18 August 1998
(1) All Modes. The UMCS will start and stop the distribution pump based on the signal from an
outside-air temperature sensor as shown. The UMCS will enable control of the hot water boiler bypass
valve when pump is operating and the system is in heating mode. When the system is not in heating
mode the boiler bypass valve will be disabled. The UMCS will enable control of the air-cooled chiller
when the distribution pump is operating and the system is in cooling mode. Heating and cooling modes
will be initiated by the UMCS and confirmed by monitoring the position of the changeover valves. UMCS
will not make the heating to cooling changeover until the return water temperature drops below 90
degrees F and will not make the cooling to heating changeover until the return water temperature rises
above 60 degrees F.
(2) Heating Mode. When the heating mode is selected, the system changeover valves will
close to the chilled water flow and will open to flow through the hot water boiler. The UMCS will enable
local control of the hot water boiler. The UMCS will control the hot water supply temperature by
modulating the hot water boiler bypass valve in response to a temperature sensor located in the hot water
supply line to maintain its setpoint. The UMCS will reset the hot water supply temperature setpoint with
respect to the outside air temperature in a linear schedule as shown. Reduced-flow control of the hot
water bypass valve will be coordinated with the boiler manufacturer's recommendations and boiler safety
settings. The UMCS will disable boiler operation when the distribution pump is off. The UMCS shall reset
the hot water supply temperature setpoint with respect to outside air temperature in a linear schedule as
(3) Cooling Mode. When the cooling mode is selected, the hot water boiler bypass valve will be
closed to the boiler, the system changeover valves will close to the hot water flow and open to the chilled
water flow. The UMCS will enable local control of the air-cooled chiller and condenser. Chilled water
supply temperature will remain under local controls. When the distribution pump is not operating the air-
cooled chiller local controls will be disabled.
h. Water-Cooled Chiller System Sequence of Operation (Figure 8-8 and Table 8-8).
(1) All Modes. The UMCS will enable and disable the chiller plant operation based on
occupancy schedule, heating/cooling operation, and outside air temperature. When the chiller is stopped,
the chilled water and condenser water pumps shall have delayed shutdown after compressor shutdown.
(2) Chiller Control. The UMCS will first start the chilled water pump and the condenser water
pump. The chiller local control interlocks will operate the chiller to maintain a constant chilled water
supply temperature after flow has been established. The UMCS will reset the chiller's local control chilled
water supply temperature setpoint based on the chilled water temperature as shown.
(3) Cooling Tower Control. The UMCS will start/stop the cooling tower fan, modulate the
condenser water bypass control valve, and select the fan speed as required to maintain condenser water
supply temperature setpoint. When the chiller is stopped, the chilled water and condenser water pumps
will have delayed shutdown after compressor shutdown.
i. Multizone Air Handling System with Hot Water and Chilled Water Coils Sequence of Operation
Outside-Air, Return-Air, and Relief-Air Dampers.
(a) Occupied Mode. The minimum outside air damper will open. The maximum outside-
air, return-air, and relief-air dampers will be modulated under mixed-air temperature and economizer
Unoccupied Mode. The dampers will return to their normal positions as shown.
Supply-Fan and Return-Fan Control.