5.21 Control Systems

Automatic Temperature and Humidity Controls
A direct digital control (DDC) system with host computer controlled monitoring and control shall be provided.

Control Systems shall be BACnet or LONWORKS, conforming to ASHRAE BACnet Standard 135.

Controls. Pre-programmed stand-alone single or multiple loop microprocessor PID controllers shall be used to control all HVAC and plumbing subsystems.

PID loops shall be utilized. All chillers, boilers, terminal units and air handling units shall have self-contained BACnet or LONWORKS controllers, capable of communicating with the Building Automation System.

Temperature Controls. Heating and cooling energy in each zone shall be controlled by a thermostat or temperature sensor located in that zone. Independent perimeter systems must have at least one thermostat or temperature sensor for each perimeter zone.

A 1.5°C (3.5°F) dead band shall be used between independent heating and cooling operations within the same zone.

Night set-back and set-up controls must be provided for all comfort conditioned spaces, even if initial building occupancy plans are for 24-hour operation. Morning warm-up or cool-down must be part of the control system. Controls for the various operating conditions must include maintaining pressurization requirements.

Humidity Controls. Indoor and outdoor humidity sensors shall be calibrated in-place during system startup and at least annually thereafter. Dew point control is preferred because it tends to provide more stable humidity levels. However, rh sensors are acceptable, provided they have been calibrated in-place, and provided that they have co-located with dry bulb sensors so that the BAS can convert these two signals to a dew point value for control purposes.

Temperature Reset ControlsAir Systems. Systems supplying heated or cooled air to multiple zones must include controls that automatically reset supply air temperature required by building loads or by outside air temperature.

Hydronic Systems. Systems supplying heated and/or chilled water to comfort conditioning systems must also include controls that automatically reset supply water temperatures required by temperature changes responding to changes in building loads (including return water temperature) or by outside air temperature.

Last Reviewed: 2019-02-26