Thinking about adding a heat pump to save on gas heating bills

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Fresnoboy

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Jun 12, 2016
9
San Carlos,ca
Hi everyone. We built a new house up here in the Menlo park CA part of the SF Bay area a couple years ago. It has a 20x50 pool, with a cover, and is heated by a 450,000 BTU gas heater. The family loves to swim year round, and my wife and daughter especially love to swim (she's on a local swim team), but like the temperature at 85-89 degrees. This results in a pretty big gas bill, > $700/month. This is almost certainly driven by the pool, as the house heating is all done by heat pumps, and there is a very high efficiency condensing hot water heater that works extremely well, so I think the pool is most of that.

Our PG&E pricing for electricity is rapacious (0.19/kWH off peak, and 0.51/kWH peak), but they also have been hiking gas prices, and with the push to punish people for using gas, I think it's only going to get worse. Most of our gas usage is in the tier 2 price at $2.41/therm.

We maxed out solar panel installation, and have about 27 kW of generation on the roof of the house, garage and poolhouse, and overall generates about 100 kWH (average over a year) of solar a day. Of course in PG&E land, excess solar gets sold to PGE for $0.03/kWH off peak, and $0.07/kWH peak. So I was thinking that we could reduce our gas heating if we used a solar pool heat pump in addition to the gas heat. We'd keep the spa on gas, but the main pool could be heated offpeak, and especially used during the time when the solar is being generated, as PG&E doesn't pay us much for that energy.

Weather here is pretty mild even in winter, so a heat pump would have pretty good efficiency here. I wish I could have tied it in to the home heatpump systems so that it could heat the pool with the heat being removed during air conditioning, but there aren't really systems that can do that at the residential (ie single phase power) level.

This would be messy from a control POV, as you would want the heat pump to run the bulk of the time, and use the gas heater to boost it when it couldn't close the gap adequately. The pool is controlled by a Pentair Intellicenter system, but I am a software engineer and have a great Home Assistant system integrated, as well as a RpI running the nodejs-poolcontroller package, so I think I can probably make the controls part work.

Would it work to plumb the heat pump in BEFORE the gas heater in series, or would a separate pump etc... be need?

It would be nice to cut back on the gas bill, especially if I can lever some of the "cheap" kWH that are available to heat the pool inside of PGE paying a minimal amount for them.

Has anyone done this before? Am I crazy for thinking about this idea?

thanks!
Mike
 
Mike,

Do you have any room left on your roof that is near south facing? I suggest that because solar thermal panels and a floating bubble cover are a good option in our area. Solar thermal panel efficiency runs in the area of 40 to 45% where the solar electric panels are 14 to 20% efficient.

I'm right next door to you in Redwood City and I have both solar electric and solar thermal panels on the roof for pool heating. The solar panels keep the pool above 90 degrees from about now through the end of October. Last Friday the pool was at 87 degrees from just the solar alone before we had this latest batch of weather. Since the pump runs during the day powered by the excess solar electric generation heating the pool is essentially free for 5 to 6 months of the year. My panels are copper panels made by SunEarth that I installed 30 years ago and they are still working great.

For the cooler months a heat pump isn't going to work very well as its still going to use the same amount of electricity but it's heat output will be way down. They spec the heat pump BTU output at an outside temperature of 80 degrees and it's not going to be anywhere near that in the winter months.

If you have the roof space, or land for solar thermal panels that may be a cheaper and more efficient way to go. Typically you want to have an area of about 75% of the surface area of the pool for the size of the panel array.

Mark
 
Thanks Mark. We had not really thought about the gas prices when we did the build, so the poolhouse has a good amount of panels on it, but they all have 350W LG panels on them. All the usual places that can have solar do, including a terrace with glass panels on top. It would be possible to retrofit them with thermal panels, but I like the electricity being generated.

Thx
mike
 
Grab you a great heat pump and use that solar power up as it is cheaper to use the power than to sell it.. :)

At the end of the year you really want to owe them nothing and them to owe you nothing..

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Problem is the initial heat pump costs. I am guessing around $7500+ for your area. I am not sure you'd ever see an ROI on that. Your electric is sky-high and as you understand, heat pumps run all the time. If you can't swing this for some sort of solar, I don't see this ever saving you any money. Being religious about putting the solar cover on after use will save you a considerable amount of money.
 
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He has 27 KW of Solar power on his roof.. he can easily add the heat pump and not pay any more to the power company as he is generating power locally using solar panels...

@Fresnoboy That is a whole lot of solar.. How close are you to not owing anything to the power company or how much do they owe you at the end of the year?
 
I think a lot depends on the solar agreement he has. If he owns the excess power production I think I'd recommend investing in a PowerWall for nighttime usage of power. Where I live 95% of installations the solar grid is entirely owned by the company that installed it and they get all of the benefits.
 
PoolGate said:
Where I live 95% of installations the solar grid is entirely owned by the company that installed it and they get all of the benefits
Click to expand...
Pretty sure its consumer nature and widespread. Somebody knocks on the door and offers to do it 'for free' and they keep the extra power produced and the homeowner gets 'locked in' to a $250(?) monthly bill.

Of the few who paid for it themselves, most took what equates to a car loan and they pay that each month instead of the electric bill. Depending on the loan terms, it will be 'free power' at some point. Which is kinda sorta true with no more electric bill and the money they would have spent on electricity while paying off the system.

Even fewer just bought the system outright and then pay themselves back with no electric bill and no loan from day 1.
 
I did the second option for my solar.. My solar payment will be 250 bucks a month for 20 years.. While the power company will continue to raise the bill and probably be 600 dollars a month in 20 years.. I will then be on free power :)
 
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cowboycasey said:
I did the second option for my solar
Click to expand...
I had a 'clipboard dude' standing there one day telling me how stupid I would be to buy my own panels. He had 26 reasons from insuring them to replacing them. The costs never add up. Have to remove them when the roof fails. Blah blah blah blah blah blah.

OK. So why are you here begging to put them on my roof. For free. And offering me a lower electric bill to sweeten the pot ? Why are 20 more of you going to come, salivating at the square footage of my roof ? It's so stupid, right ? :ROFLMAO:

Options 2 and 3 are the way to go. But most people hear the free option that lowers their monthly bill some and locks them in forever at that price, and go option 1.
 
Thanks for the comments everyone. Yes, off peak (which ends at 3 PM for me), PGE pays me $0.03/kWH for energy sent means it's basically free to use, though it's complicated to try and control the pump schedules etc.. to use it effectively. Has anyone plumbed a heat pump and gas heater into the same system? How would that be done? The other downside is that the heater wouldn't run for long amounts of time - only when the electricity is basically free. So I need to try and calculate how much gas this would save before seeing if it makes sense.

Also, I have a sta-rite heater, which turns out not to be as efficient as some other models - I think it's 85% efficient, so I am trying to see if it pencils out to upgrade that to a 95% efficient system. Not sure how to do the calcs on that. The equipment is only a couple years old, so it should be awhile before it needs replacing. The pool contractor clearly didn't think about efficiency or saving gas - he just said gas is "cheap", but that was clearly a relative statement! I engineered the electric power systems with a high focus on efficiency, but didn't focus on the pool as much as I should have.

There is an automatic pool cover, but it's a gray color. When it's time to replace them I'll have them put in a black color that will do a better job of heating.

It is a LOT of solar - the structures do lend themselves well to solar panel mounting, and we built a covered terrace that has a bunch of solar glass panels that allow light to shine through between the solar cells, so that helps a bit too, plus higher output LG panels.

The poolhouse does have roof space that I could replace the a few panels with solar thermal panels, and plumb them pretty easily to the pool equipment near by. There are some combo solar PV/thermal panels out there, but for some reason most of the vendors that build them use lame PV cells, with poor efficiency, and some have reported reliability problems. This would seem to be the best of both worlds, but seems like the technology is not there yet. Anyone here using these?

I may be able to reuse the panels if I replace them with a thermal system, but I will need to do some research here on the best kinds.

Any other advice for me?
 
There is nothing cheap about operating a pool. Between extra gas and electric, my pool costs me an additional $500/month (every month not just pool season since I have utility cost averaging). That doesn't even include repair costs and annual chemicals. I just grin and bear it and accept it as the price of family fun. We do not take many vacations so this is like a big annual vacation except it is a staycation instead. :cool:
 
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I wonder if you could do the normal water solar panels under your PV panels you have now... best of both worlds :)

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