Hacker News Reader

Comment by Retric | Hacker News Reader

Having a heat exchanger let’s you exchange large quantities of outside air with indoor air at minimal costs. Trading 70f indoor air with -30f outside air is bad, moving heat between them means could be venting air closer to -10f and only need to heat the new air from 50f to 70f

You still want a quality filter and humidity is an issue in some areas, but overall they can make a huge difference.

View on HN

Wouldn't a heat exchanger top out at equalizing the inward and outward bound air at 20F in this case?

No. Imagine that your heat exchanger is simply two touching pipes running parallel to each other, with flows in opposite directions. Incoming air will gradually warm up as it comes inwards, eventually being warmed by the air which has just left the room. You can get a much better result than just averaging the temperatures.

The idea is "countercurrent exchange": the incoming air and outgoing air travel in opposite directions through the heat exchanger. The result is that most of the heat gets transferred.

At the end of the exchanger, the warmed incoming air is in contact with 70° outgoing air, so it will be at almost 70°. Similarly, the outgoing air will be at almost -10° as it exits.

It will probably make more sense if you look at the diagram: https://en.wikipedia.org/wiki/Countercurrent_exchange

Fun fact: "An example of countercurrent heat exchange occurs in the feet of penguins, in which heat from blood in the arteries supplying the feet is transferred to blood returning to the body's core in veins that lie close to these arteries."

Reply on news.ycombinator.com