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Cindi Anderson
Engineer, CPHT
Asked a question 10 months ago

I'm trying to determine what my effective COP would be of a cold climate heat pump in my climate (6B, 8500 degree heating days). Everyone in my town tells me to do NG because our gas is so cheap, but my heat loads are much lower than they are used to, and I don't think they understand the efficiency of heat pumps even in cold climates. (Prelim calcs are about 60MBtu/$350 in heat load and 19MBtu/$112 hot water with NG.) Anyone know of a calculator to help me figure it out, or a good site that would walk me through the steps?

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Tim Eian
CPHD at TE Studio and Climate Action Activist

Cindi,

In our own research and calculations, which were supported by a vendor and PH certifier, we find that cold-climate (outdoor) air-to-air heat pumps (for space heating) in a Passive House in climate zone 6 and around 8,000 heating degree days currently achieve a COP between 2 and 2.5.  

The way to beat low natural gas prices and get away from the CO2 source is to build Passive House, or EnerPHit, then add the heat pump and—very importantly—fuel it with carbon neutral electricity. That way you minimize cost and environmental impact. 

Indoor air-to-water heat pumps (for domestic hot water heating) can achieve higher COPs as they utilize (70º F) indoor air to create hot water (so they steal it from Peter to give it to Paul). Those can be above 3.5.  

The heat pump supplier should provide a table of COP vs outdoor temp, which is what you enter into PHPP. 

Here is a heat pump database you could look at

ASHP (neep.org)47

I would suggest having a mechanical engineer design the system to ensure it works as you hope it will.