Direct Gas Make-Up Air
41
OPTIONAL COOLING
Optional Cooling Contact (S4) Closed
• Power passes to normally open fan relay (RF or
ST1) which is energized and closed.
• Power passes to optional inlet air sensor contact
(TS5) which is closed if the inlet air temperature is
below the set point.
• Power passes to and energizes cooling relay (RC).
• Cooling sequence begins.
Cooling Sequence - Recirculating Pump
Evaporative Cooling
• Whenever the cooling relay (RC) is energized,
power passes through the normally open cooling
relay to the evaporative cooling pump (P1).
• The evaporative cooling pump(s) are energized and
cooling begins.
Cooling Sequence - Auto Drain and Fill Evaporative
Cooling
• Power passes to the evaporative cooling module
freeze sensor (FRZ) which is closed if the incoming
air temperature is above the set point.
• Power passes to the auto drain and fill timer (TC)
and the supply drain valve (VSD).
• The supply drain valve is energized and closed.
Run Time Period
• During the run time period, the auto drain and fill
timer (TC) passes power to the auto drain relay
(RA) and to the auto drain valves (VS, VD).
• The normally closed supply valve (VS) is energized
and opens. The normally open drain valve (VD) is
energized and closes. The normally open supply
drain valve (VSD) is energized and closes. This
allows water to fill the evaporative cooling sump.
• When the cooling relay (RC) and the auto drain
relay (RA) are energized, power passes through the
normally open cooling relay (RC) contacts and the
normally open auto drain relay (RA) contacts to the
evaporative cooling pump(s) (P1).
• The evaporative cooling pump(s) are energized and
cooling begins.
Drain Time Period
• When the run time period expires, the auto drain
relay (RA) and the auto drain valves (VS, VD) are
de-energized. The drain time period begins.
• When the auto drain relay (RA) is de-energized,
the normally open auto drain relay (RA) contacts
open and the evaporative cooling pump(s) are de-
energized.
• When the normally closed supply valve (VS) is
de-energized, the water supply to the evaporative
cooling module sump is stopped.
• When the normally open drain valve (VD) is
de-energized, the evaporative cooling sump is
drained.
Freeze Condition
• If the incoming air temperature is below the
evaporative cooling module freeze sensor (FRZ) set
point, the freeze sensor (FRZ) contacts will open,
de-energizing the auto drain and fill timer (TC) and
the supply drain valve (VSD).
• When the normally closed supply valve (VS) and
the normally open supply drain valve (VSD) are de-
energized, the supply line is drained.
• When the normally open drain valve (VD) is de-
energized, the evaporative cooling module sump is
drained.
Cooling Sequence - Chilled Water or Split System
DX Cooling
• Modulating or staged controls for chilled water and
split system DX coils are supplied by others. The
sequence of operation will depend on the controls
provided.
• The cooling relay (RC) normally open contacts may
be used to initiate the cooling sequence for the
controls supplied by others.
Sequence of Operation