We are working on a 9-story residential project that is being certified v4.1 BD+C: New Construction. The spaces (including all dwelling units) are cooled by VRF indoor units and heated by radiant floor with hot water coming from a central boiler.
For the dwelling units, We are considering ASHRAE 62.2-2016 as indicated by LEED v.4.1. However, we have the following concerns:
1 - Section 4.1 of this standard states that "mechanical exhaust system, supply system, or combination thereof shall be installed to operate for each dwelling unit to provide continuous dwelling-unit ventilation with outdoor air at a rate not less than specified in Section 4.1.1.". We understand that ventilation can be supplied to or exhausted from one or more spaces of the dwelling unit, therefore we are considering using an exhaust system which exhausts air from bathrooms and kitchen areas, to comply with the mechanical system requirements (since air will transfer from other spaces within the dwelling unit to these exhaust points). Is this interpretation correct?
2 - Also the same section, 4.1, states that the ventilation must be continuous, however, section 4.2 states that "Local exhaust fans shall be permitted to be part of a mechanical exhaust system. Where local exhaust fans are used to provide dwelling-unit ventilation, the local exhaust airflow may be credited toward the dwelling-unit ventilation airflow requirement.". And section 5.1 says that the local exhaust can be either continuous or on-demand. If we use an on-demand exhaust system for kitchens and bathrooms, are we still complying with section 4.1?
3 - Section 6.1 states that "Supply and balanced ventilation systems shall be designed and constructed to provide ventilation air directly from the outdoors." and section 6.8.1 says that "Operable windows, skylights, through-the-wall inlets, window air inlets, or similar devices shall be readily accessible to occupants.". making it unclear to us if the make-up air, in case we use the local exhaust fans to comply with the ventilation requirements, can be drawn from the operable windows (that will be operated by the occupants) or if we need a permanently open louver to the outdoors?
Any insights or experience on this would be appreciated.
Sherman Aronson
Sr. AssociateBLT Architects
4 thumbs up
May 2, 2021 - 7:40 pm
I am not an expert in this topic, but our firm has invetigated this prerequisite for multifamily projects, too. It is out understanding that: 1) yes, exhaust fans can be part of the ventilation system, as you note; 2) the fans need to be continuous at the minimum level needed by calculation AND it can have a switch that allows a higher level of exhaust when an occupant wants more ventilation in the bathroom, for instance; 3) operable windows would need to be open ALL the time, which is not practical. Through the wall vents with louvers, or "trickle vents" in the wall or as part of the window system can comply. Otherwise, mechanical ductwork will need to bring outside air to each unit. That can be via horizontal ducts through the corridor and into the unit, or via vertical risers. I think there is some flexibility as to how the outside air from the duct enters the living space, but it should not short-circuit the exhaust fan location. Hope that helps. The added ductwork becomes a significant construction cost factor. On the other hand, the constant supply of fresh air helps address post-Covid, future pandemic issues.