ERV Design
I am working on a Habitat for Humanity passive house in climate zone 5 on the East coast. I had some questions on the design of the ERV. The house is 1400 SF with 500sf upstairs with 2 bedrooms and a full bath. The first floor has 1 bedroom and a full bath.
The Hers rater and the supplier of the ERV system have provided a design. The 130cfm ERV is to be installed in the basement with one intake in the basement and the second intake in the common space on the second floor. The system will have one discharge into the open space on the first floor.
A 200cfm range hood will direct vent to the exterior. Both bathrooms will have 50 to 80 to 100 cfm switchable fans direct vented to the exterior controlled with a humidistat. Recommendation is to set the fans to 50cfm.
This doesn’t match the typical design that I have seen on this web site. Exhaust from the bathrooms and the kitchen and supply directly to the bedrooms. Should this be a concern? Does it make sense to exhaust from the basement? The basement is considered unconditioned space.
With this design there will be 6 vents to the outside. 2 bath fans, 2 vents for the ERV, Range hood and the clothes dryer. Should we have this many vents for a Passive House construction?
Thanks for your help
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Replies
What is the climate zone? Are there no heat, supply or return ducts in the basement?
What you described is the ideal scenario, although I'd add supply to the main living area along with the bedrooms. What they described is the cheaper/easier solution.
The house is in climate zone 5. There is no heat in the basemen.t
In most cases it is cheaper to run ducts from the ERV to each bath and skip bath fans. This saves the cost of a bathroom fan and wall termination and doesn't need a lot of extra ducting.
The kitchen range hood is a must and should be vented outside. A sperate kitchen stale air pickup for the ERV is a good idea as cooking tends to be the largest source of indoor pollution in the house. This pickup should be kitty corner from the range hood at least 8' away.
The stale air pickup in the basement is a good idea. In areas with radon it can serve dual purpose to vent any radon/basement smells plus draw in conditioned air from the floor above.
I would question dumping unconditioned fresh air in a single pickup into living space in Zone 5 unless you have a high efficiency unit or there is a post heater. When it gets into those low single digit days, the fresh air supplied can be a fair bit bellow room temperature and can create local comfort issues. My recommendation would be to run the fresh air supply to the return on the HVAC and have it both condition and distribute through the house.