Heat Pump Boiler efficiency for hydronic floor heat ?

last year

This is for a 11' x 28' outbuilding (sauna + commons space). They cannot get NG or LP so need to rely on electricity for heat. Primary purpose is to keep keep the space warm enough that pipes don't freeze. Secondary purpose is space heating and warm feet.

Is there an outside temp where a heat pump boiler (1kW = 0-3kW heat?) becomes less efficient than an electric boiler (1kW = 1kW heat?)? Or does it vary quite a bit?

Thanks,

Featured Answer

PRO

Charles Ross Homes

last year

If you look at the weather/climate data for Lincolnville, ME you'll find the average daily minimum temperatures are well above zero F so a cold-climate heat pump would be a good candidate. Here's a link to daily temperature data averaged over the period 1999 to 2019:

https://en.climate-data.org/north-america/united-states-of-america/maine/lincolnville-141391/

"At what point would a Heat Pump not be able to provide sufficient energy?" A heat pump won't be able to provide sufficient heat when conditions are below the system's balance point. That's a function of both outdoor temperature and the sizing of the system vs. the required heat load for the building.

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Comments (7)

Elmer J Fudd
last year
How is it that propane is not available?
fsq4cw
last year
Efficiency of an air source air-to-water (hydronic) HP varies but below a COP of 1 would be below -13˚F or -25˚C in many cases.

Freezing can be prevented with a mixture of antifreeze. Backup generator might be advisable.

Where are you located?

IMPO

SR
opaone thanked fsq4cw
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PRO
Charles Ross Homes
last year
" Efficiency of an air source air-to-water (hydronic) HP varies but below a COP of 1 would be below -13˚F or -25˚C in many cases." I agree. Now, that doesn't mean that a cold-climate heat pump boiler is a bad choice, it just requires you to evaluate the amount of time it would operate with a COP greater than one versus less than one. The heat pump manufacturer may publish data on COP at various temperatures. By comparing those versus climate data for your local climate zone you can make an informed choice. You'll need to calculate a SCOP (seasonal coefficient of performance) which is essentially the weighted average COP for your climate zone based on outdoor temperatures.
opaone thanked Charles Ross Homes
opaone
Original Author
last year
Thank you guys. That's helpful.

In this case the building will be in Lincolnville Maine. Some very quick in-my-head calcs tell me that a heat pump for their hydronic system would be worth it?

Is there need for a backup source? At what point would a Heat Pump not be able to provide sufficient energy?
fsq4cw
last year
What’s there now? What water temperature do the emitters want to see?

Is there a plan to replace or modify the emitters and distribution system?

What’s the capacity of the electrical entrance?

Can you post pictures of the system & mechanical room as it exists now?

IMPO

SR
Kevin Andy
last year
Great question! Heat pump boilers (or air-to-water heat pumps) are generally far more efficient than electric resistance boilers, especially in mild to moderate temperatures. They can deliver 2–3 times the heat per kW used (thanks to COPs of 2–3 or higher), but their efficiency does drop as outdoor temperatures fall—typically below freezing. In really cold climates, a standard electric boiler (which is always 1:1 efficiency) may become more reliable, though it’ll cost more to run overall.

It really comes down to the climate in your area and whether the heat pump has a good low-temperature performance spec. For smaller outbuildings and frost protection, even a modestly efficient system might do the trick with good insulation.

If you're planning a setup like this, we've got resources and equipment options tailored for flexible heating needs:
https://rapidboilerhire.co.uk

Best of luck with your project—it sounds like a great space!
opaone thanked Kevin Andy