That's what I was thinking. With an HRV/ERV you could use the CO2 sensor relay to cycle the unit. Since you are recovering most of the heat, the ventilation temperature limits wouldn't really be needed. You still might want to use the ventilation dew point limit though, depending on the local climate. I can see why most people wouldn't bother with the extra cost of a CO2 sensor. If you are getting 70-80% energy recovery, it doesn't matter as much if you are over-ventilating, and the ROI on the CO2 sensor is long.
Originally Posted by chuckcrj
With a simple supply-side fresh air intake, you could use the CO2 sensor's proportional 10V voltage output to control an actuator on a damper to let in just the right amount of air. Since there is no heat recovery, you would also probably want to use both the ventilation temperature limits and the dew point limit.
I like the CO2 control to activate fresh air ventilation when the home is occupied and the natural infiltration rate is low. I do not like the idea of not providing a small amount of fresh air ventilation when it needed. 70-80 cfm of fresh air during cold or damp weather and the home is occupied is very small energy cost. My experience is that during cold windy weather and home occupancy, little or no fresh air is needed. So small energy cost. During damp, calm weather, the full 80 cfm will be required. The cost of dehumidification is minor. Indoor air quality is more important than saving a couple bucks. Get a good ventilating dehumidifier connect to a CO2 controller set low enough to activate the ventilating when the space is occupied by one. This typically +650 PPM CO2. My experience is very little running during winter occupancy and ventilation required during calm weather whenever occupied. Lets keep this going!
Originally Posted by garya505
I think what you are saying is that you don't like the idea of the temperature or dew point limits? The temperature limits can be adjusted (and may not matter due to infiltration at the high and low end). Its normally very dry here, so the only time we would ever see a high dew point here would be on a hot summer day during a heavy rainfall, and that might only happen a couple of times a year at most. Dehumidifiers are never used here, unless maybe you have a damp basement.
Originally Posted by teddy bear
Looking at the sensors, the Honeywell kind of suck for adjustment of relay setpoint and range, and don't have an adjustment for altitude. The lowest setpoint on the C7232 is 800, and a CO2 sensor will read about 17% low here at 5000ft, so a setpoint of 800 is really about 960. So, it would work, but not for 650 PPM. The Telaire 8002 sensors are much better in that regard, with the setpoint adjustable over the full range, and an altitude adjustment as well. I think you could set it for an altitude-adjusted setpoint of 650 PPM. The Telaire would also work better if using the proportional 10V output and a proportional damper actuator, because both the low and high ends of the analog output signal range can be set. So, you could set it to start opening at 650 PPM and be fully open at whatever level you want.