An interesting topic. I would say useful but still simple fields to add to HeatpumpMonitor would be total installed cost after grants, annual operating cost for electric, and estimated previous gas cost. That would let others see what is reasonably achievable, and use as goals for their installations.
I feel a reasonable goal is get the heatpump operating cost close to par with nat gas cost. Even that is a tall order with the low cost of nat gas, at least here in US. We used to spend $280-360 annually with nat-gas heating, and used $380 worth of electric annually with ASHP (one winter).
I’m in South East Michigan. Our house had a 60000 btu/hr input nat gas furnace with high temp (~140-180F design) hydronic fin tube rads, central ducted R22 A/C, and a wood stove in central area of the house. It was cheap to operate, because we didn’t use much A/C and nat.gas (w/ wood stove and keeping rest of house generally very cold).
We have had grid-tied solar since 2011, and in 2020-22 added more solar and battery to work better with new grid tariff, and losing net-metering. Around then, we moved separate water heating & A/C meters onto the main service, and also additional electric consumption with an EV. The outflow credit is still ok, with my electrical system set up to outflow usually only on-peak, and only inflow if needed off-peak. 1 kwh of on-peak outflow gets a credit worth 2-3 kwh of off-peak electricity, and that works very good for EV charging, and heating. For heating, usually the demand for heating is overnight anyway, and the hydronic system has some heat storage that can limp through the peak hours if there is heating demand.
In fall 2022, I tore out the nat-gas furnace boiler, and replaced it with an 85gal plastic lined water heater tank (meant for DHW, but good enough as a buffer tank) and heated only with resistance elements, only with off-peak electricity. Worked fine, we were stingy with the thermostats, and it cost only $360 for the season for the electricity. That’s if we paid $.12/kwh, but it was banked credits, and we did actually not spend anything on nat-gas. Earlier in the year, I replaced the nat-gas range with an induction range, and turned off the nat-gas service. The cost for the heating change was <$1000, with a cheap used tank, new circulator, fittings, etc. We avoid ~$300/yr in nat-gas cost, so that’s very good payback, only because the simple electric resistance boiler was so cheap, only about 3 years. Technically the range was also required to abandon gas, ~$1000, so we spent $2000 to abandon nat-gas to save say $300/yr. Even with that, 7 years is pretty good. That’s not including cost for the PV & batteries which make the electric ‘free’… Payback wise, could’ve stopped there for the best economic payback, but I would like to have more heat, and burn less wood.
In 2023, I installed a split ASHP system which provides A/C to the air handler unit, and provides hydronic heating via a refrigerant to water coil. The outdoor unit is a ‘cold-climate’ GreeFlexx/MideaEVOX MrCool badged R410a w/ EVI, and my rudimentary datalogging measurements for hydronic water flow, delta T & electric consumption indicate SCOP in the low 3’s. It is a 3ton 36000btu/hr capacity, but setting it at 2ton gets better COP. Again DIY, with some used or discount parts, total cost after $2000 tax credit was $5650. It used $380 worth of electricity for the winter. So this payback, ($1000 initial install + $5650) / $300 avoided gas cost is about 22 years!
The green line cCOP is ‘cycle’ COP integrated over each run cycle, and the SCOP is integrated since the little ESP32 has been last reset. The openenergymonitor is very neat, but I made this basic ESP32 meter and use my other existing IOTstack logging with it. Here’s more about the monitor and the DIY ASHP system.
https://www.reddit.com/r/DIYHeatPumps/comments/189mlyy/diy_airtowater_cop_measurement/
This summer, I installed a conventional R410a mini-split in the garage, since it would be nice to take the edge off the worst summer and winter days. We still had some extra banked electricity credit after last winter’s heating season. Hopefully soon, I will get to more improvements to the house hydronic system: replace some fin tube with radiant wall & floor loops to get more emitter capacity at low water temps, add a second 85 gal buffer tank.
