Mammoth 800 to 5500 CFM: Dedicated Outdoor Air System with Enthalpy Wheels (VHC) - Manual (Page 28)

MAMM-VHC-IOM-1A (JANUARY 2013) 28
VFD High Speed Control
High speed fan control can be achieved by connecting dry
contact controls to the field wired (FW) terminals 374 and
375 for the supply fan and 376 and 377 for the exhaust fan.
Only VFD units have the high speed option. These controls
could also be the following: DPST switch, dehumidistat,
CO
2
sensor, light sensor, heat sensor, timer, Building Man-
agement System, etc.
CO
2
Ventilation Control
VHCs can be directly controlled by a CO
2
controller (acces-
sory or field supplied) that can be connected to the supply
and exhaust high speed contact terminals (VFD units only).
As the CO
2
levels exceed acceptable limits, dry contacts
close raising high speed fan ventilation. See Figure F5.
Alternatively a field supplied CO
2
controller output can be
connected to the BMS which can then be connected to the
supply and exhaust fan modulating signal input terminals
(VFD units only). As the CO
2
levels rise and fall the BMS
must modulate the signal to the supply and exhaust fans to
change the ventilation rate proportionally. See Appendix G .
The minimum VFD speed is factory default set to 40 Hertz.
301
302
304
305
305
306
307
308
320
321
322
323
324
325
326
327
328
329
UNOCCUPIED
RECIRCULATION
CONTACT (OPTIONAL)
CR
Figure F3: Unoccupied recirculation for electro-mechanical
controls (EMC) units
301
302
304
305
305
306
307
308
320
321
322
323
324
325
374
375
376
377
CR
CR
CR
OCCUPANCY
CONTACT
SUPPLY BLOWER
HIGH SPEED CONTACT
EXHAUST BLOWER
HIGH SPEED CONTACT
Figure F4: VFD high speed control
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 F5: CO
2
ventilation control
IMPORTANT
Removal of dry contacts that close on high speed termi-
nals is required for VFDs to modulate.