I searched the threads and only found this old one talking about CO2-based On-Demand Ventilation: http://hvac-talk.com/vbb/showthread.php?t=169032
My thought is - is there any manufacturer who sells a thermostat that can adjust the ventilation rate based on combined logic using CO2 and humidity? That is - to only run when there is a demand for CO2 or humidity adjustments?
I read an excellent article investigating the idea at
The guy is an electrical engineer. His article states that, based on demand, he found that his on-demand HRV would run, reactively,:When I wrote him he said this:9% of the time just sampling
25% of the time purging CO2/humidity
The remaining 66% of the time it is off because it isn't needed.
Obviously if you used a timer to turn it on 25% of the time you would exhaust the right quantity of air, but there is no way it would be timed right. Furthermore, without the controller, I would never have known that 25% was ...average... This of course is the whole problem with rules-of-thumb and sizing units based on the suggested number of air exchanges per hour. There are too many variables, so unless you have some way of measuring the pollutants in the air, you are just taking a wild guess.
If I can have my HVAC contractor do something off the shelf, even better."Other than the one I made for myself, I am not sure they exist anywhere for sale. I will make a printed circuit board for it later this year (the current one I have is hand soldered together using perf-board and the display is inserted into a box carved out of a piece of leftover 2x4
spruce). When that happens, I can manufacture a bunch of them easily for anyone that wants one. I am currently gathering data and will probably use
it as an Engineering Masters degree project and work out the math for the optimal control algorithm."
Thanks for your thoughts,