Pool heat pumps?

[SajgZi]

Anyone using pool heat pumps to either heat water for heating house or cooling water to spit out hot air in the house? The prices on some of these are pretty low for a water-air heat pump.

Example (there are many in the $600-$1000 range for nominal nameplate heat output):

https://www.amazon.com/villastar-Inground-Heaters-gallons-Electric/dp/B0CGQSBTP7/

Claims up to 4.45x COP but that's for extremely advantageous conditions.

Settable to heat water from 59F-104F (meaning rejecting cool air). Settable to cool water (meaning rejecting hot air) from 46F-82F. In heat mode, outside air range from 23F-109F. The advised flow rate is pretty high (600-1000 GPH) compared to traditional ground source heat pump systems.

Cost: $599. Minimal reviews

Where I am in CO, the ground temp I believe is just over the cool water minimum, which means it wouldn't work directly with the unit inside blowing hot air and the pipes connecting to coils of plastic pipe buried in the yard.

I can think of a few ways to "assist" the heat pump to get going but all require extra energy input (sun, warm ambient, etc). It might also be possible to rip out the provided controller and do a DIY one to get some low temp run time going. Of course the COP would plummet. But getting COP of even 1.5 is better than resistive heating during cold snaps.

 

[Hedges]

I have a house with gas central furnace and gas water heater.
Will be putting in 15kW PV, under NEM 2.0 for 20 years.

The downstairs is not conditioned, although it gets some heat from equipment in the utility room. The appliances take combustion air from the room, which has a vent screen from basement. I'm considering boxing them in with air baffles so it doesn't suck house air, but keeping some duct work to radiate heat.

What I wanted to do was add HPWH in cold water line prior to gas water heater. Set it for higher temperature, and turn on during off-peak rates. If grid down, turn on when battery full. Gas water heater would kick in only if temperature drops. Then plumb a loop to baseboard radiators to heat downstairs. Maybe to a radiator in the furnace air handler. Put tempering valve after gas water heater so domestic water temperature is not increased.

Objective is to use my DIY kWh that cost $0.025 instead of gas, but have gas as fallback.

An air to water heatpump such as you show could be used, would need its own circulator pump to heat water when not heating house. But 104F isn't enough, want about 140F or more.

I would guess HPWH have different refrigerant or charge pressure, to operate at desired temperatures. Actually, I'd expect radiator side of an AC to be well above 104F, which isn't even hot weather. With reverse-flow heat exchanger, ought to work well both as heater and as A/C.

 

[newbostonconst]

I have a Geocool water to water that I use in the summer to take heat our of our "heated floors" and put in our hot water tank....Many use mini splits....

 

[OzSolar]

From experience I can offer that 104f water isn't going to add much heat to the air in a water to air application. Both air hot water coils and baseboard radiators are rated at 180f or higher incoming water. Some publish specs for lower temps but the BTU output is dramatic. It's worse than linear if I recall correctly so unless you could reconfigure the controller to raise the water temp the pool heat pump by itself won't do much for your air.

Have you bumped into Artic Heat Pumps? Last I checked they started at $4k but they do claim to work down to -22f. I REALLY wanted to go this direction to back up my radiant in floor/wood boiler application but it was just crazy for no more often then I'd use it in my cooling dominated climate.

Since I'm grid tied and normally take a few hundred dollars of credits into December I instead went with a water heater that I converted to allow both elements to run at the same time. 11 kW has had no problem gobbling up all my excess credits and then some these last 6 weeks.

Air to Water Heat Pump Specifications for Cold Weather - Arctic Heat Pumps

Explore the specifications and details of Cold Climate Heat Pumps. Learn about the model's features, accessories, price and more.

www.arcticheatpumps.com

 

[Partimewages]

From experience I can offer that 104f water isn't going to add much heat to the air in a water to air application. Both air hot water coils and baseboard radiators are rated at 180f or higher incoming water.

This is old thinking/Engineering. Many in floor and radiant systems don't use over 120F now.

Pool heaters are notoriously poor quality units and generally lack efficiency.

 

[OzSolar]

This is old thinking/Engineering. Many in floor and radiant systems don't use over 120F now.

Pool heaters are notoriously poor quality units and generally lack efficiency.

My comment was "104f water isn't going to add much heat to the air in a water to air application"

OP mentioned "water to spit out hot air in the house" so I assumed the OP was thinking about a hot water coil, like people with wood boilers use in forced air applications.

I once knew a little about radiant. I've done few dozen radiant systems from design to install but it's been a while. Even 20 years ago most high mass radiant in floor systems could get away with 90f or lower. Low mass, particularly a staple up with carpet flooring, could need as much as 130f IIRC.

 

[hwy17]

Get a heat pump designed for your application. They make them for heating domestic water and homes.

A pool heat pump will be optimized for heating pools of course. They are very crude compared to the other kinds. They only run a very specific delta usually at one speed.

 

[Warpspeed]

I suppose a lot depends upon your location and climate.
Where I am, the cost of a heat pump, even a cheap crappy one would buy a huge number of used solar panels.
A direct electrically heated water pre heater with a constant solar voltage (mppt) controller then becomes really simple.

 

[Quattrohead]

Who is looking for YouTube video ideas? Haha

 

[ruralsolar]

My comment was "104f water isn't going to add much heat to the air in a water to air application"

Lookup john siegenthaler on youtube, he's been pushing low temp hydronics for a long time.

I heated my house through winter with A2W heat pump with a max water temp of 101, at 32F I only need 97F water. This is for radiant in basement concrete slab and an air handler for the rest of the house via existing forced air ductwork.

 

[OzSolar]

Lookup john siegenthaler on youtube, he's been pushing low temp hydronics for a long time.

I heated my house through winter with A2W heat pump with a max water temp of 101, at 32F I only need 97F water. This is for radiant in basement concrete slab and an air handler for the rest of the house via existing forced air ductwork.

I'm semi-familiar with him, even met him at a trade show ~20 years ago. Doesn't mean I know anything though.

At 15F and below I'm able to get away with upper 80's in my slabs. My staple up zones need at least 100f but 110f works best. At 32f my house doesn't need any supplemental heat thanks to passive solar.

I've trained under several folks that spent extensive time in his classes. None of them would ever sign off on sending the same water temp to a slab and a air handler. Any chance you could provide me a link to the YouTube video that has John S. detailing this?

A data sheet on the heat exchanger you've got in you ductwork would be great to see as well.

 

[ruralsolar]

I've trained under several folks that spent extensive time in his classes. None of them would ever sign off on sending the same water temp to a slab and a air handler. Any chance you could provide me a link to the YouTube video that has John S. detailing this?

My brother expressed this too, but he also uses a combo of heat pump and boiler. For John I can't recall an exact video for in-slab and fan coil using the same temp water, he does highlight the design of staple up radiant like you mentioned. The webinars are so long that I'm not going to go looking to see if he mentioned in-slab on the same loop as fan coils, I agree with you that I don't think he did suggest it. I'll say that for me it's working quite well, I don't have a boiler for backup and I also don't have a buffer tank.

I have a Firstco 12MB (spec sheet easily found online) with the A-Coil only, using this derate sheet from Chiltrix. https://www.chiltrix.com/documents/Firstco-derate.pdf . The 12MB at 180EWT has a minimum output of 83900 BTUs, assuming 68F EAT and 100EWT my 12MB "should" be outputting ~24,364 BTUs. The calculated J-Load for our house (built 2021) at -6F and excluding our basement load is 21,396, with the basement it is 33423. My duct work is "run of the mill" ductwork designed for a furnace, fiber duct board mostly.

I have an in-floor slab temp sensor, using an equation from Johns webinars and knowing approximate BTU load for the basement, I know what floor temp the slab should be to maintain a certain air temp. I try to adjust it here and there with the changing seasons. The water from the heat pump is set to adjust based on outdoor temps which doesn't affect slab temp which is a downfall, I'm working with a crew to develop a outdoor reset temp control to adjust the floor temp set-point given the last 12 hour average of the outdoor temps.