Specifications - City of Montpelier, Vermont

Title:Montpelier District HeatingCity of Montpelier, VT15910 – Sequences of OperationsIssue Date:September 28, 2012Page #:4 of 11d. The boiler’s existing, onboard temperature limit control will keepthe water temperature within the boiler below the maximumallowed. The existing, onboard highlimit safety will remain inplace.e. When the district heat system failure is resolved, operating staffwill have to reset the building heating mode at the HMI back todistrict heat. This reset will disable the boiler(s) and associatedpumps restore the operation of the district heating pump andcontrol valve.6. Fire Department Hot Water Controla. The existing control system for starting the hot water pumps andpositioning the 3way mixing valve shall operate as they did beforethis project’s work.B. Winter Operation, Demand Limiting1. If the Main Plant controls call for demand limiting via a discrete point inthe City Hall Control Panel, the City Hall controls will enable the demandlimiting control.2. The controls will disable the heat exchangers and P2.1 and P2.2 systemand engage the lead boiler and associated pumps. The controls will closethe control valve in the district heat system.3. The controls will operate the burner between off, low and high to maintainthe water temperature at TT1.4 at the setpoint (determined by the outdoorair reset schedule described above).4. If one boiler is inadequate to maintain the water temperature at TT1.4, thecontrols shall engage the lag boiler and operate its burner to maintain thesetpoint at TT1.4.5. The controls shall disable the lag boiler and associated pumps if there isno need for its operation for a onehour (adjustable) period.C. NonWinter Operation, District Heat Source1. During nonheating times, the City Hall plant will be the source of heat forthe district. City staff will command the Main Plant controls to summermode. The Main Plant will signal the City Hall controls to become theheating source for the district. The Main Plant controls will transmit ananalog signal to the City Hall controls for district heat pump speed control.2. The human operator will clean all strainers in City Hall before reversingthe flow, at the start and end of the nonwinter operation.3. The human operator will define the lead/lag status for these components:a. Boiler 1/Boiler 2 (and associated pumps)b. District heating pump P1.1/P1.2c. Building heating pumps (serving as headercirculation pumps innonwinter times) P1/P2SEQUENCE OF OPERATION159104