Monitoring Requirements - Naturally Ventilated Residential Units

Mario, This is fairly new territory for all of us, so I'll share a few thoughts despite not having an answer. First, I would submit the question directly to USGBC via the LEED Coach email address and include your project number. As I read the requirements, if you are using an exhaust ventilation scheme, then you would need to monitor that CFM, not OA in the exhaust system (kitchen and bathrooms), which seems doable? Why wouldn't monitoring the exhaust system be feasible? The first and third bullet under naturally ventilated spaces on page 606 of the BD&C RG seem reasonable, but the second one does not. All of that said, I'm not finding any comparable requirements for monitoring in the Homes RG, and in my limited experience in dealing with v4 residential ventilation, USGBC has been leaning toward ASHRAE 62.2 and the Homes requirements when questions arise about how to deal with MF ventilation requirements in v4. If you are meeting ASHRAE 62.2 in the units, you should be ok, but follow-up with USGBC to confirm, and specifically call out any concerns about monitoring requirements.

Hi Mario, I recently ran across a LEED Interpretation #10461 that provides an exception to the monitoring requirement for systems that have an outdoor intake flow of 1000 CFM or less. That does not entirely answer your issue though. The new version of 62.1-2010 requires mechanical ventilation when natural ventilation is not available - so if you are not going to provide supply ventilation, then you need your bath fan to also serve as a whole house fan and provide ventilation when the windows are closed. The source of make-up air is also something to consider depending on your local code requirements. We have been using two speed fans in these situations. The fans run continuously at low volume (30-40 CFM depending on the size of the unit) for whole house ventilation and then have a built in occupancy sensor to ramp up to a higher flow rate when the bathroom is occupied.

See below info from the LEED User intro to this credit.  This is a big topic for multi-family residential that intends to use windows for code compliant ventilation.  Perhaps it is possible for oversized bath exhausts to work, but how does the outside air get into each unit?  That becomes a mechanical ventilation system?  Thanks.  The prerequisite has different compliance paths for mechanically ventilated and naturally ventilated spaces, and you may need to follow both paths for the same building on a space-by-space basis. In fact, teams should beware that ASHRAE 62.1-2010 effectively prohibits natural ventilation via operable openings as a stand-alone strategy. This is because the standard requires spaces to be mechanically ventilated whenever the operable windows are closed. Multifamily residential buildings may be most impacted by this type of scenario.  

LEED Residential – Multifamily requires ASHRAE 62.2, not 62.1 for dwelling units. For ventilation of dwelling units to meet minimum IAQ requirements under LEED Homes Multifamily Midrise (per 62.2) we've typically seen four general strategies accepted by USGBC in our region/ climate (Pacific NW, Climate zone 4C, Marine):  

1. A Packaged Terminal Heat Pump (PTHP) in a dwelling unit that provides intermittent mechanical ventilation of outside air, and passive infiltration when the bathroom fan is providing exhaust. In a one- bedroom unit there's often one PTHP in the living room and an electric resistance heater in the bedroom;
2. A passive “trickle vent” either as part of the window frames or a thru-wall passive outside air vent in each room. Window trickle vents can be blocked or closed off by the occupants, so can be more prone to “pilot error.” Both the PTHP and trickle vent options can pose thermal comfort challenges in colder climates. I’ve also heard issues with PTHPs in high-rise apartment buildings where the height increases wind & pressure differences, and thus more cold air infiltration.
3. Ducted outside air provided unit-by-unit. In some projects we’ve seen a small heat-recovery ventilator (HRV) or energy recovery ventilator (ERV such as Panasonic) serving the bathroom or living room. The incoming cold outside air is tempered by the outgoing warm exhaust.
4. Ducted outside air delivered to each dwelling unit by a central distribution system. In a building with internal corridors, there needs to be conditioned ventilation provided to the corridor, often from a vertical shaft from a roof top mechanical penthouse with air handler, heating and cooling. Small ducts can be extended off the corridor trunk to provide outside air to each dwelling unit. Since this air isn’t providing the space conditioning load, only ventilation, the volume of air is less, and duct sizes are smaller.  This system can also take advantage of heat recovery at the roof top air handler if there’s central exhaust in vertical shafts going to the roof. The more efficient the HRV, the more you can down-size the heating equipment needed to temper the outside air.

Operable windows alone may meet code for ventilation in some jurisdictions but doesn’t meet LEED Homes or NC. In all cases you’ll need to consult with a mechanical engineer to ensure the equipment or passive vents can provide sufficient air flow. Providing outside air via an under-cut entry door from a pressurized corridor hasn’t been allowed under any version - poor odor & noise control, hard to ensure adequate air flow. We’ve found LEED Homes for Midrise v3 and v4 (which in some cases have been allowed for high-rise projects) to be a better fit for multi-family residential projects than LEED BD&C NC v2, v3, v4. The new LEED Residential Multifamily rating system in 4.1 appears to be merging the Homes and NC programs, but being so new I can imagine more uncertainty about the requirements and compliance paths. For example, I’m baffled by the 4.1 requirement “Makeup air systems must have a means of closure and be automatically controlled to start and operate simultaneously with the exhaust system.” That seems to eliminate trickle vents. That might be the intent given the thermal comfort issues in colder climates, but in milder climates they might make sense.   Since 4.1 is a draft version, and they say “We appreciate any feedback on the current draft content,” here’s an opportunity for input!