©2015 Green Building Advisor. From The Taunton Press, Inc., publisher of Fine Homebuilding Magazine.
I am working on sizing an HRV for my son's house. Using ASRAE 62.2 I get 77cfm. Using ACHnatural of .35/hour I get 144 cfm. Using Venmar's tables I get 160/80 cfm for the high/ low. Using 10 cfm/room and 20cfm for master bedroom and basement I get 180 cfm. I wonder if some of the higher numbers from the manufacturers are trying to account for high speed venting of bathrooms. However I wonder even at 180 cfm with ten supply and return grilles if he HRV can pull enough air out of one bathroom to stay ahead of a long hot shower on a cold winter's night. So am thinking that I should focus on the range of 77 to 144 cfm and install bathroom (and range hood of course) exhaust fans to cover the short term heavy ventilation demands. I am using a friction loss worksheet developed by Carrier that I found on line for trying to get an idea of the static pressure the fans will be operating against in order to size the unit. So I am looking for help on criteria for determining the cfm operating range of the HRV, and a good procedure for predicting the system static pressure. Any thoughts. steve02