Coldplay: Hot Thread on Sub-Freezing Heat Pumps

November 18, 2022

I’m looking at having to replace my ducted gas furnace and AC in the next few years, so have been following news about air source heat pumps, which are now reaching high levels of efficiency, even in cold climates.


6 Responses to “Coldplay: Hot Thread on Sub-Freezing Heat Pumps”

  1. rhymeswithgoalie Says:

    Sent that heat pump nerd’s spreadsheet to my nerd family, who speak fluent HVAC.

    • rhymeswithgoalie Says:

      Bro’s response:

      Whatever the relative efficiencies of one heat pump to another, IMHO – this is one leg of a 3-legged stool. The other two legs are quality of installation, and the control(s). After overseeing the replacement of 6 heat pump systems at a previous church, I have become mostly brand agnostic and focus on the quality of installation.

      As a “controls person”, I think I have that leg of the stool covered. ๐Ÿ˜‰

      (BTW, he is definitely a “controls person” at both the hardware and firmware level.)

  2. renewableguy Says:

    19*F and our Fujitsu is keeping nicely warm. Designed for -15*F.

  3. John Oneill Says:

    I’ve been using heat pumps for years, though the temperature here rarely drops much below freezing in winter, and doesn’t get high enough (yet!) to need aircon in summer. The friend who installed my first one, though, has really turned against them, because of the strong greenhouse effect of the refrigerants. (He’s a refrigeration engineer, who has also built about a half dozen electric car conversions, and installed a couple of wind turbines and an array of solar panels at his house.)
    I’ve heard of HVAC systems using CO2 as the refrigerant. This, of course, has a global warming index of one, versus often hundreds for some of the Montreal Protocol-compliant formulations. It’s also cheap, doesn’t need special disposal, and is non-flammable. The problem is, it has to run at very high pressure, over a thousand psi, to reach the supercritical state. On the plus side, supercritical CO2 has very high heat capacity, so the whole system can be very compact. S-CO2 turbines about the size of your forearm can do the same job as steam turbines the size of a small car, and do it more efficiently. The Department of Energy has been funding research for solar thermal power plants, nuclear reactor developers are interested, and there is a gas turbine plant in Texas that burns natural gas in pure oxygen mixed with S-CO2, to provide a waste stream ready for sequestration, plus pure water.

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