Outside Weatherhoods
The weatherhoods must have built-in “bird” screen with
1/4 in (6.35 mm) minimum mesh to prevent birds and
rodents from entering into the ductwork. Do not use
smaller mesh as it will be very susceptible to plugging
up. Gravity dampers at the vents must not be used as
they will restrict air flow and often “seize up”. The pre-
ferred location of the outside weatherhoods is:
• 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 snow penetration of the system is mini-
mized 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 sec-
tion with an integral single piece vapour barrier should be
used to connect the HRV to the weatherhoods. All duct-
ing 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
and the weatherhood.
Warmside Ducting - General
Ducting from the HRV to the different areas in the build-
ing 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 pre-
vent 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 prob-
lems 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 han-
dler’s blower must constantly operate. The exhaust
takeoff connection must be at least a 3 ft (1 m) from a
directly connected HRV supply duct if both are con-
nected to the same duct run. Static pressure of the air
handlers return system should be noted and compen-
sated 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 is required to
balance the stale air exhausted with the fresh air sup-
ply 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 contami-
nants 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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