DIY ventilation heat exchanger

[AC_Hacker]

I have been looking into ways that the air-exchange rate of an HRV/ERV can be controlled.

Conversations with local Green and Passive House contractors have confirmed that HRVs/ERVs with CO2 sensor controllers are being used now. But they look frightfully expensive.

So, a CO2 sensor can be used to control the speed of an HRV/ERV by varying the duty cycle of a pulsed DC wave form driving a fan.

CO2 sensors are available in various configurations on ebay.

I am investigating the possibility of using variable-speed computer fans, since they are highly evolved and are cheap. A potential problem I have recognized is that there may be a problem with using computer fans in an environment that is operating close to the dew point.

Seems that moisture can drastically shorten the bearing life of the computer fan. I have also seen ECM fans that move the motor and it's bearings out of the air flow, so bearing life wouldn't be so affected by moisture. Fans of this configuration are also called Tangential Blowers. Trick is to find one with an ECM motor.

I have also found out that speed-control chips are made for these fans, and the chips are in high-volume production and are also cheap.

So far, the control chips have various steps to control the fans, some chips have 4 steps, others have more. I have also seen Arduino projects where an Arduino board out-puts varying PCM pulses based on an input signal...

...and some CO2 sensors intended for Arduino integration.

-AC_Hacker