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Comment by pfdietz | Hacker News Reader

I wonder if air-to-air heat exchangers could address that cost issue.

Energy Recovery Ventilation (ERV)

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

Yes. I was wondering if the wheel-based ones had some means of killing pathogens on the wheel, rather than transfering them back to the incoming air stream.

I've been thinking about getting two CPU cooling fans that have the heat sink at a distance from the fan and use a heat pipe to move the heat over to the fan and connecting them back-to-back so one fan blows outward and one blows inward. Something like two of these:

http://i.ebayimg.com/images/i/151452729196-0-1/s-l1000.jpg https://prod.scorptec.com.au/10/299/65429/121859_large.jpg https://brain-images-ssl.cdn.dixons.com/7/2/10178327/l_10178...

That way outgoing air would warm (or cool) the incoming air. If a Hepa filter could be added to the incoming air fan it would make an ideal unit to put in the window at fairly low cost. Since they are CPU coolers they could probably be made speed adjustable also.

That would transfer sensible heat, but not latent heat.

Countercurrent exchange is the way to go with a scheme like this, so you'd want a series of pipes at varying temperature.

Surely all industrial / professional HVAC get installed with HRV and the loss here is going from the "100% efficient" recirc to HRV, no?

Not all if it isn't designed that way (ours isn't because we never plan to not use recirc). The loss isn't actually that much and since we are using low temp cooling water to cool the air and we have a significant amount of that on site already we barely notice (still a cost though).

How old is your building? New construction is so weather sealed and lacks fresh air leaks to meet air quality standards. Pretty sure whatever standard to get a green rating on a building requires outside air to be mixed in and due to efficiency requirements there has to be heat exchanger.

25 years...but we also have the ability to open outside dampers on our return air chases to output all air if needed.

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