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The home heating thing is interesting, since burning gas for that is roughly 100% efficient. Burning gas for electricity maxes out in the best possible case at 60%, and then there's some tranmission loss (though I suppose gas leaks from pipes need to be counted as well then).

But, electric heat pumps don't generate heat but, as the name suggests, "pump" it from one place to another, so they can be more than 100% efficient, generating something like 2-3x the input energy for air source, or up to 5 for ground source pumps. Which puts electrity ahead again (especially as some of that electricty can come from low carbon sources rather than gas).

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Heat pumps only work in mild climates though. From what I understand, you can't heat your home with a heat pump in a place like Wisconsin, where the temperature is below 0F for a fairly substantial part of the winter.

I hadn't even heard of a heat-pump until recently, which makes sense, since they seem to mostly be concentrated in warm, dry areas.

Edit: According to Wikipedia, I'm specifically thinking of Air-source heat-pumps, which have a terrible coefficient of performance below 17 degrees Fahrenheit. Geothermal is better, though I believe you still have problems with saturation in cold climates.

If you don't have natural gas or want to burn wood, basically your only choice is electric resistive heating (COP = 1) or an air source heat pump (COP > 1, above 10-15F) (other options like ground/water source heat pumps are possible but expensive/need specific conditions), the heat pump option will be more efficient, even in a cold place. When it gets cold enough that the heat pump isn't performing you simply turn on the auxiliary resistive heaters instead, there will at least be some days in the shoulder season where the heatpump is beneficial from an efficiency standpoint. If it makes economic sense is another matter. I think if you are going to get central AC or a minisplit its not that much more expensive to get a heatpump.

If you have natural gas it makes sense, economically, to use that to heat most places in the USA.

> you can't heat your home with a heat pump in a place like Wisconsin... Geothermal is better, though I believe you still have problems with saturation in cold climates

Geothermal heat pumps can definitely work in the portions of the upper midwest. I know some people in both MLK and Madison that have heat pumps.

As far as I understand it's hit and miss, though. Depends on the particular piece of property you're living on. And you may need an additional heat source for occasional use (e.g. the super cold winter a couple years back I know one of those folks were super glad they still had gas heating in addition to the heat pump).

> I hadn't even heard of a heat-pump until recently, which makes sense, since they seem to mostly be concentrated in warm, dry areas.

Ironically I'm the other way around. Didn't hear about heat pumps until moving north. Probably because heat pumps don't make as much financial sense in warmer climates where you're not blowing $100+/mo on heat?

My air conditioner in Tampa has a reverser valve to run as a heat pump when it's cold out; it'll run down to 0F using only the air source condenser unit.

My understanding is the limit to the heating potential of a heat pump system is the evaporator freezing over, which is why they are more popular in areas with low humidity. I think at a certain point the heat pumps spend so much time in defrost mode with the auxiliary heater running that they aren't economical.

Wintertime humidity is rarely if ever high enough for frost buildup to be an issue--it's the humid shoulder seasons that have this problem, but your heating/cooling needs during those seasons aren't that high anyway, so defrost cycles won't lower comfort and efficiency all that much.

I think we are talking about two different things. Everyone I know with geothermal heat pumps just call them geothermal. What I have heard called heat pumps are basically air conditioners that can also be used to heat the home.

Until recently I had no idea the air conditioner-like heat pumps existed, and it appears that they are only useful if you live in a place with a low dew point and relatively high minimum temperatures, since they can ice pretty easily and don't work well below a certain temperature.

Anyways, Most of the people I know with geothermal in Wisconsin have fairly large tracts of land, and still need to supplement with wood pellets or something similar. I'm not sure you could fit enough of the heat exchange loops in a typical yard in a densely populated area.

To be honest, the last time I did the math was probably about 10 years ago, but I recall vertical systems are really not cost effective if you have access to a city natural gas system unless you really like AC.

That being said, I'm renting right now, so I haven't kept close tabs on recent developments.

Edit: Also, I think heat pumps are installed in warmer climates because a dual-purpose AC that doesn't heat that well is cheaper than installing a separate fossil fuel based system, which would be overkill as well as much more expensive.

Air source heat pumps have become much more efficient at lower temperatures than they used to be. The best units from Mitsubishi, Fujitsu, Gree, et al, put out their nameplate rating down to -13 to -20F, and continue to produce >50% of their output at COP > 1 below -30F. For new construction, or if you need to replace your current boiler/furnace for some reason, heat pumps always beat gas in levelized cost unless gas is extremely cheap compared to electricity in your area.

> unless you really like AC

Given changes in climate as well as obesity rates, more and more people will really like AC as time goes on, even in the coldest places.

This is a case where building climate-appropriate structures helps tremendously.

Thorstein Chlupp / Riena LLC builds net-zero-energy homes in Fairbanks, AK. He has numerous very long (1-3 hour) videos describing his design methodology and process in detail. The homes are designed, from the sub-grade up, to be as efficient as possibly in a high-heating-need environment. He makes extensive use of thermal mass and insulation, as well as design features minimising heat loss, and maximising gain.

At the core of his homes is a a 5,000 gallon stratified thermal storage tank -- a repurposed fuel tank filled with water, and packed in roughly 1 meter of insulation on all sides. Sourced heat, from solar thermal panels, a wood stove, and other sources, is fed to this. It drives both space and water heat for the structure itself.

Walls have 18"+ insulation, all fittings are thermally isolated, heat exchanges are used on air and water transfers, etc. It's pretty impressive stuff.

For Wisconsin, you might not choose to apply all the concepts, but the idea of banking heat (or chill) in the summer (or winter) through some form of mass storage (ground, tank, other), might apply.

There are community thermal storage systems which have been designed and deployed in both Canada and Germany.

https://en.m.wikipedia.org/wiki/Seasonal_thermal_energy_stor...

http://www.reina-llc.com/

That's pretty sweet. My cousin in-law is actually a builder in Marquette, MI, which is on Lake Superior on the Upper Peninsula.

He talks a lot about similar building concepts. I know he takes a lot of pride in building extremely efficient homes. I think I've listened to him talk about heat exchangers for several hours straight before.

He mentioned they can't do geothermal effectively up there because the bedrock is above the frost line. They have less than a few feet of soil in a lot of places before you get down to granite. I imagine geothermal has issues with permafrost that makes installation similarly difficult.

Thanks for the links, I'll definitely check them out.

That's where some of Chlupp's concepts -- building on top of a very large sand base, for example -- might come in handy. He doesn't make use of geothermal (ground-loop) heat pumps though.

Video search: https://m.youtube.com/results?search_query=thorstein+chlupp

These two in particular detail the design logic:

https://m.youtube.com/watch?v=AtHkvpRI6fc

https://m.youtube.com/watch?v=Xen_VWyDezY

A fair bit of his technology comes from Germany, as does he ;-)

And there are some videos there that run less than an hour. Though I find the two listed to be well worth the time to watch -- information dense. You can skip through bits if necessary.

A minor nit: Burning gas for heating is not 100% efficient, unless you really want to die of carbon monoxide poisoning. Combustion gasses are exhausted to the atmosphere. Heat is transferred via a heat exchanger into the recirculated internal air of the house.

[1] https://en.wikipedia.org/wiki/Central_heating

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