zlacker

> It won't stay -21C for very long, if you pump heat into it.

You are right, and also it would require digging which is a lot harder than laying out panels on the surface. Back of the napkin it's a tossup depending on the conductivity of lunar sub-surface material and how much pipe you lay. Just like on Earth.

> Btw, you can make your radiative cooling a lot more efficient than you gave in your example

This is true too, heat pumps could even get higher radiator temps than 100C if you like.

>>foxyv+(OP)
> This is true too, heat pumps could even get higher radiator temps than 100C if you like.

I'm not sure that actually works out to your advantage, because the heat pumps themselves produce extra heat. But I haven't done the math on that.

>>eru+od2
Heat pumps are typically 200-400% efficient. That is, they move 2-4x as much heat as they produce to move that heat. Although that is usually radiating energy to a fairly warm atmosphere. If they are pumping into an extremely cold environment you will get insane efficiencies since you are 'going with the flow' with regards to entropy increase.