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System Performance Microprocessor Controls
Liebert
®
Mini-Mate2
™
50
7.0 SYSTEM PERFORMANCE MICROPROCESSOR CONTROLS
This section describes in detail how the Mini-Mate2 responds to operator inputs and room conditions.
7.1 Temperature Control
7.1.1 Cooling/Heating Required
The temperature control program for the microprocessor is based on a calculated percentage
requirement for cooling/heating.
7.1.2 Cooling Operation (Compressorized Direct Expansion and Chilled Water)
Cooling is ACTIVATED when the temperature control calculates a requirement for cooling of 100%. It
is DEACTIVATED when the cooling requirement drops below 50%. Hot gas bypass is energized on
DX units when a call for cooling occurs unless there is also a call for dehumidification.
7.1.3 Heating Operation
Electric Heat or Hot Water
The reheat stage is ACTIVATED when the temperature control calculates a requirement of 100%.
Conversely, the reheat is DEACTIVATED when the heat requirement is 50% less than the activation
point.
SCR Electric Reheat
The SCR (Silicon Controlled Rectifier) controller proportionally controls the stainless steel reheat
feature to maintain the selected room temperature. The rapid cycling made possible by the SCR
controller provides precise temperature control, while the constant element temperature improves
heater life. During operation of the SCR control, THE COMPRESSOR OPERATES
CONTINUOUSLY. The heaters are modulated to provide temperature control. The display status
will show when the unit is cooling and heating. The control will automatically lock the compressor
cooling to “ON” position, except when the temperature falls below the low temperature alarm set
point. Cooling will then be disabled until the room temperature reaches the temperature set point.
7.2 Humidity Control
7.2.1 Dehumidification/Humidification Required
The humidity control is based on a calculated percentage requirement for dehumidification or
humidification (i.e., the difference between the return air humidity and the humidity set point). As
the return air humidity rises above the humidity set point, the percent dehumidification required
increases proportionally from 0 to 100% over a humidity band equal to the humidity sensitivity
setting. The converse is true for percent humidification requirement.
7.2.2 Dehumidification Operation, Compressorized Direct Expansion (DX) Systems
Dehumidification with the standard configuration is accomplished by operating the compressor
without the hot gas bypass active. Dehumidification will be disabled if the heating requirement
exceeds 125%. It is re-enabled when the heating requirement reaches 50%.
Table 22 Cooling and dehumidification load response of hot gas bypass
Situation Hot Gas Bypass
Cooling only ON
Dehumidification only OFF
Cooling with
Dehumidification
OFF