Cold Climate household Heat Pump (not a mini split)

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Minister of Fire
Jan 19, 2019
SE North Carolina
The footnote on the table says that defrost losses are not included.

While it would be nice to include them (from a design point of view) the defrost losses vary wildly with the outdoor dew point, precipitation and wind. Maybe some minimum loss is included?

Also, my installer always set up the unit to defrost every 30 run minutes. This was cray-cray. I moved the jumper to defrost every 60 minutes, and cut the defrost losses in half, and reduced the wear on the reversing valve at the same time.
Can’t we just have an ice sensor??


Minister of Fire
Jan 27, 2008
Can’t we just have an ice sensor??

While this seems logical... it needs to be VERY reliable. Bc if it ever fails, then the coil freezes up hard and the compressor can be permanently damaged. In practice, a stupid run-timer is perfectly reliable. And if the coil is dry, the amount of BTUs needed to heat it to say, 40°F (stopping the defrost cycle) is quite small, by virtue of its small thermal mass. So the COP gain we get with demand defrost is maybe 10% or less. Not nothing, but not worth risking the entire system if the 'frost sensor' dies.


Minister of Fire
Sep 18, 2019
Grande Prairie, Alberta, Canada
Have your gas prices dropped like they have down here??


Did a quick look at average electricity price predictions. Looks like they might see a slight increase next year or two then hold flat for a decade then drop by a bit by 2040. At any rate there does not seem to be much predicted change. In the nation averages

Yes, both natural gas and gasoline prices have dropped. Natural gas is about $4/mmbtu (spot price) right now, gasoline $1.29/liter.

For natural gas I assume $10/GJ or about $9/mmbtu for rough math. Half of which is just distribution fees and carbon tax.