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0 pointsLeonard_of_Q16d ago0 comments

That is what you use the heat pumps for, to transform what you call "low-grade heat" to... "higher-grade heat"?

The COP for a heat pump doing such a transformation can be very high, i.e. for a relatively low power input you get a lot of gain.

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mlyle16d ago· 2 in thread

Do the math on pumping 40C water any distance in a loop. It is hard to make it worth it. The water cools off and the pumping takes significant energy, plus the pump and all the piping cost something.

Then using a heat pump on it makes it even worse.

Low grade heat source is not a term I made up- it refers to heat sources under 100C.

Even much hotter low grade heat usually goes unused. You usually need a perfect confluence of a warmer source, very close need for building heat, and a willingness to pay more for environmental friendliness for it all to work out.

Leonard_of_QOP14d ago

Here's an article on the subject of using waste heat from data centres and other sources for district heating. It includes the math you told me to do as well as references to other articles on the specific subject of using "low-grade heat sources" in combination with heat pumps to feed district heating networks.

https://www.sciencedirect.com/science/article/pii/S136403212...

mlyle14d ago

And, again, the economics. The hypothetical Polish project cited in the paper showed a breakeven in 6.1 years... if one ignores time value of money and assumes it is delivered for the estimated cost. The annuity formula tells me that at a reasonable 10% discount rate, payback would be in 10 years. Modest overruns in cost from this naive estimation push that to never.

https://scispace.com/pdf/planning-data-center-waste-heat-re-...

And again this is a pretty idealized case-- very nearby housing, optimistic estimated costs.

Other projects analyzed in your paper had "raw" paybacks of 15 years and 17 years-- AKA never in actuality.

When we are talking about protecting the environment, efficiency and return on capital is important. You'd be better dumping those projects into generating more green energy instead of trying to reclaim the DC energy. This is why:

> > Even much hotter low grade heat usually goes unused. You usually need a perfect confluence of a warmer source, very close need for building heat, and a willingness to pay more for environmental friendliness for it all to work out.

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