CO
2
Ventilation Control
VHC units’ air volume with the VFD motor control option
can be directly controlled by a CO
2
ventilation control (ac-
cessory or field supplied) by connecting normally open
high speed contacts to the supply and exhaust fan high
speed input terminals for two-speed (High–Low) ventila-
tion control. See Figure H6. Alternatively, connect the CO
2
ventilation control 0 to 10 VDC output signal to the supply
and exhaust fan modulating (0 to 10 VDC) input terminals
for proportional ventilation control. See
. As
the CO
2
levels exceed acceptable limits, dry contacts
close or VDC increase raising high speed fan ventilation.
VFD motor control is factory limited to a minimum motor
speed of 40 Hz or 2/3 air volume.
Smoke Detector
Locate in a normally occupied area of premises. Recom-
mended for compliance to NFPA 90A and IMC Code 606.
VHCs can be equipped with a duct mount smoke de-
tector which will monitor the air when passing through
the duct system into the VHC. When sufficient smoke is
detected, an alarm condition is activated. By connecting
the occupied timer/sensor contacts to the NC (normally
closed) alarm auxiliary contacts on the duct sensor, an
alarm condition will open the auxiliary contact and stop
operation of the VHC.
IMPORTANT
This wiring configuration cannot be used on DDC units
that are scheduled on/off through software.
IMPORTANT
Removal of dry contacts that close on high speed termi-
nals is required for VFDs to modulate.
301
302
304
305
305
306
307
308
320
321
322
323
324
325
374
375
376
377
HIGH SPEED
CONTROL (SUPPLY BLOWER)
HIGH SPEED
CONTROL
RELAY CR1
OCCUPANCY
CONTACT
CR
TB-1
TB-2
TB-1
TB-2
TB-3
TB-4
TB-5
RELAY CR1
RELAY CR1
HIGH SPEED
CONTROL (EXHAUST BLOWER)
3
5
4
6
Figure H6: CO
2
ventilation control
301
302
410
411
24V 24V NC C
1 2 15 16
Figure H7: Smoke detector
VCES-VHC-IOM-1F – VHC-36, -42 & -50
46