How to run heat pump efficiently - variable electric rates

[BlueWRXPride]

I'm a new pool owner and am trying to figure out the most efficient way to keep my pool heated to around 81. My family typically uses the pool in the afternoons and evenings. I have an Aquacal T115 Heat pump. I also have variable electric use rates, with costs being $0.115/kwh from 7am - 11pm, and $0.032/kwh from 11pm-7am. On the flip side, I know that a heat pump is more efficient when the ambient temperature is higher, during the day. But I haven't been able to find any information as to the power consumption vs BTU output of the heat pump to determine if the better heat pump efficiency out weighs the more expensive electricity.

So far, I've been running my pump and heater from 9pm-7am. I always have the solar cover on the pool when we're not using it. Last night the air temp got down to around 52, and I noticed that when the heat pump came on the pool was at 78, and in the morning at 7am the heat pump was still on and the water was still at 78. So I think it ran all night and just was able to maintain the temperature. Does it seem I'd be better off to flip my schedule and run during the day?

 

[PoolGate]

Heat pump are not "on demand" heaters. They typically need to be set for the temp you want and just allowed to do their thing. That said, 81 is simple to maintain in-season. Your pool should start maintaining this in a week or so with no heater at all. With you liking to swim in cold water I don't see your heater running much. We like to swim in warm water at least 90 so our heater (and costs) are MUCH higher than you would be paying. I can't see you paying more than maybe $50/month to maintain 81. I am at close to $500 in gas to put it in perspective.

 

[BlueWRXPride]

Yeah I appreciate that a heat pump is best left to maintain a temperature. But the heat pump only runs when my pool pump is running, which I currently do 10 hrs a day. So I'm trying to determine if my energy use would be lower by having those 10 hrs be at night, or during the day.

 

[PoolGate]

Yeah I appreciate that a heat pump is best left to maintain a temperature. But the heat pump only runs when my pool pump is running, which I currently do 10 hrs a day. So I'm trying to determine if my energy use would be lower by having those 10 hrs be at night, or during the day.

Heat pumps are useless when ambient temps are below 60. Barely useful in the 60s. But they will use the same amount of power trying to do something. My suggestion is base your usage on temps, which means run during the day.

 

[cowboycasey]

Wow, they got you.. The power hours for us are below.. They are telling you we are going to charge you crazzzzzy rates all day and when no one uses energy at night we will drop your rate... that is really nice of them... Go back on the regular rates and run your heater how you want... I will not be part of that here and it is only 5 hours during the afternoon.. Those 5 hours would cost 90% of my bill here in OK, trying to cool the house when it is 118 degrees outside takes some power...

A heat pump is really great at keeping a set temp, meaning you need to run it 24/7 and it will keep the temp you want, it will turn on and off as needed to keep the temp... If you want to use your heater run the pump 24/7 also...

https://www.psoklahoma.com/lib/docs/ratesandtariffs/Oklahoma/PSO%20Residential%20Service%20April%202019.pdf

The On-Peak Season is the Company's billing months of June through October, inclusive. The OnPeak Hours are 2:00 pm to 7:00 pm, Monday through Friday during the On-Peak Season.

 

[BlueWRXPride]

Well, I also have an electric car, so being able to charge that at night for next to nothing has worked out pretty well with the variable rates. In the months when the pool is open, it might be more economical for me to go back to standard rates, but since the pool is only open for around 5 months, it's probably still better to stay variable since it still benefits me in the winter.

 

[BlueWRXPride]

You do have an interesting point about running the pump 24/7 so the heat pump can do what it wants. My pump is variable speed, so I could just find the minimum speed that lets the heater turn on, and run it at that speed for 14 hrs/day, and then run it a bit faster for 10 hrs/day if it seems the slower speed isn't cleaning enough of the water.

 

[cowboycasey]

I think the speed you need for the heat pump should keep the pool very clean.. I moved my VS pump up to 12 hours a day at 1400 rpm now. it does a great job compared to running at 850 rpm I was running... I think you will see the heat pump runs most of the time during the night and maybe some before noon.. it may take a couple days to get to the temp you want then it just turns on and off as it needs..

 

[BlueWRXPride]

But you're still running it 12 hrs a day and not 24, meaning the heat pump can't really do as it pleases. Or maybe I'm missing something.

 

[cowboycasey]

But you're still running it 12 hrs a day and not 24, meaning the heat pump can't really do as it pleases. Or maybe I'm missing something.

I do not have a heat pump I just have a way oversized SWG so no need to run 24/7... I was just throwing out what I do for my setup, sorry about the confusion... I will have to start running at night here in a couple weeks when my water gets over 90 degrees on its own.. Last week it was at 86 to 88 degrees but a cold front came through this week and dropped the temp to 82..

 

[BlueWRXPride]

So back to my initial question. I found on Aquacal's website where it states that 80/80/63 (water temp, air temp, humidity), it puts out 106,000 BTUs. At 80/50/63, it puts out 74,000 BTUs, or about 30% less. I assume that under those two scenarios, the heat pump would draw however much power for both situations. My peak electricity is around $0.115/kwh, and off peak is around $0.032/kwh, or about 72% less. Obviously there are some major assumptions here, but if I assume day temp is 80, and the night temp is 50, all else constant it seems that the cheaper off-peak electricity is more significant than the higher efficiency of the heat pump during the day. Is that a valid analysis at all?

 

[PoolGate]

So back to my initial question. I found on Aquacal's website where it states that 80/80/63 (water temp, air temp, humidity), it puts out 106,000 BTUs. At 80/50/63, it puts out 74,000 BTUs, or about 30% less. I assume that under those two scenarios, the heat pump would draw however much power for both situations. My peak electricity is around $0.115/kwh, and off peak is around $0.032/kwh, or about 72% less. Obviously there are some major assumptions here, but if I assume day temp is 80, and the night temp is 50, all else constant it seems that the cheaper off-peak electricity is more significant than the higher efficiency of the heat pump during the day. Is that a valid analysis at all?

How much did you pay for your pool? Your electric rates are chump change compared to what other's pay. Your high rate is a lot lower than my rate. If you want to swim in a heated pool there is a cost associated with doing that. Nickel and diming your happiness for the few months you get to swim is counter-productive. You are complaining over less than $100/month for 5 months.

 

[BlueWRXPride]

I'm not doing it necessarily out of a desire to squeeze every penny. I'm just a technically minded person who likes to run things efficiently. It costs what it costs, and I'll pay what I need to enjoy the pool. But I just like to have a solid understanding of how to best run my system and do it most efficiently.

 

[PoolGate]

I'm not doing it necessarily out of a desire to squeeze every penny. I'm just a technically minded person who likes to run things efficiently. It costs what it costs, and I'll pay what I need to enjoy the pool. But I just like to have a solid understanding of how to best run my system and do it most efficiently.

You don't have an "on-demand" heater. You have a "run all the time" heater. Heat pumps create enough heat when running to get to and maintain your temperature over time. During a warm day they increase and maintain and during the night, they maintain. If you shut them off during the day, you won't get enough heat to maintain your desired temperature. If you shut them off at night, you'll lose temperature which may or may not be able to be regained during the day. If you are religious about putting on a solar cover at night/when the pool is not in use, you might get away with less usage. But you still should keep it on at its set point it'll just not to to run as often with the solar cover keeping existing heat in. Your best bet is to pick the temp you want, set and forget the heat pump and let it do its thing. And, be resigned that you will be paying $100/month or so in electric during the swim season. I burn through $300-$500/month during the season in natural gas charges. It is part of the joy of being a pool owner!

 

[jseyfert3]

I found on Aquacal's website where it states that 80/80/63 (water temp, air temp, humidity), it puts out 106,000 BTUs. At 80/50/63, it puts out 74,000 BTUs, or about 30% less. I assume that under those two scenarios, the heat pump would draw however much power for both situations.

That’s correct. The power draw is essentially constant, what varies is the heat output which depends on the difference between air and water temps.

My peak electricity is around $0.115/kwh, and off peak is around $0.032/kwh, or about 72% less.

Wow that’s really low. Do those prices include distribution costs per kWh too or just the pure electric rate? The basic residential rate here is about $0.12/kWh for all per kWh charges.

 

[jseyfert3]

You ever heard of the FPH HotSpot? Being a technically minded person who likes things run efficiently it may be up your alley. It adds a water cooled condenser to your home AC, and if your pool calls for heat it redirects the refrigerant from the air cooled condenser to the water cooled condenser.

I’m thinking of getting it, currently our pool is warm enough to get in but not as warm as we’d like, but we’ve been running our AC for months. Be great to reclaim that waste heat and dump it in our pool.

 

[PoolGate]

You ever heard of the FPH HotSpot? Being a technically minded person who likes things run efficiently it may be up your alley. It adds a water cooled condenser to your home AC, and if your pool calls for heat it redirects the refrigerant from the air cooled condenser to the water cooled condenser.

I’m thinking of getting it, currently our pool is warm enough to get in but not as warm as we’d like, but we’ve been running our AC for months. Be great to reclaim that waste heat and dump it in our pool.

There is a recent thread on this somewhere.

 

[BlueWRXPride]

You don't have an "on-demand" heater. You have a "run all the time" heater. Heat pumps create enough heat when running to get to and maintain your temperature over time. During a warm day they increase and maintain and during the night, they maintain. If you shut them off during the day, you won't get enough heat to maintain your desired temperature. If you shut them off at night, you'll lose temperature which may or may not be able to be regained during the day. If you are religious about putting on a solar cover at night/when the pool is not in use, you might get away with less usage. But you still should keep it on at its set point it'll just not to to run as often with the solar cover keeping existing heat in. Your best bet is to pick the temp you want, set and forget the heat pump and let it do its thing. And, be resigned that you will be paying $100/month or so in electric during the swim season. I burn through $300-$500/month during the season in natural gas charges. It is part of the joy of being a pool owner!

Yeah, I'm certainly familiar with that. My house has a geothermal system, so it's the same way in that it can't heat/cool fast, so it's best to leave it constant, and not raise/lower it when you are home or at work for example. I suppose that perhaps it just means that I should run my pump 24/7 at the lowest RPMs that provides the heat pump enough GPM to operate. Then like you're saying the heat pump will do whatever it needs to do.

That’s correct. The power draw is essentially constant, what varies is the heat output which depends on the difference between air and water temps.


Wow that’s really low. Do those prices include distribution costs per kWh too or just the pure electric rate? The basic residential rate here is about $0.12/kWh for all per kWh charges.

Yes, that's distribution and the electricity rate.

You ever heard of the FPH HotSpot? Being a technically minded person who likes things run efficiently it may be up your alley. It adds a water cooled condenser to your home AC, and if your pool calls for heat it redirects the refrigerant from the air cooled condenser to the water cooled condenser.

I’m thinking of getting it, currently our pool is warm enough to get in but not as warm as we’d like, but we’ve been running our AC for months. Be great to reclaim that waste heat and dump it in our pool.

Interesting. When we were planning for the pool, I had asked about the ability to tie in our pool to our home's existing geothermal system. I was told that doesn't really work, one reason being that the pool could only be heated when the home's AC is running, which probably wouldn't work out. That HotSpot FPH looks pretty cool, but doesn't look like it's compatible with my geothermal system. Very cool though.