Sizing and Locating ERV
I am looking at putting an Energy Recovery Ventilator into my 6000 sq. ft. home (calculated by measuring the exterior on Google Earth and doubling it for the number of floors; seems high. It’s a 4-bedroom house.).
Our house has spray foam insulation and no ventilation, so if we don’t run the bathroom fans the CO2 level sits at around 2000ppm. If we run a 110 cfm upstairs bathroom fan constantly, it drops to around 450-500ppm after about 4 hours.
The home has separate HVAC units for upstairs and downstairs. The upstairs unit is a 3.5t heat pump, the downstairs is a 2.5t heat pump. The upstairs unit runs probably 2-3x as often. The upstairs is the main living area and has windows on all sides. The downstairs level is partially underground (about 3-4′) and only has windows on one side. We live in Delaware.
I’m looking for any thoughts — we can only afford to mount one ERV unit (quoted approx. $6k cost due to difficult ventilation work to the outside). It will work through the existing return ducts. Should we mount it on the downstairs unit or the upstairs unit?
I’d rather mount it downstairs if possible, because I work all day in the same room as the upstairs system, and I don’t want to add to the noise level. But I’m not sure that it will work well enough if the downstairs system doesn’t run all that often.
Also, we were quoted 3 options for ERV units, all about the same price and all from Carrier/Bryant:
– ERVCRLHB1200: Enthalpic transfer medium; 80-198 CFM; 41-60 sensible recovery efficiency (86-72 apparent); .47-.60 LMT
– ERVCRSVB1100: Enthalpic transfer medium; 35-105 CFM; 60-67 sensible recovery efficiency (75-79 apparent); .48-.61 LMT
– ERVXXNVA1090: Enthalpy paper; 52-128 CFM (vent-mounted); 55-60 sensible recovery efficiency (69-76 apparent); .48-.56 LMT
Which one makes the most sense?
I’m asking because the company we are planning to use admits that they don’t really know what they are doing with ERV units, but that’s true of others around here too apparently. I tried calling around and other shops said that they won’t even do ERV units or just never returned my call.
Any help is greatly appreciated!!
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