21
ECONOMIZER
HRV/ERV FRESH
AIR SUPPLY
HRV/ERV UNIT
STALE AIR
EXHAUST TO HRV/
ERV
SUPPLY DUCT
RETURN AIR DUCT
or BREATHER T
ROOFTOP
UNIT
B.D.
B.D.
FRESH AIR
SUPPLY
STALE AIR
EXHAUST
FRESH AIR
SUPPLY
STALE AIR
EXHAUST
HRV/ERV FRESH
AIR SUPPLY
HRV/ERV
UNIT
B.D.
B.D.
STALE AIR EXHAUST
ROOFTOP
UNIT
12” BREATHER
SPACE
ROOF DECK
CEILING RETURN AIR PLENUM
SUPPLY DUCTWORK
Figure
A
Figure
B
The HRV/ERV has become an integral component of the
HVAC system. Figure A shows an HRV/ERV unit
providing fresh air directly to the return air plenum of
a rooftop heat/cool unit.
In the balanced airflow system, the HRV/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 obsolete in conjunction with an HRV/ERV.
Many buildings have ceiling return air plenum as in
Figure B. Fresh air from the HRV/ERV can be introduced
directly into the ceiling space but this should occur
near the air handler’s intake.
By operating the HRV/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
general exhaust from the space, the air to be
exhausted may be taken directly from the return air
plenum to the HRV/ERV as it is drawn back to the air
handler. Fresh air supplied by the HRV/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 HRV/ERV
supply and exhaust ducts between the return air
plenum and the HRV/ERV.
NOTE:
At
no
time
should
the
air
handler
T.E.S.P.
on
the
return
duct
exceed
that
of
the
HRV/ERV
.
The
Integrated
HVAC
System
When
interlocking
a
rooftop
unit
with
an
HRV/ERV,
care
must
be
taken
to
ensure
the
fans
of
both
units
operate
in
the correct
rotation.
CAUTION
ECONOMIZER