User Manual

Unrestricted 0 – Siemens Smart infrastructure Page 29
temperature very quickly. Based on the measured room temperature, the room temperature
controller must calculate a setpoint for the supply air temperature at the discharge air outlet.
When the room needs cooling, the supply air damper must control the supply air between
min. and max. cooling to maintain the room temperature at the cooling setpoint. The room
temperature must be acquired via a sensor located in the room unit or an extract air sensor in
the duct. The described operating conditions define the various operating modes.
Air quality (combined CO
2/VOC) control
The room sensor measures the higher value of the CO
2/VOC concentration. If the measured
quality of the indoor air is below the set CO
2/VOC limit, the air quality controller operates at
Vmin. If the measured air quality exceeds the CO
2/VOC limit, the volume setpoint will be
increased up to Vmax (for a preset value of CO
2/VOC max). Vmin must be determined by the
lower of the two setpoints for heating and cooling, and Vmax by the higher of the
two setpoints.
Heating valve control (optional)
Sequential control of variable damper and reheating valve is required to achieve the room
temperature heating setpoint. When the room temperature drops below the heating setpoint,
the reheating coil valve must be opened and the variable air volume (VAV) damper must be
controlled to a position that provides the minimum air volume. After the reheating coil valve
is fully open, the variable air volume (VAV) damper must control the supply air between min.
and max. heating to maintain the room temperature at the heating setpoint.
Cooling valve control (optional)
Sequential control of variable damper and re-cooling valve is required to achieve the room
temperature cooling setpoint. When the room temperature exceeds the cooling setpoint, the
cooling coil valve must be opened and the variable air volume (VAV) damper must be
controlled to a position that provides the minimum air volume. After the cooling coil valve is
fully open, the variable air volume (VAV) damper must control the supply air between min.
and max. cooling to maintain the room temperature at the cooling setpoint.
Extract air volume control – room pressure control (optional)
Negative or positive room air pressure control must be accomplished by flow synchronization
(air flow tracking). The extract air volume must be controlled to track the supply air volume
to maintain the required offset between supply and extract air needed to achieve the required
pressure. The extract air volume setpoint must be calculated to maintain either a fixed or
a ratio air volume offset between supply and extract air. The extract air setpoint must vary
as the supply air in accordance with the present operating mode.