McQuay MicroTech III RAH Operation And Maintenance Manual page 116

Operator's Guide
116
When Ext mA is selected, the values "Min Htg Spt @" and "Max Htg Spt @" are entered as
mA values. When Ext VDC is selected, the values "Min Htg Spt @" and "Max Htg Spt @"
are entered as VDC values.
If Ext mA or Ext V is selected as the type of reset, the Min Htg Spt @ value may be set above
the Max Htg Spt @ value to cause a decrease in the DAT setpoint as the external signal or the
Min Htg Spt @ value may be set below the Max Htg Spt @ value to cause an increase in the
DAT setpoint as the external signal increase.
When ever the Clg Reset Type or Engineering Units is changed, the Min Clg Spt @ and Max
Clg Spt @ values revert to default values as follows:
• None: Min Clg Spt @=0NA, Max Clg Spt @=100NA
• Network: Min Clg Spt @=0NA, Max Clg Spt @=100NA
• Space, Return: Min Clg Spt @=73.0F, Max Clg Spt @=71.0F
• OAT: Min Clg Spt @=90.0F, Max Clg Spt @=70.0F
• ExtmA: Min Clg Spt @=4.0mA, Max Clg Spt @=20.0mA
• ExtVDC: Min Clg Spt @=0.0V, Max Clg Spt @=10.0V
An example of discharge temperature reset based on outdoor air temperature is illustrated in
Figure 13 (Cooling Reset Type Flag is set to "OAT" in this example). When the current
outdoor air temperature is greater than or equal to the Minimum Cooling Set Point Reset Value
(90°F in this example), the Discharge Cooling Set Point is set equal to the Minimum
Discharge Cooling Set Point (55°F in this example). This is shown as Point C in Figure 13.
When the current outdoor air temperature is less than or equal to the
Maximum Cooling Set Point Reset Value (70°F in this example), the Discharge Cooling Set
Point is set equal to the Maximum Discharge Cooling Set Point (65°F in this example). This is
shown as Point A in Figure 13. When the current outdoor air temperature is between the
Minimum Cooling Set Point Reset Value and the Maximum Cooling Set Point Reset Value,
the Discharge Cooling Set Point varies linearly between the Minimum Discharge Cooling Set
Point and Maximum Discharge Cooling Set Point. This is shown as Point B in Figure 13.
Figure 13: Discharge Temperature Reset Based on Temperature
McQuay OM 920-1