When the building control system is used to provide this signal, outdoor air temperature, cooling coil valve output, or other parameters may be used to initiate bridge operation/shutdown. Designer shall specify parameter to be used. Bridge modes of operation will be controlled by chilled water based on the bridge enable signal from the BAS.
- Chilled Water Pump VFD(s) (Pumps to be provided by contractor)
- TCV-A(B) Valve(s) including actuator
- RTDs for Supply and Return Temperature
- Thermowells for RTDs
- Flow Meter
- Differential Pressure Transmitter (Utility – if needed; connection points for this DPT are required)
- Differential Pressure Transmitter (End of Line)
- Chilled Water Bridge Controller
- Control Panel for Bridge Controller
- No penetrations are allowed in the top of the panel box. All penetrations must be made with liquid tight connectors.
- The 120VAC power to the panel must be on its own designated breaker and have nothing else tapped off it. No junction boxes are allowed in the conduit run to ensure that no other circuits can be tapped off it. A pulling “C” may be used instead of a junction box to assist in wire pulling or if maximum number of bends in conduit has been reached.
Unless otherwise as required by the VFD manufacturer, the motor drive output wiring from the VFD shall be properly sized XHHW-2 run in grounded metallic conduit. The use of specific “VFD Cable” is generally not required. No top entry allowed.
Preferred valve orientation is with the shaft in the horizontal plane. When mounted in the horizontal plane, the actuator assembly must not be located at the bottom of the pipe. The position indicator must be visible from the ME room floor. There must have sufficient clearance to remove the actuator assembly from the valve. Slip-on flanges shall not be used for control valve installation and can only be used if approved for installation by UNC Chilled Water Director.
- RTU (Return Temperature Utility) must be installed a minimum of 7 pipe diameters downstream of the last connected tee. The thermowell must be installed in the same plane or above the tee and upstream of the control valve to avoid cold trap.
- STU (Supply Temperature Utility) must be installed a minimum of 3 pipe diameters from pipe fittings.
Glass thermometer: Thermometer shall be an industrial glass thermometer with cast aluminum body and have a 9” scale. The scale will be from 30º to 120ºF degree scale with 2ºF degree division. The thermometer shall have a 3 ½” stem and variable degree angle adjustment and union connection.
Solar thermometer: Thermometer shall be an industrial solar powered thermometer capable of reading a temperature range 30º to 120ºF with an accuracy of +/- 2%.
The End of Line Differential Pressure Transmitter (PDT-1) shall be installed at the worst location in the system from a pressure standpoint. This is typically near the most remote air handler, or the air handler located on the highest floor of the building. Contact the Chilled Water Engineer for assistance in determining the appropriate location.
The Utility Differential Pressure Transmitter (PDT-2) shall be located just inside the bridge isolation valves, as close as possible to the location that the chilled water pipes enter the building. The Chilled Water Engineer can assist with this placement as well.
RTD Temperature Sensors: Charlotte Wire and Cable no. CW09306 (or equivalent approved by Chilled Water), 3-conductor, stranded, twisted, 18-gauge, foil shield with drain wire, Stranded, Tinned Copper, PVC jacket, 300Volt rating.
No bridge wiring conduits will be shared with any other system.
Power wiring shall be in one dedicated conduit with no junction boxes. Pulling “C” and/or “LB” only.
All wiring in conduits shall be continuous wire runs with no splices. No junction boxes are allowed. Only pulling “C” and “LB”.
If there are any transitions from EMT to flexible conduit, that flexible conduit MUST be liquid-tight metallic conduit.