Sizing an HRV unit
I am renovating my 1903 2 1/2 story colonial house in southern connecticut, zone 5a. The house is listed as 2,100 sq ft (ground floor + 2nd floor), but I am also finishing and including the attic into the building envelope, giving an additional 1,050 sq. ft. for a total of 3,150 sq. ft. of conditioned space. I will be using closed cell spray foam insulation in all walls and roof. Heating is hydro air, and cooling is central air. System is split on 2 units, one for 1st floor and one for the 2nd floor and attic.
My question is in regards to the size of the HRV units. I am going to install 2 units and connect them to the return duct of each air handler. I called tech support at Fantech, and they recommended that I use 2 SHR1505R units. These units cover up to 3,600 sq. ft.. each and deliver between 50-149 cfm. According to my ASHRAE 62.2 calc, the whole house only needs 61.5 cfm. (3,150 sq. ft./100) + ((3 bedrooms +1) * 7.5)
So it seems to me said the rep at Fantech grossly oversized the unit. Also, should each HRV provide the 61.5 cfm, or should I split it between the 2 zones of the house? In other words, 1,050 sq. ft. first floor and 0 bedrooms, so 10.5 cfm required for one unit. Unit for 2nd floor and attic would require 51 cfm (2,100 sq. ft. and 3 bedrooms).
Hope this makes sense and thank you all in advance for your help,