swimming pool pump and air source heat pump

[adv]

Hey lads,

so got a swimming pool kids are loving it, however they spent most of last year coming out looking like smurfs, so late on in the year we purchased an air source heat pump rated at 1.9kwh, (pump is another 400w total 2.3kw) works amazing got pool temperature from 20 degrees to 30degrees running it for 12hours a day. however as you could imagine cost started mounting up rapidly.

I wanna know if its possible to run a very basic system no bells or whistles that just powers the air source heat pump during the sunlight hours, obviously such a system i would want it to run for as long as the sun could power it, however any cost reduction is better than none? would it be possible to perhaps charge up multiple car batteries then discharge them on the air source heat pump over a few hours? can i perhaps just buy multiple solar panels and plug them in direct to the air source heat pump? got over 25sqm of roof I can use so plenty of space available. (could 2nd hand solar panels be used for such a system?)

would really appreciate some advise

thanks
Kris

 

[snoobler]

2.3kW of input is going to require much more than that in solar as you'll need to produce that as a minimum. Here's a "traditional" analysis:

12 hr * 2.3kW = 27.6kWh/day - probably doesn't run all the time, but this is the worst case.

It's worth noting that the average American household uses 30kWh/day.

Assuming $0.12/kWh, $3/day, $90/month.

To replace that, you'd need 27.6kWh of batteries (about $4000 for LFP) and about 5-6kW of panels ($2500-3000) depending on sun, quality $3000W inverter - $1000, 100A SCC - $1000, misc $500.

6kW of panels is about 36 sq-m of area... not small.

So, you'll need about $9500 to be able to run it.

You should break even in about 106 months (months of usage, not months from initial purchase - if you only use it 4 months a year, 26 years).

Only want to run for 4 hours per day? Cut it to 1/3.

Have you considered a simple solar based pool heating system? Direct solar heating of water has the potential to be 5X more efficient than PV (20% at best). Powering the pump will probably only be the ~400W or so you currently have running, or it could run off your existing filter pump.

 

[Hedges]

I would suggest much less battery (ideally none.)

If consumption is to be 27.6 kWh/day, you certainly don't need 27.6 kWh of battery. That would only be required if you charged the battery all day without running heat pump, then ran heat pump all night with no sunlight.
Instead, just enough battery to supply starting surge of pump.

2.3 kW of induction motors will draw 5x that starting (just for as second). Inverter needs 12 kW starting surge.
The suggested 3000W inverter may not be sufficient.

Given a small battery, shut off pump when battery reaches low state of charge, restart when charged.

PV panels - These start around $0.30/watt so possibly $1500 to $1800.
Aim half the panels at morning sun, half at afternoon. This will even out production more during the day, so less cycling of battery.

If you are in some jurisdictions of the U.S., rooftop panels may now require "module level rapid shutdown", a feature that turns off high voltage for safety of firemen on the roof. That would add cost. Need to find your local rules, make sure all equipment and the system complies.

The above systems are for battery operated. Do you have utility grid, and can you get "net metering", where you spin the meter backwards for credits, spend the credits at other times?
If so, a grid-tie PV system can be built for $1/watt or less, producing power for $0.05/kWh (amortized over 10 years).
Compared to the notional utility rate of $0.12/kWh, it will break even in 4 years.

Grid tie eliminates batteries and the need for an inverter that can start the motor.

 

[JanLewisfD]

Why do many people choose heat pumps to heat the pool? For me personally, the most important criterion is that they are more effective for a long time. Although heat pumps are more expensive than water heaters, they tend to become more economical over time because they require less energy. That's why I decided to purchase it using a special service. I also hired professionals to install a heater in the pool. Now I am absolutely satisfied with everything. I advise you to do it too. I hope I helped you.

 

[Browneye]

Consider a solar water heater instead. Much more efficient and cost-effective for pool water temps. Simple solar collectors and a small circulation pump. Even some easy DIY options.

Our 27K gl pool has a 200K btu LNG heater - it only runs during spring and fall, or when we want to use the attached spa. And really, now that the kids are gone, it rarely gets used. We've been there thirty years. There's quite a few solar water heaters on roofs in the neighborhood.