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.
-1F go little buddy!! pic.twitter.com/0HR30GCpjQ
— Mara Abbott (@MaraKAbbott) November 18, 2022
It's a balmy 26F here in VT and our two Mitsubishi MSZ-FH units are doing well as we go into our fourth winter with them. After three winters without using the natural gas furnace we finally had the line disconnected when we got the HPHW a couple months ago. All-in now!
— Kevin Thorley (@kevinthorley) November 18, 2022
We have a Bosch IDS 2.0 running in Boulder, CO…it works!!https://t.co/b6drSAExYo
— Elephant Energy 🐘🔌⚡🔋🏡 (@elephant_energy) November 18, 2022
Mitsu Zuba 24k. We've just dipped in the below 0 celsius (high 20s for US folks) and the house is more consistently warm and with fewer cold spots than w/ gas furnace. We rarely get below -10C here, but I'm looking forward to seeing how the heatpump works when it gets colder.
— Quinn Duffy 🇨🇦 (@QuinnDuffy) November 18, 2022
Looking at this Mitsubishi model – how does it compare to Daikin Fit on cold temp output? “Mitsubishi model PUZ-HA24NHA1 24k BTU/h Hyper Heating Outdoor Heat Pump”
— Dai Ellis (@DaiEllis) November 18, 2022
Very similar, output at 5F is a good thing to compare, it’s in expanded performance charts.
— Nate the House Whisperer (@energysmartwv) November 19, 2022
See this old chart I put together. https://t.co/obI4o9Xn3B
Sent that heat pump nerd’s spreadsheet to my nerd family, who speak fluent HVAC.
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. 😉
(BTW, he is definitely a “controls person” at both the hardware and firmware level.)
so what does “controls” mean for me and my thermostat?
Pretty much the thermostat, the electronics and firmware (built-in software) that decides when to run the system, how early to start heating/cooling to meet a target temperature, etc.
More primitive heating systems (electric ovens, old microwaves) run by bang-bang control, where the device only has ON or OFF modes, so the controller has to do all of the calculating about how often to cycle the device to reach the desired output.
https://www.motioncontroltips.com/wp-content/uploads/2017/10/Motion-controller-FAQ-how-to-address-overshoot.jpg
I probably should have led with this, but I had to get my nerd on, first.
https://www.detmersons.com/three-key-components-of-your-household-heating-system/
19*F and our Fujitsu is keeping nicely warm. Designed for -15*F.
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.