Today (1/3/2012) was an average of 24F from midnight to midnight (eyeball estimate at the historical data charts at wunderground.com and weatherspark.com)** And the eMonitor is saying we used ~22KWh to run the air-source mini-split heat pumps for heating (and also a little help with hot water heating). So that’s approximately 900W average continuous. 24F is pretty close to typical for a Dec day in MA… And if you pay 20 cents/KWh for your “GreenUp” electricity that one can get from National Grid or NStar in MA… Then that’s 0.900KWh * 30 * 24 * $0.20/KWh = $129.60 for heat for the month. That’s the pocketbook.
Now what about from the house’s perspective?
Assuming a COP of maybe 2.5 on the heat pumps during this time, and assuming the weather is not too bad (we had some decent sun today — 27KWh from the PVs — and not too windy) then that’s 2.5*900W = 2250W. That’s a load of a hair dryer and a third to keep the house at 68F on a winter’s day. Glad to be using a heat pump instead. A hair dryer would get a little expensive, though probably still less than many are paying to heat their New England home.
Gotta like lots of insulation and carefully taped external sheathing.
** Note on weather: I do still have my networked “weatherdirect” thermometers tracking temps, but I haven’t set up any logging yet. I really should do that so I can do some useful graphs instead of all this hand-waving with estimates.
- Erik’s weatherdirect setup