Specifications - City of Montpelier, Vermont

Title:Montpelier District HeatingCity of Montpelier, VT15910 – Sequences of OperationsIssue Date:September 28, 2012Page #:6 of 111. The Police Station controls for all existing items will remain unchanged inthis project, save the building hot water temperature control.B. Winter Operation:1. The controls shall adjust a 3way mixing valve in the building’s hot watersystem to match the existing boilerbased operation.2. The existing hot water pump shall operate as it does under the boiler basedoperation.3. The controls shall adjust the control valve in the district heating line tomaintain a 168 degree F return water temperature to the district system.C. NonWinter Operation: The existing building control will position motorized 3way valves to the summer position and operate the cooling equipment. Thisproject will make no changes to that system or operation.D. District Heat Failure: If the district heating equipment cannot maintain hot watertemperature within 5 degrees F (adjustable) of setpoint for one hour (adjustable)the controls shall signal an alarm at the HMI. The human operators will lineupmanual valves to allow the existing boiler and existing pumps and command thecontrol system to operate with the boiler as it before this project’simplementation. After the district heating is restored, human operators will line upvalves to use district heat and command the control system to operate in thedistrict heat mode.E. Domestic Hot Water: The existing domestic hot water system includes a controlthat stages a pump on/off to bring boiler water through an indirecttype waterheater. This project includes no changes to that control (winter and nonwintertimes).3.3 Union ElementaryA. Hot Water System – Winter Operation1. The operator shall select the lead hot water pump (P3/P4) for thebuilding hot water system in the HMI.2. When the outdoor air temperature is below 50 degrees F (adjustable) forone hour (adjustable) the controls shall enable the hot water system:a. The controls shall start the lead hot water pump (P3/P4):1.) The controls shall continuously measure the zonedifferential pressure transmitters and compare theirmeasured values with the setpoint (10.0 psig, adjustable)and select the zone with the greatest error between setpointand measured value.2.) The controls shall adjust the l lead hot water pump’s speedto satisfy the most critical zone differential pressure.3.) If the lead pump fails, the controls shall signal an alarm atthe HMI and switch to the standby pump and operate it asdescribed above.SEQUENCE OF OPERATION159106