ERV, Whole house dehumidifier & proper ducting.
Questions on ERV & whole house dehumidifier – ducting.
Background: San Antonio TX (2B), new residential construction completed June 2021. Single story, slab on grade, 3Br 3Ba, about 3700 sq ft. 10’/12’ ceilings. Zip R3 sheathing over conventional 2×4 stud walls, open cell spray foam, walls/ attic roof. 4ton Carrier Infinity series heat pump feeds great room, kitchen, office, laundry. 2 ton infinity series heat pump feeds all 3 bedrooms and guest & master baths. Air handlers & insulated ducting located in the sealed non vented attic. On original install. our HVAC contractor installed 2 carrier 198 cfm variable speed ERV’s one to each air handler using “simplified system” (indoor exhaust air & fresh air intake each tied to return air duct plenum upstream of air handler for each ERV). The tie ins for each of the ERV ducts into return plenum are approximately 40”-46” apart ctr-ctr. However, the exhaust air duct tie in is only 50” in each case in front of the air handler filter. The Carrier thermostat set up appears to allow for an ERV “auto setting” whereas air handler fan kicks on when the ERV auto mode is set to cycle on (ERV on auto operate at minimum speed for 20 min each hour). The internal residence temp is set to 75F and a target 50% humidity setting (I was advised by my HVAC installer not to set below 50%) and to me the rooms feels muggy and at times stale, indoor humidity levels range from 57% – 47% and seem to vary throughout the summer days. The only time we are dehumidifying is when condensers are running. We have outdoor terminated exhaust fans in each of the 3 baths & laundry and use them regularly for when rooms are occupied & then some.
I have some concerns about the effective performance of the ERVs adding proper ventilation as currently ducted. 1) Would I benefit by modifying to a Hybrid ducting of the ERVs (modify with dedicated ductwork to pull stale air back to ERV) and 2) adding a whole house dehumidifier to the 4 ton unit with separate ducted intake and output to supply plenum? And… would there be any benefit to replacing one of the ERVs (currently tied to the 4 ton) with a ducted ventilating dehumidifier like Ultra-Aire 98H?- As I understand, this would bring in fresh air much like the existing ERV? I am getting a bit overwhelmed on how best to rectify my indoor air quality Many Thanks for your consideration.
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