Warmup/Cooldown; Damper Control; Make Up Air; Damper End Switch - EngA ENGINEERED AIR base Technical Manual

base
the air switch close (prove) within 30 seconds. If the switch does not close, the low air flow alarm is triggered.
If during normal operation, the flow proving opens, a 15 second low air flow lock out timer is started. During
this time, compressors and heat exchanger style burners are allowed to stay running. Once the 15 second timer
has elapsed, the equipment will shut down on low air flow alarm.

WARMUP/COOLDOWN

A blower warmup/cooldown delay may be required to preheat or cool down the heat exchanger. For DG and DJ
style heat exchangers a full heat exchanger warm up delay is required when the ambient temperature is below
the low limit set point or when the ambient temperature is 8°F (-13°C) or colder than the discharge set point
but above the full warmup required ambient.
The base blower delay off time is automatically set according to the application and type of heating device,
according to the table below.
Application
MUA
Mixbox
*The damper off delay starts when the blower is shut off

DAMPER CONTROL

MAKE UP AIR

Make up air equipment will normally use a 2 position actuator to open or close the inlet dampers.

DAMPER END SWITCH

Used with a 2 position damper actuator, the damper end switch input is for a mechanical device used to prove
the dampers have opened. The switch may be independent, or an auxiliary contact from the damper actuator.
If used, after DM is enabled, when the damper end switch 'makes' and inputs 24Vac to terminal DES, the fan
delay timer is set to zero, and the fan will start.

AMBIENT COMPENSATION

On blow through heat exchangers, the blower sees greatly varying inlet temperatures. As the air temperature
changes, so does the air density and volume. The blower delivers a constant volume of 'cold' air. As this air is
warmed by the heat exchanger, it expands causing the outlet air volume to increase. With the extra air
volume, the temperature rise is reduced and there may not be enough heat on a design day.
The ambient compensation attempts to correct this by partially closing the inlet damper enough to add enough
system static to compensate for the expansion effect. The compensation starts to reduce the damper opening
at 30°F (-1°C) and reaches maximum effect at -40°F (4°C) . The low limit operation has no effect on the
IOM74
* Damper delay Exchanger Warm
up delay
DJ: 75 sec
On 90 sec
DG/DJX: 75 sec
Off 20 sec
Other: 0 sec
DJ: 75 sec
On 10 sec
DG: 75 sec
Off 10 sec
Other: 0 sec
14
A
Cool down delay
DJ: 90 sec
DG: 90 sec
DJX : 90 sec
HE: 8 sec
Other: 30 sec
November 2020 R105