Specifications - City of Montpelier, Vermont

Title:Montpelier District HeatingCity of Montpelier, VT15910 – Sequences of OperationsIssue Date:September 28, 2012Page #:3 of 11c. When the controls command space heating on, the lead pumps (P1/P2 and P2.1/P2.2) shall engage.d. P1 and P2 are both constant speed pumps and flow water throughthe boiler room’s loop and the City Hall building.3. Time of Day Controla. The existing time of day controls on heating terminals willcontinue to work as it did before this project began.4. Building Hot Water Control – Normal Conditionsa. The controls shall adjust the speed of P2.1/P2.2 to maintain thesetpoint at TT1.4 (main header hot water supply).b. The setpoint at TT1.4 shall follow this adjustable outdoor air resetschedule (linear relation between outdoor air temperature and hotwater temperature:1.) Outdoor air temperature 50 degrees F: Hot watertemperature 140 degrees Fc. Boilers B1 and B2 and their associated pumps shall be off.d. The existing controls (unaffected by this project) for the firedepartment pumps, mixing valve and snowmelt systems shallremain asis. The current operation includes manual engagement ofthe Fire Department heating pump and an inpiping controller forthe Fire Department’s mixing valve. The snowmelt system’scontroller is in the Fire Department basement.e. The controls will position the twoway valve in the district heatsystem to maintain a leaving hot water setpoint of 168 degrees F(adjustable).5. Building Hot Water Control – District Heat Failurea. If the controls and district heating system are unable to maintainthe water temperature at TT1.4 with 5 degrees of the setpoint formore than 30 minutes or 10 degrees for 5 minutes, the controlsshall signal an alarm at the HMI and engage the lead boiler, boilerpump and shunt pump.b. The system shall stage the boiler between low, high and off tomaintain the setpoint at TT1.4. During this operation the controlsshall keep both boiler pumps engaged continuously.c. During this time, the controls shall keep shutdown the district heatexchanger and pump system and keep the control valve in the loopclosed. This is important to be certain the City Hall boilers are notproviding heat to the failed district heating system at the expenseof City Hall.SEQUENCE OF OPERATION159103