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Comment by cogman10 | Hacker News Reader

What do you mean by efficient?

The heat emitted by the electronics will always be emitted and needs to go somewhere. If 1MWh of that heat is dumped into district heating how would that be less efficient than the 1MWh being dumped in the atmosphere to (hopefully) be reclaimed by a heat pump elsewhere?

Or, alternatively, that 1MWh could be absorbed by the already existing datacenter AC coils which could ultimately still be used to heat up district water as it cools the refrigerant. (People actually do this with swimming pools, using the coils from their AC to heat the pool).

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istjohn is right. Using a heat pump instead of resistive heating (which is basically what a data centre is) is many times more efficient.

That doesn't mean we shouldn't use the heat a data centre provides. It just means that it is not a good idea to neglect the development of energy-saving technology because the heat produced can be used somewhere else.

the issue is that there is an upper limit to how much heat can be removed from a system each cycle, so even if you have a way to disperse the removed heat in a useful way you still can't grow compute beyond a certain point. And because scaling is exponential even immersing the whole rack into liquid nitrogen would only buy a few years of computing growth post-Moore's law.

istjohn is not right. Energy produced by datacenters is simply wasted. even if you will use heatpumps there is still only so much the can produce; using datacenters waste energy would lessen the the power neede for her pumps.

Your point is valid, but that's not really what we were talking about.

You said that using data centre heat is an alternative to reversible computing. This is not the case. Neglecting efficiency improvements and instead moving the data centre to a place where the heat can be used is worse than making it more efficient and using heat pumps with the saved energy at a much higher efficiency. It is even worse if the heat is dumped into the air, as istjohn said.

Also using the heat to heat homes would be even better. The two concepts aren't mutually exclusive.

How exactly is using what is essentially free energy worse than using heatpumps? You will build datacenters anyway; it _will_ happen, irrespective of using or not using heatpumps. Using 10Mw of energy from a DS would mean that you'd need 2.5Mw less of energy for heatpumping.

We're going round in circles because you're just responding to points I didn't actually make. Please read my comments carefully before replying.

Resistive heating generates heat: thus, it cannot generate more than 100% of the energy put into the resistor, because of conservation of energy.

In contrast, heat pumps move heat, so they can move more than the energy put into them. Even cold air (around freezing) has a lot of heat in it to siphon off.

If you're going to run 1MWh worth of compute anyway, then selling the waste heat is still a good idea. But if you weren't, a heat pump will get you more heat energy than a bank of computers with the same energy budget.

But you _will_ build datacenters, this was my point.

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