Even a foam house has many imperfections that allow air to leak in or out. Most will leak .1-.2 of an air change per hour in a 7 mph wind (considered an average winter wind) and stack effect. This is what keeps occupants of naturally ventilated home barely alive. In calm winds and no stack effect, natural infiltration declines to near zero and are not healthy spaces with accumulated pollutants and low oxygen.
A 2,000 sq.ft. home with 9' ceilings is 18,000 ft^3 of air volume. On a average winter day, these homes will leak 30-60 cfm of fresh air into and out of the inside space. During mild seasons with calm winds, fresh air change declines in response to the natural pressures.
Adding an ERV to these homes increases the air change rate of the home to the natural infiltration rate plus the mechanical balance air flow in/out of the ERV.
Adding a ventilating dehumidifier with make-up air effects in the air change rate of the same house by a lesser amount because the stale air must exfiltrate the home via the natural air leaks in home. The exfiltrating stale air slows or stops infiltration of fresh air depending on the size of the air leaks.
ASHRAE and AM. Medical Assn. suggest a fresh air change in 3-5 hours. An 2,000 sq.ft. home with a fresh change in 4 hours would be 75 cfm of fresh when occupied. Using 75 cfm of make-up Merv 13 filtered fresh air stop all of the unfiltered infiltrating fresh except when indoor exhaust devices (kitchen hood and clothes operated.
During colder winter conditions many home get enough infiltrating fresh air to not require mechanical fresh air. Monitoring the CO2 levels in the home will determine when the home is occupied and infiltrating fresh air is inadequate to purge indoor pollutants and need to renew oxygen.
For most homes, filtered make-up air is the most practical via a ventilating whole house dehumidifier like the Santa Fe Ultra, Broan, Trane, etc..
In defense of the ERV, it is certainly better than no mechanical fresh air ventilation. You will certianly need a whole house to maintain 50%RH during evenings and rainy days to remove the moisture that passes through the unit and moisture from the occupants. We test market a combo ERV and dehumidifier unit for the residential market. There was not enough payback to justify the investment.
Keep us posted.
Regards Teddy Bear
Even a foam house has many imperfections that allow air to leak in or out. Most will leak .1-.2 of an air change per hour in a 7 mph wind (considered an average winter wind) and stack effect. This is what keeps occupants of naturally ventilated home barely alive. In calm winds and no stack effect, natural infiltration declines to near zero and are not healthy spaces with accumulated pollutants and low oxygen.
A 2,000 sq.ft. home with 9' ceilings is 18,000 ft^3 of air volume. On a average winter day, these homes will leak 30-60 cfm of fresh air into and out of the inside space. During mild seasons with calm winds, fresh air change declines in response to the natural pressures.
Adding an ERV to these homes increases the air change rate of the home to the natural infiltration rate plus the mechanical balance air flow in/out of the ERV.
Adding a ventilating dehumidifier with make-up air effects in the air change rate of the same house by a lesser amount because the stale air must exfiltrate the home via the natural air leaks in home. The exfiltrating stale air slows or stops infiltration of fresh air depending on the size of the air leaks.
ASHRAE and AM. Medical Assn. suggest a fresh air change in 3-5 hours. An 2,000 sq.ft. home with a fresh change in 4 hours would be 75 cfm of fresh when occupied. Using 75 cfm of make-up Merv 13 filtered fresh air stop all of the unfiltered infiltrating fresh except when indoor exhaust devices (kitchen hood and clothes operated.
During colder winter conditions many home get enough infiltrating fresh air to not require mechanical fresh air. Monitoring the CO2 levels in the home will determine when the home is occupied and infiltrating fresh air is inadequate to purge indoor pollutants and need to renew oxygen.
For most homes, filtered make-up air is the most practical via a ventilating whole house dehumidifier like the Santa Fe Ultra, Broan, Trane, etc..
In defense of the ERV, it is certainly better than no mechanical fresh air ventilation. You will certianly need a whole house to maintain 50%RH during evenings and rainy days to remove the moisture that passes through the unit and moisture from the occupants. We test market a combo ERV and dehumidifier unit for the residential market. There was not enough payback to justify the investment.
Keep us posted.
Regards Teddy Bear
Thank you for the detailed explanation.
My situation might be a little different, my 2nd and 1st floor humidity level is always around 50%. It is my basement that is 55-65%. It is always more humid in the basement than outside (except when it's raining) !!!
I'm worried if I install a whole home dehumidifier rule my 2nd and 1st floor will have humidity levels drop below 50%.
Also the ducting for each floor is completely separate and there is no way to link them up. I can potentially link up 1st and 2nd floor as both units are in the attic but the basement is in the mechanical room and there is no open chase. I know because I was trying to run another dedicated outlet last year.
So, back to your recommendation.
I have two "easy" options.
1) ERV for basement
2) Dehumidifier with fresh air inlet.
Note: The basement is enclosed by concrete and only 1 side has windows. So the natural infiltration is significantly reduced compared to 1st and 2nd floor.
1) ERV
Cons and Pros.
Pros = I can take air out of the mechanical room (unconditioned) and basement (conditioned) and add fresh air.
Pro 2 = It might increase the temperature of the basement in summer which will allow the Air Condition to run longer and dehumidify.
Con1 = Potentially I can increase the humidity in summer months but most ERVs have a humidity sensor that turns the ERV off if outdoor humidity is higher than a certain limit.
Con2 = More duct work needed
2) Dehumidifier with fresh air.
Pro = Much more efficient at Reduce humidity
Pro 2 = Will bring in fresh air
Cons = Any positive pressure in basement will have a hard time to escape and might choke the system as it won't be able to pull as much fresh air because of the higher pressure difference
Con2 = Won't exhaust that much stale are and might open windows (back to square 1)
