Outside Weatherhoods
The weatherhoods must have
•no less than 10 ft. (3 m) apart from each other
•at least 18 in ( 46 cm) above snow line or ground level
•away from sources of contaminants, such as automobile exhaust fumes, gas meters, garbage cans, containers, etc.
•not exposed to prevailing winds, whenever reasonable possible
The outside perimeter of the weatherhood must be caulked to prevent leakage into the building.
The design and size of the weatherhoods or louvres chosen by the installer must allow for adequate free area. Water and debris penetration of the system is minimized when the airflow does not exceed 1000 FPM (5.08 m/s) free area velocity.
Ducting from the Weatherhoods
Galvanized sheet metal ducting with sufficient cross section with an integral single piece vapour barrier should be used to connect the HRV/ERV to the weatherhoods.
All ducting must meet UL Class 1 requirements.
A minimum R value of insulation should be equal to 4 (RSI 0.75)
A good bead of high quality caulking (preferably acousti- cal sealant) and taping with a high quality aluminum foil tape is recommended to seal the duct to both the HRV/ERV and the weatherhood.
Warmside Ducting - General
Ducting from the HRV/ERV to the different areas in the building should be galvanized metal whenever possible.
To minimize airflow losses in the ductwork system, all ducts should be as short as possible and with as few bends or elbows as possible. 45° elbows are preferred to 90° elbows. Use “Wye” (Y) fittings instead of “Tees”
(T) whenever possible.
All duct joints must be fastened with screws, rivets or duct sealant and wrapped with a quality duct tape to prevent leakage. We recommend aluminum foil tape.
Stale Air Return System
The stale air return system is used to draw air from the points in the building where the worst air quality problems occur. Balancing dampers and/or adjustable grilles are recommended on all return air lines which are used during installation to help balance the “draw” from different areas of the building.
Alternately, the stale air may be drawn directly from the return air duct. When this system is used, the air handler’s blower must constantly operate. The exhaust takeoff connection must be at least a 3 ft (1 m) from a directly connected HRV/ERV supply duct if both are connected to the same duct run. Static pressure of the air handlers return system should be noted and compensated for if, it is apparent that the static pressure of the return in the air handler will exceed
.1 to .15” W.C.
A damper located just prior to the HRV/ERV is required to balance the stale air exhausted with the fresh air supply entering the building.
Return air suction points should be located on the opposite side of the room from the fresh air inlet. The inlets may be located in the ceiling or high on the walls and fitted with inlet grilles.
Many commercial activities produce air contaminants in the form of dusts, fumes, mists, vapours and gases. Contaminants should be controlled at the source so that they are not dispersed through the building nor allowed to increase to toxic concentration levels. The ventilator allows for economical operation of the HVAC system while effectively removing contaminants from the space. In designing the exhaust portion of the system the exhaust grilles are placed so as to remove the contaminants while not allowing them to enter the breathing zone of the occupants.
For contaminants that are lighter than air, grilles should be located high on the wall. If contaminants are heavier than air, a lower placement of the grilles will be required. Information on a contaminants specific gravity and toxicity should be available from chemical data sheets.
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