24
Fresh Air Supply System
The fresh air supply ductwork from the ERV may be
directly connected to the return air duct of the forced air
system. Check the air flow balance of the ERV with the
air handler blower both “ON” and “OFF” to determine that
it does not imbalance the ERV more than 10%. Also, it is
advisable to include a short length of flex duct or other
non-metallic connector in this hard ducted line in order to
keep the ERV acoustically isolated and separately
grounded (electrically) from the air handler. This will
avoid a possible shock hazard to service people if a short
to ground develops in one of the devices.
It may be necessary to install a separate fresh air supply
ductwork system if the heating is other than forced air.
When installing an ERV, the designer and installer should
be aware of local codes that may require smoke detec-
tors and/or firestats in the HVAC or ERV ductwork.
Because an ERV is designed to bring fresh air into the
building, structures may require supply voltage interrupt
when smoke or flame sensors are triggered, or when a
central fore alarm system is activated.
Supply air grilles may be ceiling or high wall mounted.
Avoid locating incoming fresh air grilles that could cause
a direct draft on the occupants.
The use of balancing dampers or adjustable grilles to bal-
ance the flow rates into various rooms is recommended.
The use of balancing dampers or adjustable grilles as
supply air diffusers and air exhaust covers are recom-
mended. TECHGRILLES™ are round, efficient, sound
absorbing devices available in 4”, 5”, 6” and 8” (100, 125,
150, and 200 mm) models.
The Integrated HVAC System
The ERV has become an integral component of the
HVAC system. Figure A shows an ERV unit providing
fresh air directly to the return air plenum of a rooftop unit.
In the balanced airflow system, the ERV exhaust
removes stale room air (eg. from lunch room, storage or
copy area) and returns to the space an equal amount of
fresh outdoor air, making the use of an economizer obso-
lete in conjunction with an ERV.
Many buildings have ceiling return air plenum as in
Figure B. Fresh air from the ERV can be introduced
directly into the ceiling space but this should occur near
the air handler’s intake.
By operating the ERV on a 24 hour/7 day battery backed
timer the unit can be set to operate only when occupancy
or indoor conditions require the air exchange.
In installations where it is satisfactory to provide gener-
al exhaust from the space, the air to be exhausted may
be taken directly from the return air plenum to the ERV
as it is drawn back to the air handler. Fresh air supplied
by the ERV is then introduced directly into the return air
plenum but at a location closer to the air handler. The
air handler would have a constant running blower to
effectively distribute the fresh air and remove the stale
air. Balancing dampers would be located in both the
ERV supply and exhaust ducts between the return air
plenum and the ERV.
NOTE: At no time should the air handler T.E.S.P. on
the return duct exceed that of the ERV. Supply Air
T.E.S.P.
AIR FLOW
SUPPLY
AIR FLOW
EXHAUST
Figure
TECHGRILLE™ (optional) schematic
