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Just over a year ago, we got solar panels and replaced our gas heating and water heating systems with heat pumps for our Boston-area 1938 Cape. (We still have gas kitchen and laundry, waiting for a kitchen refresh in a few years.) This thread is about how that year has gone.
We worked with @MassSave, Byggmeister, and Dolphin Insulation to insulate and air-seal the house. We filled empty wall cavities with cellulose, replaced fiberglass with cellulose to get better sealing, sealed off a vermin-invested crawlspace, and encapsulated our attic.
With 10.4 kW of solar on the roof, by the books we should be nearly net-zero. The HERS rater gave us a rating of 2 – and 47 without the solar. That means we should use less than half of a new code-compliant house (HERS 100), before solar offsets almost all of it.
From June 26, 2019 through June 25, 2020, we used 11,767 kWh and generated 11,372. We also used 39 therms of natural gas (energy equivalent to 1,143 kWh). So, not quite net zero, but net consumption of 1,538 kWh for the full year.
I think dehumidifier use is the difference between actual (where it runs a lot) and the HERS-modeled consumption. Also, we've been at home for four months, instead of at school/work.
The heating and solar don’t line up by seasons, as you can see in this chart of daily production and consumption.
Daily elec. use is very much driven by temperature. Use rises as it gets colder, and rises faster than linearly because the HP efficiency falls off a bit as it gets very cold. Heating energy use is right in line with the specs of the HPs and the @energyvanguard modeled heat load.
We have four separate @MitsubishiHVAC heat pumps, so it’s not possible to separate the heat delivered by unit. However, the basement unit runs nearly nonstop all winter, and the second-floor unit runs the least – which makes sense given that heat rises.
We have an electric resistance backup unit on the 2nd floor ducted system, but it has never run. Only a couple of times last winter, on the coldest mornings, did the HP system fail to hold temperature (and then it would fall only to ~65 before catching up as the sun rose).
Overall, we are pleased – pleased with the quiet and comfort, with the nearly-zero energy costs (especially after the SMART incentives), and with knowing that the largest piece of our GHG emissions has been removed.
