39
3 to 25 Ton Modulating ERV
The modulating ERV is an intelligent ERV with variable speed
fan motors. The ERV can provide a variety of volumes of out-
side air and offset it with different exhaust speeds. CO
2
sensors
can also be tied into it for demand controlled ventilation
(DCV) operation. The modulating ERV will operate based on
occupancy and the rooftop’s operating mode, the following
sections explain operation in detail. Refer to Fig. 15 for the
overview flow diagram of a modulating ERV operation.
Fig. 15 — Modulating ERV Control and Operation Flow Chart
YES
NO
YES
NO
YES
NO
Notes:
* Min CFM represents the minimum outside air CFM requirement based on CO
2
values and setpoints.
** Occupied also means being in the unoccupied period but configured to run.
NO
YES
Is there
frost on the
wheel?
YES
NO
Is unit
occupied**
and IDF on?
NO
YES
ERV Mode = OFF
Wheel = off
ERV 2POS Damper = Closed
OA CFM = 0
Ex CFM = 0
ERV Mode = Test
User sets ERV to desired values for
testing purposes
OAU OA Fan Speed Test→OA.OF
OAU PE Fan Speed Test→OA.XF
OAU 2-position Damper Test→OA.DM
OAU Wheel Test→WHL
ERV Mode = Free Cooling
Wheel = stop-jog
ERV 2POS Damper = Open
OA CFM = Between Min CFM*
and 100 dependent on Econ Pos
Ex CFM = OA CFM - Ex CFM offset
ERV Mode = Defrost
Wheel = On
ERV 2POS Damper = Open
OA CFM = 0
Ex CFM = Min CFM* in effect
- Ex CFM offset
ERV Mode = ERV or DCV Mode
Wheel = On
ERV 2POS Damper = Open
OA CFM = Min CFM*
Ex CFM = OA CFM - Ex CFM offset
START
TEST
(RTU in test
mode)
COOL
(RTU in
Cool)
VENT
(RTU in Heat,
or Vent)
Is
economizer
open>than
5%?
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