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Comment by adrianN | Hacker News Reader

You probably want to install heat pumps instead of resistive heaters. Then you get 3-5J of heat for every Joule of electricity. Retrofitting those into a house with gas heating is quite expensive, so not using fossil fuels for new construction in the first place is probably the right decision.

In Berkeley you can probably slap a small number of solar panels on the roof to produce more electricity than you need for heating (and cooling).

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Do you have actual numbers for the COP factor for modern heating and cooling solutions? If its actually 5 (after accounting for transmission losses from power plant to building and other inefficiencies), then that means electric heat pump heating releases 3x less C02 than a in-building gas heater [1]. A solar panel solution will release like 4.5x (assuming 90% efficiency) less C02.

Finally, burning natural gas inputs additional heat energy into our atmosphere, with the gas-burner inputting 3x more heat into our atmosphere compared to the electric heat pump. A solar panel solution doesn't add more heat to the atmosphere. It takes energy that was going to get absorbed by the atmosphere anyway and concentrates it inside a building for localized heating. Except for the second hand effect of some of sunlight that would have reflected off from the roof back into space, now being dispersed as high entropy heat into the atmosphere.

Not to mention that if you use solar

[1] This is assuming that the power plant is a hybrid natural gas one (60% max efficiency) so 5*0.6 = 3. And the in-building natural gas heater is 100% efficient.

A COP of 5 is quite optimistic for a domestic scale heat pump, at least in the climate where I work (UK). Sensible values here would be more like 2 - 3.5 depending on the temperature gradient required.

This is a function of how big the radiators are and how cold the heat reservoir is, so if you plug an air->water device into some normal radiators its performance won't be good on a really cold day, whereas if you plug a ground->water or water->water device into underfloor heating it'll probably be pretty good.

The big question (in the UK) for per-dwelling heat pumps is whether the distribution network has enough capacity to meet the winter peak load - if everyone gets a heat pump the cost might have to include replacing a lot of substations and distribution wires.

I am interested in the question of whether you could have PV cells on your roof with a coolant loop that goes into a heat pump, and a thermal store in the house for buffering. Then when it's sunny you can dump some electrical heat into your thermal store whilst also use your heat pump to chill the PV cells, keeping them at high efficiency. When it's not sunny you can draw off your thermal store giving a high efficiency for the pump.

If the numbers came out right you might be able to be self-sufficient for heat using something like this, just by making good use of the radiation already falling on the house.

Wikipedia has some numbers:

https://en.wikipedia.org/wiki/Geothermal_heat_pump#Thermal_e...

https://en.wikipedia.org/wiki/Air-source_heat_pumps#Efficien...

These numbers don't account for transmission losses or power plant inefficiencies. But even if you low ball things you likely save some CO2 over just burning the gas for heat, e.g. take the power plant and transmission efficiency to be about 0.4 and even with a poor heatpump efficiency of 2.5 you break even. Not to mention that the heatpump runs on renewable energy without further investment once the power grid is modernized.

It really isn't very expensive. Installation is mostly connecting the inside unit with the outside unit through an 8-10mm pipe (1/3"). The work is about 2-3 hours and material costs are pretty insignificant. The HX units are pretty costly, though. About $2K for a decent one.

Where I live, Norway, a lot of houses have gotten these retrofitted.

Oh that's interesting. What I've heard is that changing the heating system from radiators that use water heated by gas (as is common in German gas heating systems) to a heat pump is difficult because heat pumps don't give you such high temperatures. So you'd need a lot more surface area to heat adequately with the lower temperatures provided by your heat pump, i.e. you'd need to switch to underfloor heating, which means ripping open all your floors. Glad to hear that there are apparently simpler ways. We need to switch almost all buildings over to heat pumps over the next two or three decades after all.

AFAIK it's not ideal but possible to use existing radiators.

My parents recently added an air heatpump to their existing (wood) heating system without changing radiators. They Installed a new boiler (water tank, not sure about the translation) where the top half is heated by the heat pump and they can optionally heat the whole tank using the old wood heater.

In dense enough areas you can also do well with heat distribution networks, or mixed heat and cold networks. These are a good low-regret choice because you have a big central plant which you can easily refit if the best supply technology changes.

Also if you're running a heat pump having one big central heat pump with a big thermal store can allow you to get better conversion ratio from electricity to heat.

In nearby Concord, yes. Have you been to Berkeley?

I love the sense of class humor in Berkeley weather. Down in the affordable flats, the fog often clears. Up in the "four bridge view" hills, not so often. Annual sun striking the entire roof would still generate more electricity than needed, but there's that storage problem.

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