Specifications - City of Montpelier, Vermont

Montpelier District HeatingCity of Montpelier, VTIssue Date:September 28, 2012Title:15900 – Direct Digital Control SystemPage #:27 of 40a. Size operators for smooth and positive operation of devices served, andwith sufficient capacity to provide tight shutoff against systemtemperatures and pressure encountered. Use rolling diaphragm, pistontype operators with adjustable stops. Equip operators with spring returnfor applications involving fire, freeze protection, moisture protection orspecified normally open/closed operation.b. Provide operators and pilot positioners with linkages and brackets formounting on device served.2. Electronic Valve Actuatorsa. Each actuator shall have current limiting circuitry incorporated in itsdesign to prevent damage to the actuator.b. Provide modulating and twoposition actuators as required by thesequence of operation. Actuators shall provide the minimum torquerequired for proper valve closeoff against the system pressure for therequired application. Size valve actuator based on valve manufacturer’srecommendations for flow and pressure differential. The spring returnfeature shall permit normally open or normally closed positions of thevalves as required. All direct shaft mount rotational actuators shall haveexternal adjustable stops to limit the travel in either direction.c. Provide valve actuators to fail in the last position for valves in the districtheating system.d. Provide valve actuators to springreturn (fail) open for inbuildingheating equipment.e. Modulating Actuators shall accept 24 VAC or VDC and 120 VAC powersupply and be UL listed. Control signal shall be 210 VDC or 420 mAand actuator shall provide a clamp position feedback signal of 210VDC. Feedback signal shall be independent of the input signal and maybe used to parallel other actuators and provide true position indication.The feedback signal of each valve actuator (except terminal valves) shallbe wired back to a terminal strip in the control panel for troubleshootingpurposes.f. Twoposition or open/closed actuators shall accept 24 or 120 VACpower supply and be UL listed. Butterfly isolation and other valves asspecified in the sequence of operations shall be furnished with adjustableend switches to indicate open/closed position or be hard wired tostart/stop associated pump or chiller.g. Electronic valve actuators shall be Belimo or equivalent.K. Control Dampers1. GeneralDIRECT DIGITAL CONTROL SYSTEMS1597227