McQuay MicroTech III RAH, Руководство по эксплуатации и обслуживанию, Страница: 110 / 122

110 McQuay OM 920-1
Operator’s Guide
A unit equipped with evaporative condensers can not operate in the cooling state below 40°F.
If the OAT Compressor Lockout Temperature on units with evaporative condensing is lowered
below 40°F, it will immediately be set back up to 40°F.
Freeze Protection Valve Control
When the Sump Temperature for Evaporative Condensing units gets too cold, the sump needs
to be emptied to prevent freezing. The Sump Dump output is used to control a Freeze
Protection Valve. This output is turned on if the sump temperature drops below the Freeze
Protection Setpoint, default = 35°F.
This output is turned back off if the sump temperature rises above this setpoint by more than
the Sump; Dump Differential, (default 3°F) and the unit is in the Mechanical Cooling State.
The requirement for Mechanical Cooling prevents the unit from continuously be emptied and
filled as the ambient temperature as measured by the sump temperature sensor varies below
35°F and above 38°F even when cooling was is not required.
If the unit is equipped with a Dolphin system and the pump does not run for five days, the
sump needs to be emptied. This would occur when cooling is not required and the OAT
remains below 35°F. Sump heaters are used to keep the sump temperature above 35°F when
the OAT drops below that value so an additional means of turning on the Freeze Protection
Valve is required. In addition to the requirement that the Sump Pump output be turned on to
open the valve when the sump temperature drops below 35°F, the Sump Pump output is to be
turned on if both of the following are true:
• Dolphin System= Yes
• The Sump Pump has been off for 120 hours or more
Heating Control
Entering Heating Operating State
The unit enters the Heating operating state from the Fan Only operating state when the control
temperature falls below the Zone Heating Set Point by more than half the Zone Heating Dead
Band. The unit transitions from heating to Fan only when the control temperature rises above
the Zone Heating Set Point by more than half the Zone Heating Dead Band. The unit will also
transition from the Heating to Fan only operating state if heating operation is disabled due to
OA ambient lockout.
Heating: Staged Zone Control
When the unit first enters the Heating operating state the unit goes directly to Stage # 1.
The number of Heating Stages increases when:
•
The time since the last stage change exceeds the Stage Time AND
•
Projected Control Temperature is less then the Zone Htg Spt (minus ½ the deadband). AND
• CtrlTemp is less than the Zone Htg Spt (minus ½ the deadband) AND
•
DAT is less than the Max DAT Htg Spt. AND
•
The current heating stage is less than the number of available stages
The number of Heating Stages decreases when:
• The time since the last stage change exceeds the Stage Time AND
• Projected Control Temperature is greater then the Zone Htg Spt (plus ½ the deadband) AND
• CtrlTemp is greater than the Zone Htg Spt (plus ½ the deadband) AND
• The current heating stage is greater than zero
OR
•
The time since the last stage change exceeds the Stage Time AND
• DAT is greater than the DATSpt AND