Perimeter Control

The perimeter is an additional heating source, independent from the ventilation system, for example, an underfloor heating. If configured in the VAV application, perimeter control does not require checking of the minimum airflow as it is not a part of the ventilation duct. The perimeter control in the auto mode is based on the heating demand from the space temperature control loop.

Perimeter Control According to HVAC Modes

Depending on the HVAC Mode settings (AirflowSetpointCalculator folder):

• Auto: working according to the heating demand,

• Heat: working according to the heating demand,

• Cool: switched off,

• MorningWarmUp: if the WarmUpHeater variable is set to true, the perimeter works according to the heating demand,

• PreCool: switched off,

• NightPurge: switched off,

• Off: switched off,

• Fire: switched off,

The perimeter can work in three modes defined in the ReheaterCommand variable:

• Auto: perimeter works based on the heating demand,

• Full Open: perimeter is set to the maximum control output, 100%,

• Full Close: perimeter is set to the minimum control output, 0%.

DualHeat

The DualHeat function for perimeter allows to meet energy efficiency requirements by allowing to select between two modes of heating. The DualHeat function is activated according to the setting of the HeatDamperPriority variable:

• primary stage (true): heater(s) works in the range of 0-50% (if DAT sensor is available: from the discharge air temperature heating loop with DAT setpoint based on the space temperature loop, or if DAT sensor is nor available: directly from the space temperature heating loop),

• secondary stage (false): damper in the range of 50-100% (directly from the space temperature heating loop).

The heaters priority is set in the HeaterPriority variable (PerimeterControl folder of the VAV application):

• HeaterPriority set to reheater:

  • primary mode: reheater in the range of 0-50% (indirectly from the discharge air temperature heating loop or directly from the space temperature heating loop),

  • secondary mode: perimeter in the range of 50-100% (directly from the space temperature heating loop);

• HeaterPriority set to perimeter:

  • primary mode: perimeter in the range of 0-50% (directly from the space temperature heating loop),

  • secondary mode: reheater in the range of 50-100% (indirectly from the discharge air temperature heating loop or directly from the space temperature heating loop);

• HeaterPriority set to simultaneous:

  • reheater and perimeter work in full range of the heating loop.

Perimeter Types

Depending on the configuration (see: Methods of Configuration), the perimeter can be controlled by the triac output (TO3) as follows:

• time-proportional (PWM) water perimeter with a valve and actuator, controlled by the TO3 output,

• water perimeter with a valve and actuator, on/off type, controlled by the TO3 output.

Regardless of the configuration of the control type, the perimeter is simultaneously controlled in analog mode by the AO2 output.

If the outside temperature signal is connected (from the BACnet/Modbus network), the perimeter is blocked over the setpoint in the MaxOatPerimeter variable (by default, 18°C/65°F).