This BOD section should be referenced and applied in all new construction projects as well as any projects involving work on ventilation components or systems in POAH developments. This section should also be referenced during planning activities to guide the scope of pending renovation to existing buildings.
Ventilation has significant impact on resident health, resident satisfaction with the living environment and on building energy use. Historical building ventilation approaches are unlikely to provide appropriate ventilation in modern buildings or for modern expectations. It should not be assumed that new systems designed to meet current code standards will deliver effective and efficient ventilation in multifamily buildings.
The purpose of ventilation is threefold:
Removing airborne contaminants is the work of source control ventilation (ie range hood and bath exhaust fan). Diluting distributed airborne contaminants and providing fresh air is the work of general background ventilation.
Historically, buildings relied upon leaks in the building enclosure and open windows to provide ventilation. Source control ventilation is often ineffective in this approach. General background ventilation rates are neither controlled nor reliable. The random leaks of this approach bring severe detriment to comfort, energy costs and pest control.
More recently, the need for mechanical ventilation was recognized and exhaust fans were used to move air in and out of buildings. While providing more reliable source control ventilation and some control of general background ventilation rates, these systems still relied on a leaky building enclosure. The air exhausted from the building was replaced by air "leaking" back into the building. The "exhaust-only" approach affords no control of where the make-up air comes from. Instead of being fresh air, the make-up air for apartment exhaust may be drawn through building cavities and from neighboring apartments.
Today, our goal is to make our building enclosures air-tight and avoid reliance on random leaks. Therefore, ventilation systems need to include supply air. Balancing supply and exhaust air in a building supports good indoor air quality (IAQ) which is key to providing healthy homes. By removing carbon dioxide, contaminants produced in cooking activites, VOCs and excess moisture/humidity, the ventilation system improves indoor air quality and increases the long-term durability of the building by limiting the opportunity for mold/mildew growth.
In substantial rehab or new construction, building codes will dictate the amount of fresh air to be supplied to buildings and units (general background ventilation). They also establish the amount of air that needs to be exhausted (source control ventilation) from building spaces where airborne contaminants are often generated such as laundry and trash room, as well as kitchens and bathrooms within apartments. While codes dictate the volume rate of ventilation, the codes do not provide for ventilation effectiveness. For example, the code provisions do not ensure that intended fresh air actually reaches apartments nor that source control ventilation actually captures or contains airborne contaminants. The codes also do not require ventilation systems to be optimized for operation expense and energy use.
Because of this, POAH needs engineers for substantial rehab or new construction projects to design a ventilation system that is not only code compliant but also effective and energy efficient. The ventilation design will be reviewed by Design & Building Performance and the energy consultant (if applicable). The engineer will also be asked to provide data on ventilation system energy use, flow rates and other system parameters as means to demonstrate the energy efficiency and effectiveness of the design.
For property managers and maintenance staff replacing fans or roof top units, please use the preferred products highlighted below. If new equipment is being installed contact POAH for guidance.
The sections below outline preferred and acceptable ventilation strategies. The strategies are arranged as follows:
This approach generally employs continuous exhaust flow to achieve source control of excess humidity and odors. Where a shared exhaust riser and roof-top fan are used to provide continuous exhaust from apartment bathrooms, POAH prefers the following measures:
CFM: 30 - 110
one: 0.3 - 0.8
CFM/Watt: 11.5 - 15.1
Building codes allow for kitchen exhaust ventilation to be either 1) intermittent or 2) continuous. Intermittent kitchen exhaust is preferred as it 1) provides for more effective source control (capture efficacy) and 2) results in less aggregate ventilation load.
Codes also allow for kitchen exhaust through either a capture hood over the cooking appliance or through a general area exhaust grille located in the cooking area. The capture hood is preferred as this approach has the potential for reasonably effective capture efficacy of cooking effluent. The general area exhaust is not effective.
Sample products are located in the RANGEHOOD page of the APPLIANCES section:
Balanced energy recovery ventilation (ERV) or heat recovery ventilation (HRV) is preferred in all climates excepting Climate Zone 2a. There are three different general approaches to providing this kind of background ventilation to apartments:
Individual apartment ERV/HRV offers the advantage of apartment-level control, off-the-shelf products and minimized risk of cross-contamination between apartments. It brings the challenges of distributed in-unit equipment that requires periodic maintenance. Ventilation using a separate ERV/HRV for each apartment will require at least one through-wall penetration per apartment for the fresh air intake and stale air vent. However, this approach supports compartmentalization as vertical shafts between floors and penetrations through interior separations are not needed for general apartment ventilation.
DUCTED ERV/HRV WITH CROSS-FLOW OR COUNTER-FLOW ENTHALPY/HEAT EXCHANGE CORE:
These systems will require one or more exterior wall penetrations per apartment. The ducting allows for distribution of ventilation air and can provide a degree of air mixing (to prevent stagnation) within the apartment. (The ventilation may also be integrated with heating and cooling ductwork, provided 1) proper design and controls are implemented to minimize air handler fan energy 2) allow ventilation distribution and 3) prevent short-circuiting of the ventilation supply to the stale air exhaust) If sized properly, these systems can provide bathroom source control ventilation. Typically installation of these systems will occur in soffits or a ceiling plenum in which to run ductwork as well as an area (e.g. upper part of closet) where the equipment could be located. The product shown is RenewAire.
ON THE HORIZON:
As of Spring 2017, two manufacturers are beginning to offer heat pump heat recovery units to the US market. These units offer ventilation and dehumidification with the ability to provide a modest amount of heating and cooling. Once these products achieve a successful track record, they will offer an interesting solution for complete apartment-side conditioning and ventilation for low load buildings.
This approach can reduce or eliminate the need for vertical ventilation ducts in a building. Economies of scale can be achieved by sharing ventilation equipment among several apartments. These economies may afford the installation of high quality and highly efficient equipment. Some ventilation equipment may offer economizer capabilities to provide free cooling. This approach may present challenges in balancing the ventilation airflows to each apartment. If sized properly, these systems can provide bathroom source control ventilation. Maintenance requirements of the ventilation system are met without the need for access to apartments. This approach entails a challenge of routing ductwork horizontally through corridors (above the ceiling) and of crossing fire separation assemblies with ductwork. In existing buildings, the deck-to-deck height may not be able to accommodate horizontal ductwork along corridors.
This approach may be most suitable for existing buildings with existing exhaust and ventilation supply risers through the building. This approach allows for minimizing the number of penetrations through the exterior enclosure but will require many penetrations through assemblies within the enclosure. Economies of scale can be achieved by sharing ventilation equipment among several apartments. Larger and more sophisticated equipment may offer useful functionality such as enthalpy economizer functionality, variable speed demand control, etc. Typically, commercial-sized ERV/HRV equipment offers only modest recovery efficiency (note the exception of Ventacity with its exceptional performance). Maintenance and controls may require specialized skills. A central ERV/HRV will require vertical shafts through the building. This approach will present challenges in balancing the ventilation airflows to each apartment. In existing buildings, the deck-to-deck height may not be able to accommodate horizontal ductwork along corridors.
The following preferred strategies apply to trash rooms, janitor closets, elevator machine rooms and other areas outside of apartments where airborne contaminants are generated.
Preferred strategies will ventilate corridors as per the requirements of that space plus additional supply airflow commensurate with common area exhaust of spaces such as trash rooms, janitor closets, elevator machine rooms that are directly attached to the corridor. The ventilation design for new and renovation projects shall not employ the corridor as a make-up air plenum for apartment exhaust (unless the project is over 54 ft in height and is in Chicago where physics of air are different – hence “Windy City”).
Providing hallway ventilation by ERV or HRV will significantly reduce the thermal load of the hallway ventilation air. It will bring a slight increase in fan energy however this may be mitigated by high efficiency equipment.
Independent of which common are ventilation strategy is used, all unit entrance doors need to be weatherstripped to maintain unit compartmentalization.
Door Weatherstripping at Head and Jamb
Polyethylene-clad urethane foam secured to a PVC carrier.
Door Weatherstripping at Sill
36" Fire-Rated Door Sweep Aluminum
If there is no feasible way to vent directly into units (ie because hallway ceiling height is too low), the following configuration may be allowed. If air is supplied to the corridor in equal (or more) volume to the volume of air exhausted from the apartment units, this is NOT a balanced system. Instead, it creates an unbalanced supply ventilation system for the corridors and an unbalanced exhaust ventilation system for the apartments. Supplying pre-conditioned, filtered outdoor air to the corridors only marginally improves the situation for the adjacent apartments with the unbalanced exhaust ventilation systems. In very few locations it is permissible to assume air supplied to corridors will enter units though an undercut door. Most fire codes don't allow this. This also eliminates any compartmentalization from unit to hallway.
The steps below are suggested for situations where direct ducted supply air to units or individual/HRV/ERV are not possible.
With all of these improvements, there is now much less air being sucked out of the building. There would be less fan energy, better contaminant control, less thermal energy to heat the air drawn in by the exhaust, and smaller equipment on the roof.
Supply fresh air to the corridors based on square feet and CFM exhausted from corridor ventilation (something like 6 cfm per 100 sf), trash rooms, janitor closets and elevator machine rooms (if the ventilation supply rate to the corridor is more than the exhaust from connected trash rooms and such, then you shouldn’t need to bump up the supply). The design supply ventilation rate drops to about 1/5 or less of what it previously was.
More likely, you’re to have a situation (especially in Chicago if the building is over 53ft high) where engineers insist on supplying to the corridors an equal volume to the exhaust from the apartments. This is far from optimal and in no way represents a balanced system.
Again, the unit entry doors should be gasketed and weather stripped. And so should doors to stairs, doors to trash rooms, doors to elevator lobbies…