive electric heater(s) if you want to keep the water at 90 degrees, 24 hours a day. I don't know of anyone around here who does that outdoors with electric unless it is a small covered spa. Natural gas is the choice for what you want to do. I'm guessing you have no natural gas access in your area? I have excess PV solar production from my 6.63kW system during the winter but I would never choose electric to heat my 12,000 gallon play pool.

Honestly, the PV array figures very little into this question. It's going to be expensive and then some in my opinion.
 
PoolGate said:
Do solar pool heaters work when the temperature outside is cold?

What you want is an electric resistance style pool heater. Highly inefficient and needs lots of power but if you have power to burn, they may be what you are looking for.

Coates Pool Heaters
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I assume someone makes one that would, maybe not. You can get domestic solar water heaters that will get you hot water for your house and work below freezing when it's sunny out.

Electric resistive is definitely NOT what he needs. Cheap, and could be used to burn off "excess" power but at that point it would be way better to not have the extra solar panels. The savings would run a gas heater for quite a few years.
 

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jseyfert3 said:
I assume someone makes one that would, maybe not. You can get domestic solar water heaters that will get you hot water for your house and work below freezing when it's sunny out.

Electric resistive is definitely NOT what he needs. Cheap, and could be used to burn off "excess" power but at that point it would be way better to not have the extra solar panels. The savings would run a gas heater for quite a few years.
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I think electric resistance style pool heaters are actually the only thing that meet his criteria. If you wanted to heat a pool to 90 year round with only electric, what other choice is there?
 
Paul hit the nail on the head. A LARGE ground source heat pump system could likely do what he wants. That would mean multiple deep well bores drilled on the site tho. I you want electrically driven heat that's the only thing that is going to come close in the winter.
 
Besides, why would you want to waste all that electricity into barely being able to heat your pool? Can't you sell the excess your PVs make back to the electric company? Use the proceeds to heat your pool a more efficient way in the winter.
 
PoolGate said:
I think electric resistance style pool heaters are actually the only thing that meet his criteria. If you wanted to heat a pool to 90 year round with only electric, what other choice is there?
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Air source heat pump would work fine for winter in Peoria, AZ. The average winter temp is around 15 °C which is where the specs on the one I mentioned above. Direct solar heat should work too.

Resistive heat and solar = garbage. Solar panels are 17-20% efficient in an array, and since resistive heat is "100%" efficient you get overall efficiency of 17-20%. With direct solar heating you should be able to get 80-90% efficiency, so you're talking 4-5 times more heat for a given surface area and lots cheaper cause it's not PV panels but glass and metal. With an air source heat pump at 15 °C ambient you might get up to a COP of 6 which means if you get 20 Watts of power from your solar panel it'll put 120 Watts of heat into the pool, or an overall efficiency of roughly 120%. So now you are beating direct solar heating by ~50% but at an enormous cost increase in equipment cost.

  • PV + resistive = 20% efficiency
  • PV + air source heat = 120% efficiency
  • Direct solar heat = 80-90% efficiency, and dirt cheap compared to PV panels and heat pumps
  • PV + ground source heat pump ("geothermal") = maybe slightly better than the air source heat pump but way more expensive

Bottom line: PV + pool heat = does not compute. ;)

Oh, and by efficiency I'm talking available solar energy per square foot over energy delivered to pool.
 
So, I've one small consideration to add to the mix.

I do keep my pool between 90-95 degrees year round in Michigan with a natural gas heater rated at 266 BTU. The heater is indoors in the pool house, and in winter the pool is enclosed in an air dome.

The question OP feces is not what will run the temp up to 90 in a winter session. If the pool is actually MAINTAINED to 90, the question is what will it take in winter to recover the daily incremental heat loss.

In the realm of natural gas, my 24,000 gallons x approx 8 lbs per gallons means I need approximately 200,000 btu an hour to gain 1 degree.

But using a cover, I don't lose 1 degree an hour. With the heater off on even sub-zero days I don't lose more than say .4 degrees per hour. On "normal" winter days, eg in the teens, I lose maybe .3 degrees an hour.

So, with the heat pump, one question might be formula-wise with unlimited available energy, will the output keep up with the rate of loss?

So multiply gallons by weight for a rough Calc on btu needed per hour per degree, then divide by 2 or 3 and you should get what you'd need to maintain temp IF Covered.

Of course, that also depends on what temp the heat pump can operate at. For example, my mini split heat pump in my shop operates down to -15 F (Fujitsu.) If there is a pool heat pump than can similarly operate in low temps, then the OP may be able to maintain heat even if underrated per hour, because he will not likely loose a whole degree an hour ;)
 
Maybe consider a heat pump with a gas heater backup.

The heat pump should be able to do most of the year with minimal gas usage.

Check with the heat pump manufacturer to make sure that the heat pump will meet your needs.
 
jseyfert3 said:
Air source heat pump would work fine for winter in Peoria, AZ. The average winter temp is around 15 °C which is where the specs on the one I mentioned above. Direct solar heat should work too.

Resistive heat and solar = garbage. Solar panels are 17-20% efficient in an array, and since resistive heat is "100%" efficient you get overall efficiency of 17-20%. With direct solar heating you should be able to get 80-90% efficiency, so you're talking 4-5 times more heat for a given surface area and lots cheaper cause it's not PV panels but glass and metal. With an air source heat pump at 15 °C ambient you might get up to a COP of 6 which means if you get 20 Watts of power from your solar panel it'll put 120 Watts of heat into the pool, or an overall efficiency of roughly 120%. So now you are beating direct solar heating by ~50% but at an enormous cost increase in equipment cost.

  • PV + resistive = 20% efficiency
  • PV + air source heat = 120% efficiency
  • Direct solar heat = 80-90% efficiency, and dirt cheap compared to PV panels and heat pumps
  • PV + ground source heat pump ("geothermal") = maybe slightly better than the air source heat pump but way more expensive

Bottom line: PV + pool heat = does not compute. ;)

Oh, and by efficiency I'm talking available solar energy per square foot over energy delivered to pool.
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Perhaps it is the contract writer/consultant in me but I keep going back to the requirements. Per his requirements, I think only a resistance heater will work for him. And that may not, but it has the best chance to meet the requirements.
 
Resistance heating is the most inefficient form of heating a pool, by far. We use solar heat for primary heat source and a heat pump for those extra few degrees when it is cloudy or cold. We have no difficulty maintaining 89-92 degree water temp using an undersized solar set up, heat pump and solar cover. Cost is negligible, as in we didn't notice an increase in our electric bill swimming from mid-march to late October in a heated pool. We also use the solar panels to cool the pool in July and August as needed.
 
arizonapoolperson said:
We actually want to use ours in December and January and enjoy them year round.
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While I can understand keeping the spa up in the 100's, you really want to swim here in the winter time? I've swam a few times here at some of the resort pools that are heated but it was generally a miserable experience since the air temperature is not warm enough and there's no humidity. This winter has been unseasonably warm and I can only think of a handful of days where it would have been warm enough to want to get in the pool if the water temp was high. I guess my point/question is, do you really want to keep the water temp at 90* all the time or be able to raise the temp to that when it's going to be 80* here (like this weekend :D)
 
Going off 200k btu heater to heat a pool, which is 58 kw, so to do this correctly you will need:

Massive pv bank, 120 kw or more
Massive charge controller, probably 12 of them or a industrial unit $$$$$$$
I'm not gonna run the numbers for batteries, but a lot, like are you in real estate, is this a lot?
I would also go with a 80 kw generator backup for cloudy days to reduce amount of batteries needed.

This setup should only run in the neighborhood of.......

$120,000 pv panels
$24,000 charge control
Idk batteries
$10,000 genset
 

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