McQuay MicroTech III RAH, Руководство по эксплуатации и обслуживанию, Страница: 111 / 122

McQuay OM 920-1 111
Operator’s Guide
•
The current heating stage is greater than zero
OR
• The current heating stage is more than the number of available heating stages.
Heating DAT Staging or MinDAT Staging
When the unit enters the Heating or Minimum DAT states and all heating is off, the unit goes
directly to Heating Stage # 1 so that the first stage of heat is turned on immediately.
The number of Heating Stages increases when either of the following combinations is true:
• The current heating stage equals zero AND
• DAT is less than the effective DAT setpoint (DAT staging) or the MIN DAT limit (MinDAT
staging) by ½ the deadband
OR
•
The time since the last stage change exceeds the Htg Stage Time AND
•
The current heating stage is less than the number of available stages AND
•
DAT is less than the effective DAT setpoint (DAT staging) or the MIN DAT limit (MinDAT
staging) by ½ the deadband
The number of Heating Stages decreases when either of the following set of conditions is
True:
• The time since the last stage change exceeds the Htg Stage Time. AND
• The current heating stage is greater than zero AND
• DAT is greater than the effective DAT setpoint (DAT staging) or the MIN DAT limit
(MinDAT staging) by ½ the deadband
OR
•
The current heating stage is more than the number of available heating stages
The unit enters the Min DAT operating state during occupied operation when neither cooling
nor heating is required based on the unit heat/cool changeover function but the discharge air
temperature falls below a minimum discharge temperature limit by more than ½ the deadband.
The Min DAT operating state prevents cold discharge air temperatures during what would
normally be the Fan Only operating state.
Modulating
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. When the unit is in the Heating operating state, heating capacity is
modulated to maintain the discharge air temperature at the Discharge Heating Set Point.
There are several different modulating heating types available with this equipment. There are
some differences in the control sequence depending on the heat type installed. The different
types are described in the following sections.
Steam or Hot Water Heat: Face and Bypass Damper Control
When a unit is equipped with steam or hot water with face and bypass damper heating there
are two different methods used for controlling the heating arrangement. These are the “Open
Valve” and “Modulating Valve” methods and are described in the following sections. The
parameter is adjustable via the following path: Extended Menus/Heating Setup/F&BP
Method.