Specifications - City of Montpelier, Vermont

Montpelier District HeatingCity of Montpelier, VTIssue Date:September 28, 2012Title:15900 – Direct Digital Control SystemPage #:25 of 401.) Setpoint reset slide switch providing an adjustable range.2.) Momentary override request push button for activation of afterhours operation.3.) Analog thermometer (exception: where not available for someapplications).3. Duct Mount Sensorsa. Duct mount sensors shall mount in an electrical box through a hole in theduct and be positioned so as to be easily accessible for repair orreplacement.b. Duct sensors shall be insertion type and constructed as a completeassembly including lock nut and mounting plate.c. For outdoor air duct applications, use a weatherproof mounting box withweatherproof cover and gasket.4. Averaging Sensorsa. For ductwork greater in any dimension that 48 inches and/or airtemperature stratification exists, utilize an averaging sensor withmultiple sensing points, when physically possible.b. For plenum applications such as mixed air temperature measurements,utilize a string of sensors mounted across the plenum to account forstratification and/or air turbulence. The averaging string shall have aminimum of 4 sensing points per 12 foot long segment.c. Provide supports at the sides of the duct to support the capillary sensingstring.H. Output Devices General1. Fail Safe Operation:a. Design and install control valves and dampers to fail safe in either thenormally open or normally closed position as required for freeze,moisture, smoke or fire protection.b. Spring Ranges: Provide range as required for system sequencing and toprovide tight closeoff.1.) Power Operated Control Dampers (other than VAV Boxes):Provide factory fabricated, balanced type dampers.I. Damper Actuators1. Generala. 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.DIRECT DIGITAL CONTROL SYSTEMS1597225