Technology

For the same reason why they let so much water evaporate. They could convert some of that heat back into electricity, just like they could run closed-loop cooking systems, but it would cost more money than it would save. There's no financial incentive to do so....

.... Until regulators start insisting! These datacenter folks have gobs of money, we shouldn't be shy about requiring them to not ruin the local environment.

It would be best to do it on a national level, otherwise these folks will just shift the development to someplace without the regulations.

Turning waste heat into electricity is a very old goal but it really does come up against problems with entropy fast. Basically if you have a LOT of heat in one place you can boil a great deal of water and make electricity. If you have a lot of heat spread over a wide area there’s no good way to “herd” it together enough to boil water in appreciable amounts.

why they’re letting so much heat energy out into the atmosphere

Surely at least some of that heat could be tuned back into electricity.

To harness useful energy from heat, you have to let heat flow from hotter areas to colder areas, to permit entropy to increase.

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

Entropy is central to the second law of thermodynamics, which states that the entropy of an isolated system left to spontaneous evolution cannot decrease with time. As a result, isolated systems evolve toward thermodynamic equilibrium, where the entropy is highest. "High" entropy means that energy is more disordered or dispersed, while "low" entropy means that energy is more ordered or concentrated.

They might be able to harness energy from the flow from warmer to cooler areas, but whether or not they do that, at the end of the day, they have to let the heat go, just like a power plant that uses water-evaporation-assisted cooling. If they're near the ocean, they can maybe stick it into the water instead of the air, and maybe to some degree, you can stick heat into groundwater. But they can't just take a unit of heat and convert it into a unit of useful work and not have that unit of waste heat.

You can, in areas that have a use for heat, make use of that waste heat. For example, district heating can make use of the waste heat from a power plant

you pipe steam or something from the power plant that you want to be cooler to homes that you want to be warmer.

District heating (also known as heat networks) is a system for distributing heat generated in a centralized location through a system of insulated pipes for residential and commercial heating requirements such as space heating and water heating. The heat is often obtained from a cogeneration plant burning fossil fuels or biomass, but heat-only boiler stations, geothermal heating, heat pumps and central solar heating are also used, as well as heat waste from factories and nuclear power electricity generation. District heating plants can provide higher efficiencies and better pollution control than localized boilers. According to some research, district heating with combined heat and power (CHPDH) is the cheapest method of cutting carbon emissions, and has one of the lowest carbon footprints of all fossil generation plants.

If you live somewhere where that works, it's basically "free" heating from an energy standpoint, which is cool. Much of the US isn't well-suited to residential district heating, because we tend to have residences in low-density suburban areas that are pretty spread out and where it's a pain to transport heat around, but we do have some district heating in city cores. Manhattan, which is one area where we do have high density, famously uses steam heating.

Today, Con Edison operates the largest commercial steam system in the world (larger than the next nine combined).[4] The organization within Con Edison responsible for the system's operation, known as Steam Operations, provides steam service to over 1,700 commercial and residential customers in Manhattan from Battery Park to 96th Street uptown on the west side, and 89th Street on the east side of Manhattan. Roughly 27 billion pounds (12,000,000 t) of steam flow through the system every year.

For that to work, you have to actually have some use for that heating (and you probably only want heating some of the year, unless you're up in the polar regions or on a mountain or something).

You can also use waste heat to drive industrial processes that require heat, but waste heat from a datacenter isn't super-hot compared to, say, that from a power plant, so I don't know how interesting that necessarily is. Lots of chemical processes that might require elevating something to a much higher temperature, but a datacenter

at least using current computing hardware

normally tries to keep temperatures from getting to something like the boiling point of water.

Some greenhouses will also use waste heat (in the case of power plants doing cogeneration, some of the waste carbon dioxide as well) to help boost plant growth.

The primary issue is that there's a limit to how much energy you can get out based on the difference in temperature between the cold fluid (liquid or gas) and the hot fluid. With data centres it's maybe 20°C? Based on that assumption and the Carnot Theorem you get a maximum work extraction efficiency of about 6-7%.

Unfortunately, in the data centres they obey the laws of thermodynamics.

It would work better in places that get colder, but unfortunately places like that don't tend to have as much available electricity (or infrastructure).

In less fair weather places you could do district heat. Use a data center to provide heat for a few Condo complexes or something.

There are systems that do heat recovery, but that didn't really help this problem