While we do not make HRVs, there is certainly some history behind them. It dates back at least to the 1970’s when sealed, energy efficient houses began popping up and the issue of indoor air quality arose. There was also an energy crisis during that time, very similar to what we are experiencing right now. HRVs are just one solution to both energy inefficiencies and air quality. Here are some more links that I hope will help with your assignment:

http://www.fantech.net/hrv_erv.htm

http://en.wikipedia.org/wiki/Heat_recovery_ventilation

http://apps1.eere.energy.gov/consumer/your_home/insulation_airsealing/index.cfm/mytopic=11900