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Comment by chess_buster | Hacker News Reader

Additionally Sektorenkopplung (the electrification of Heating and Transportation), will reduce the need for primary energy.

For example, a heatpump can produce 5MW of heating from 1MW of electricity by concentrating the heat from the environment. An electric car is 90% efficient while a combustion vehicle is about 30% efficient, roughly speaking.

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> For example, a heatpump can produce 5MW of heating from 1MW of electricity by concentrating the heat from the environment.

Don't those struggle in cold climates (e.g. winters consistently below freezing)?

> An electric car is 90% efficient while a combustion vehicle is about 30% efficient

On the other hand, even the best batteries have far less energy density than a gallon of gasoline, and some of that "waste" heat can be put to good use (e.g. heating in cold climates).

Yes, the colder the air is, the less efficient a heat pump is. My 10 year old heat pump has a COP of 3 but shuts off at -15C because below that it's less efficient than an electric baseboard heater. Newer air-to-air heat pumps have a COP of 4 or higher so they can handle down to -20C or -25C.

I keep my EBBs set to come on a few degrees below where I keep the house so they will kick in when the heat pump shuts off and they kick out when the heat pump comes back on. This tends to happen at night when I don't mind the house getting a bit cooler anyway. Where I live in Canada, the heat pump typically only shuts off half a dozen nights in the second half of January. It's not like my heat pump is useless 6 or 8 months of the year.

There are also geothermal heat pumps that push/pull heat to/from water from underground (eg. a well, a pond, or a buried coil of pipe) where, even in the winter, the ground remains warm. These don't suffer a loss in efficiency in the winter.

Regarding EVs, most EVs get between 3 and 4 miles/kWh. The Porsche Taycan gets only 2 miles/kWh. The Tesla Model 3 gets 5 miles/kWh. The Aptera gets 10 miles/kWh, which with the 100 kWh battery, gives you 1,000 miles of range.

Fully Charged Show - Aptera (time-indexed to efficiency discussion): https://youtu.be/mpiH-Y-HOvE?t=135

> For example, a heatpump can produce 5MW of heating from 1MW of electricity by concentrating the heat from the environment.

This does not sound right. Can you elaborate that further?

"With 1 kWh of electricity, they can transfer 3 to 6 kWh of thermal energy into a building."

https://en.wikipedia.org/wiki/Heat_pump

Coefficient of power of 3 to 6.

Nit: COP is "coefficient of performance [not power]"

Thanks.

Heat pumps use energy to _move_ heat, not create it. Your refrigerator, for example, moves heat from inside the fridge to outside the fridge. Your AC operates on the same principle. Pump the refrigerant in the other direction (note: mechanically this isn't possible in garden variety ACs) and you reverse the effect. Given the same amount of energy and typical conditions - this won't work to absurdly cold temperatures - it's several times more efficient to use it to run a heat pump than to convert it to heat directly.

They start to lose efficiency roughly around freezing, so not very cold, and can cease working entirely at zero Fahrenheit or so. But geothermal can work much longer because you dig holes deep enough to use the ambient earth temperature instead of air.

This won't work in permanently frozen areas like Antarctica.

I'm always amazed at how in the US there are "garden variety ACs" that lack the very small amount of parts needed to be reversible. I haven't seen any models like that for sale in Europe. Since having AC is also much more frequent in the US than in Europe it's really a shame that isn't just regulated as mandatory or something so that electrifying house heating becomes that much easier.

This also leads to the counterintuitive notion that it’s more efficient to burn natural gas to spin a turbine, and create electricity used to run a heat pump, than it is to burn that same natural gas directly for heat. It’s one of those situations that just shouldn’t make sense, until you do the math and see that it does (although only for ambient temperatures above a certain threshold.)

Sounds weird right? But it really is true: heat pumps pump heat, from one place to another, like a fridge and airco etc. Current heat pumps for home heating use can pump about 3-5 units of energy from outside to inside while the pump requires 1 unit of energy to run.

Trick (to understand maybe?) is to not convert the energy from chemical to heat, but to take existing heat energy and pump that around.

Peltier elements have a efficiency of about 30% of converting temperature differences back to electricity. So if a heat pump pumps 5 times of the energy it needs around, you only need 20% of that converted back to electricity for it to be a self-sustainable perpetuum mobile. Of course this is impossible, but where is the error?

I think Peltier modules or other thermo-electric generators only have <10% efficiency, not 30%.

A heat pump takes heat produced elsewhere (eg in air outside). If that stops or it gets too cold, the heat pump stops working. It's not a perpetuum mobile because it needs an external energy source (eg. the sun to warm the air)

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