Heating Operation; Humidity Control; Dehumidification/Humidification Required, In Percent (%); Response To Control Types - Liebert Himod Operation & Maintenance Manual

Dual Cooling Source
If dual cooling is available, the sensible cooling system operates in the same manner as a GLYCOOL
system, except that it is assumed that 100% chilled water capacity is available any time the chilled
water temperature is 3°F below the return air temperature. The control will not permit compressor
operation if the chilled water temperature is below the minimum chilled water temperature selected
through the SETUP OPERATION menu.
4.1.4

Heating Operation

Electric Reheat
The two heat stages are activated when the temperature control calculates a requirement of 50% and
100% respectively. Each stage is deactivated when the heat requirement is 25% less than the activa-
tion point.
4.2

Humidity Control

4.2.1

Dehumidification/Humidification Required, in Percent (%)

The humidity control program for the Advanced Microprocessor is based on a calculated % require-
ment for dehumidification/ humidification.
4.2.2

Response to Control Types

Proportional Control
The % requirement is determined only by the difference between the return air humidity and the
humidity setpoint. As the return air humidity rises above the humidity setpoint, the % dehumidifica-
tion required increases proportionally from 0 to 100% over a humidity band equal to the humidity
sensitivity setting. The converse is true for % humidification requirement.
4.2.3

Dehumidification Operation

1-Stage Dehumidification, Compressorized Direct Expansion (DX) Systems
Dehumidification with the standard configuration is accomplished by operating the compressor with
hot gas bypass active and the fan motors at low speed. If the installation has a very light sensible load,
dehumidification (low fan speed operation) will be inhibited at the point at which 125% heating would
be required to prevent overcooling. Dehumidification would be enabled when the temperature
increases to the point where only 50% heating is required.
GLYCOOL
On a system equipped with a GLYCOOL coil, dehumidification is accomplished with the compressor
only.
Dual Cooling
On a system equipped with an optional dual cooling fluid coil, assuming at least 50% chilled water
capacity is available and the minimum chilled water temperature is above its setpoint that is select-
able through the SETUP OPERATIONS menu, dehumidification is accomplished using the chilled
water coil and the compressor. If the chilled water temperature is below the minimum setpoint, the
compressor will not be permitted to operate.
4.2.4

Humidification Operation

System Activation
The humidifier is activated when the humidity control calculates a requirement of 100% humidifica-
tion, and deactivated when the requirement falls below 50%.
System Performance with Advanced Microprocessor Controls 29