Wednesday, 3 February 2021

Trying to quantify KwH of electricity I will end up using if I switch to heat pump

My Current status:
1995 built 3400 sq ft two storeyed home in Bay Area, CA. Home has fairly good insulation. 1500 sq ft has cathedral ceiling. Lots of big and small windows.
Gas Heating , two zone, Downstairs furnace is 110000 BTU and Upstairs furnace is 85000 BTO, was installed in 1995 so 80% efficient.
Furnaces are way oversized as has already been pointed out by a helpful pro member on this forum and he suggested that I may need only 60000 BTU total.

Last year, I used 500 therms of gas to heat the home as reported on my PG&E bill ( deducted gas cooking range and water heater consumption ). My actual heating therm requirement should be 0.8x500 = 400 therms / year or 400*30 = 12000 KwH / year.

Assuming the good heat pumps have COP of 3 in temperate weather that Bay Area has , I guess these pumps should consume 12000/3 = 4000 KwH / year to produce the same heat energy of 400 therms needed to heat my home.

Is this guesstimate correct , at least as a ballpark figure ?

If I replace these two gas furnaces with two ducted heat pump system, the loss of heat due to ducts ( whatever is its state ) becomes a common factor in both systems and so, my guesstimate of 4000 KwH / year still holds true . Is this correct assessment ?

And if I decide to go for ductless heat pump system, the heating need should be lower that 4000 KwH due to gain in efficiency because of elimination of ducts and ability to heat/cool localized area. Is this inference right too ?

Your answers will be of immense help to me as I am planning to install solar and trying to determine size of the system that can handle my future plan of switching to electricity for heating needs.

On a separate note, I was collecting some stats on KwH consumption of MrCool ducted 3 ton heat pump system as reported by people on youtube and noticed that this system is observed to consume 4-4.5 KW when running non stop under extremely cold weather. A ductless 2 ton system is observed to consume 2.5 KW while running under full load continuously. Do these figures look realistic ? Is it reasonable to expect lower KW consumption from better brand manufacturers like Mitsubishi and LG with their true VRF heat pumps.


source https://hvac-talk.com/vbb/showthread.php?2226298-Trying-to-quantify-KwH-of-electricity-I-will-end-up-using-if-I-switch-to-heat-pump&goto=newpost

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