McQuay MicroTech III RAH, Руководство по эксплуатации и обслуживанию, Страница: 115 / 122

McQuay OM 920-1 115
Operator’s Guide
The Application Discharge Air Temperature Setpoint is the Zone Heating setpoint if the
Control Temperature initiated the Special Start sequence. If the OAT initiated the Special Start
sequence, the setpoint is the Min DAT Limit for Zone units and the Eff DAT Clg Spt for DAT
units. The Temp Rise is the Maximum Temperature Rise of the Gas Heat Exchanger that is
entered at the factory for the specific unit.
After the modulating gas heating valve is set to the calculated position, there is a HeatUpDelay
(default = 60 second) to allow the heat exchanger to heat up. After this delay, since the unit is
100% Outside Air, the unit immediately transitions from Recirculation to the Fan Only state.
As soon as the unit enters the Fan Only state, the unit will immediately transition to either the
Heating state or the MinDAT state.
The unit remains in either Heating or Minimum DAT Control for the duration of the
LowFireTime (Default = 240 seconds). The gas heating valve does not modulate from its
calculated value to allow the temperature to approach equilibrium with modulating gas heating
valve at a fixed position.
The unit reverts to normal modulation of the gas heating valve when the LowFireTime has
elapsed since the unit entered Heating or MinDAT.
SCR Electric Heat Control
When the Heating type is configured for SCR Electric and the unit is in the Heating or
MinDAT operating state, a PI loop is used to modulate a heating capacity output (EMB-X7) to
maintain the discharge air temperature at the discharge air heating setpoint. Digital outputs
(EMB-DO1 and EMB-DO2) are enabled on a call for heat while the analog output (EMB-X7)
is used to modulate the signal between 0 and 100% capacity.
Return Air Units
When the unit enters the Heating operating state, the controller first holds the gas valve at the
minimum fire position (5% or 33% depending on the burner model) until the Heating
Interstage Timer expires. Then, the controller modulates the gas valve to maintain the
discharge air temperature at the Discharge Heating Set Point.
Discharge Air Temperature Setpoint Reset - Heating
The Heating DAT Setpoint may be reset for units with DAT Heating Control. The Discharge
Air Temperature Setpoint will never be set below the Minimum DAT Heating Setpoint or
above the Maximum DAT heating Setpoint on the Heating Reset menu. The reset type may be
set to one of the following:
•
None Discharge Heating Spt = User Adjustable
• Network Discharge Heating Spt = Network DAT Htg Setpoint (NetDAClSP) when it is valid
•
Space Discharge Heating Spt is based on the Space Sensor
•
Return Discharge Heating Spt is based on the Return Air Sensor
• OAT Discharge Heating Spt is based on the Outdoor Air Temperature
•
Ext mA Discharge Heating Spt is determined by a 0-20 or 4-20 mA signal
•
Ext V Discharge Heating Spt is determined by a 0-10 or 2 - 10 VDC signal
Reset reverts from Return to None when a Return Air Sensor opens or shorts. Reset reverts
from Space to None when a Space Sensor opens or shorts. Reset reverts from OAT to None
when an Outdoor Air Sensor opens or shorts.
When Space, Return, OAT, Ext mA, or Ext V is selected, the Discharge Heating Spt equals the
Max Htg Spt when the selected value equals the Max Htg Spt @ value. Similarly, the
Discharge Heating Spt equals the Min Htg Spt when the selected value equals the Min Htg Spt
@ value.
When Space, Return, or OAT is selected, it only makes sense for the DAT Heating setpoint to
decrease as the selected temperature increases as shown in the graph below.