3 ms·

Good points, but in case anyone is still reading, I feel compelled to stick to my guns: I think it matters where you are. Figures 7 and 8 in this 2022 paper fr

by nkurz 4y ago

Good points, but in case anyone is still reading, I feel compelled to stick to my guns: I think it matters where you are. Figures 7 and 8 in this 2022 paper from Lawrence Berkeley Lab give maps of the seasonal minimum heat pump COPs necessary to achieve cost and CO2e equivalence with a 95% efficiency gas furnace: https://escholarship.org/content/qt8pt9155c/qt8pt9155c.pdf https://escholarship.org/content/qt8pt9155c/qt8pt9155c.pdf. It requires making some assumptions about heating season air temperatures, but I think it shows that with current electricity generation there are several states where air source heat pumps are actually worse for emissions. And that at current energy prices, there are several states (not necessarily the same) where they are not a win for running costs. Betting on the future "greening of the grid" is a good argument, but the timescale matters. I like the future of heatpumps, but I worry about a backlash if the benefits are oversold.

marssaxman 4y ago
I appreciate your attention to accuracy in this discussion. I think we are basically arguing against different oversimplifications, not really disagreeing about anything fundamental. My own house was built with hydronic floor heating, via natural gas. We added a ductless heat pump a few years ago, but we primarily use it for cooling. It would be a clear win from an environmental perspective, since our utility is 80% hydro and 0% coal/oil/gas; but the radiant floors are so much more comfortable that we haven't made much use of electric heating yet. We'll probably have the heat pump upgraded in a year or two, to cover more of the house; perhaps that'll be a good moment to shift our habits and see how it works out.
- nkurz 4y ago
  They aren't real common, but there do exist air-to-water heat pumps that can be used for radiant floors. They usually aren't hot enough for pre-existing baseboard, but hydronic flooring runs cooler. Not sure about availability, but here are some specs from a Canadian manufacturer: https://www.arcticheatpumps.com/specifications.html https://www.arcticheatpumps.com/specifications.html.

by nkurz 4y ago

marssaxman 4y ago

I appreciate your attention to accuracy in this discussion. I think we are basically arguing against different oversimplifications, not really disagreeing about anything fundamental. My own house was built with hydronic floor heating, via natural gas. We added a ductless heat pump a few years ago, but we primarily use it for cooling. It would be a clear win from an environmental perspective, since our utility is 80% hydro and 0% coal/oil/gas; but the radiant floors are so much more comfortable that we haven't made much use of electric heating yet. We'll probably have the heat pump upgraded in a year or two, to cover more of the house; perhaps that'll be a good moment to shift our habits and see how it works out.

nkurz 4y ago
They aren't real common, but there do exist air-to-water heat pumps that can be used for radiant floors. They usually aren't hot enough for pre-existing baseboard, but hydronic flooring runs cooler. Not sure about availability, but here are some specs from a Canadian manufacturer: https://www.arcticheatpumps.com/specifications.html https://www.arcticheatpumps.com/specifications.html.