Cooling; Mechanical Cooling; Pressure Sensing; General Timing - EngA ENGINEERED AIR base Technical Manual

base

COOLING

The base may control simple fluid based cooling devices (chilled water or glycol) from the auxiliary cooling 0-
10Vdc output. Expansion module(s) for mechanical cooling are necessary for staged or modulating mechanical
cooling. Refer to the C-XM cooling expansion module section.
The MCW (Modulating Chilled Water) output is a 0-10Vdc signal, with 0V=no cool and 10V=max cool, typically
associated with a chilled water coil. Reversing function must be done at the actuator. A spring return
actuator would be required for applications desiring full open, full closed, or full bypass when the equipment is
off.

MECHANICAL COOLING

The base can control up to 5 stages of mechanical cooling and will sequence on and off compressor stages to
attempt to maintain the discharge temperature setpoint. As with all staged systems, expect the discharge
temperature to fluctuate from setpoint as compressors are turned on and off. Interstage and anticycle timing is
5 minutes, non-adjustable.
Mechanical cooling is disabled below the design low ambient lockout setpoint, typically set at 50°F (10°C) for
mixed air appliances, and 58°F (14°C) for makeup air appliances.

PRESSURE SENSING

The internal pressure sensor will measure the required variable flow in a direct fired heater. The sensor is
rated at 0-10mbar (0-4"wc).
CAUTION:
Do not blow onto the pressure ports. Excessive pressure will damage it. The ports are
fragile and should not be tampered with.
At power start up, the base will perform a check of the pressure sensor. Primarily for testing for kinked
tubing, if any pressure is present at the sensor the yellow light will turn on solid for 2 seconds then revert to
normal operation.
The air pressure monitoring system performs a time weighted calculation based on severity of change to
provide some protection against nuisance lock outs from various sources, such as wind gusts. Once the airflow
has stabilized, the timer is reset. For timing values refer to the HE alarm list.

GENERAL TIMING

Mode Change time
Damper delay off
Supply low airflow alarm
Shorted Damper End Switch
Supply air shorted air switch alarm
Low limit bypass (with heating)
Low Limit bypass (without heating)
IOM74
1 minute
20 seconds
30 seconds
1 second
30 seconds
4 minutes + 30 second anti-nuisance
2 minutes + 30 second anti-nuisance
16
A
November 2020 R105