Recycling data center waste heat to warm nearby homes

HostThink about how hot your phone gets when you have too many apps open or you play a game for a long time. Now, try to picture a building the size of a giant warehouse filled with thousands of computers all running at the same speed day and night. We usually spend a huge amount of money and power just trying to blow that heat out of the building so the machines don't melt. But lately, people are asking why we treat all that warmth like trash when we could be using it to keep our own feet warm. How do we actually take that heat from a computer chip and get it into a person's living room?

GuestIt really starts with a change in how we think about what a computer is. We used to think of them as just machines for math, but they're also very good at making heat. In a big data center, you have rows and rows of these computers called servers. They drink up power and spit out hot air. For a long time, the plan was just to use giant fans to push that hot air out through the roof. But air isn't very good at holding onto heat. If you want to move that warmth to a house down the block, blowing air through a pipe isn't going to work. It cools down way too fast. To solve this, engineers are starting to swap those fans for liquid. They run cool water through tiny pipes that sit right against the hot parts of the computer. Water is amazing at grabbing heat and holding onto it. By the time that water leaves the back of the computer, it's nice and warm.

HostI have to stop you there because water and computers seem like a terrible mix. One leak and you have a very expensive mess on your hands. Is that really safe?

GuestIt does sound like a disaster, but the water is kept in a totally sealed loop. It never touches the actual wires or the chips. Think of it like the radiator in your car. The engine gets hot, the metal around it gets hot, and the water flowing through that metal carries the heat away to the front of the car. It's the same thing here. We use a metal plate that sits on the chip like a sandwich. The water flows through the middle of the sandwich and sucks up the heat. It's actually much safer and more quiet than having thousands of fans spinning at top speed. Plus, because the water is so much better at moving the heat, we can pack the computers closer together. We can fit more power into a smaller space.

HostOkay, so you have this warm water leaving the building. But "warm" for a computer isn't necessarily "hot" enough for a person. I don't think a lukewarm shower is what people are looking for in the middle of winter.

GuestThat's a fair point. The water coming off a computer might be around ninety or a hundred degrees. That's fine for a bath, maybe, but it's not hot enough to run the heaters in an old apartment building. Those systems often need water that's closer to one hundred and fifty degrees to really work. This is where a bit of clever gear called a heat pump comes in. You can think of a heat pump like a fridge running in reverse. A fridge takes heat out of your milk and pushes it out into your kitchen. A heat pump takes that lukewarm water from the data center and squeezes the heat out of it. By squeezing it, it makes a smaller amount of water much, much hotter.

HostBut that sounds like we're just using even more power to fix a problem we made ourselves. If we have to run these big pumps to make the heat useful, does it actually save any energy in the end?

GuestIt actually saves a ton. If you wanted to heat a house with a normal electric heater, you have to turn all that power into new heat. But with a heat pump, you're not making new heat. You're just moving and concentrating what you already have. For every bit of power you put into the pump, you might get three or four bits of heat out the other side. This is because the computer already did the hard work of warming the water up part of the way. If you tried to pull heat out of the freezing cold air outside, the pump would've to work much harder. The data center gives the whole system a massive head start.

HostI can see how that works for the building next door, but what about the rest of the town? You can't just dig up every street to lay new pipes for one data center. The cost would be huge.

GuestYou're right, and that's why this usually happens in places that already have something called district heating. In some cities, especially in colder parts of the world, houses are already linked together by a big loop of hot water pipes under the streets. Instead of every house having its own furnace in the basement, there's one big heat source for the whole neighborhood. In a setup like that, the data center just plugs into the loop. It becomes the furnace for the town. In a city like Stockholm, they have been doing this for years. They have data centers that are large enough to heat thousands of homes. The people living there might not even know their morning shower was warmed up by someone else browsing the web or watching videos.

HostIt's a great fix for winter, but I keep thinking about July. No one wants a heated floor when it's already hot outside. Do we just go back to wasting it when the sun comes out?

GuestThat's the big puzzle engineers are still trying to solve perfectly. If no one needs the heat, the data center still has to get rid of it or the chips will fail. Some places are starting to pump that extra summer heat deep into the ground. They find giant pools of water in the rocks far below the surface and use them like a big thermos. They fill them with hot water in the summer and then suck that warmth back up when the snow starts to fall. If they don't have that, they do have to use big cooling towers to dump the heat into the sky. It's a bit of a balancing act between the needs of the computers and the needs of the neighbors.

HostIt feels like we're finally moving away from the idea that a building is just a box that sits by itself.

GuestWe're starting to see these giant warehouses of chips as a part of the city's life support, just like a water tower or a power plant.

HostThe same heat that used to be a problem for a computer is now the very thing keeping a family warm at the dinner table.