06-06
the operating controls to meet the intent of the system design.
The operating controls shall be selected by the designer to suit
the system capacity and configuration. The following guidelines
are offered:
a. Single Chiller Installation: With a single chiller, the
capacity control shall be generally based on monitoring the
return chilled water temperature and/or maintaining variable
fixed leaving chilled water temperature.
b. Two Chillers Installation: With two chillers, primary/secondary
pumping arrangement shall be used with variable speed drives
for the secondary pumps, if the pumps are 5.5 kW (7.5 HP) and
larger. For smaller secondary pumps, the capacity reduction of
the chillers shall be affected without the use of the variable
speed drives for the secondary pumps.
2. Miscellaneous Controls:
a. Load Reduction: For the peak demand shaving, consideration
shall be given to unloading the chillers through the ECC
software.
b. Chilled Water Reset: The chilled water leaving temperature can
be changed in response to the outdoor temperature on a reset
schedule and this control can be used with or without the flow
control for the chiller operation.
5.3 DIRECT EXPANSION SYSTEMS
Depending upon the configuration of the building, and available space,
the following arrangements shall be evaluated:
A. ROOF TOP UNITS: Penthouse type of fully weatherized roof top package
units in modular sections and complete with air and refrigeration
systems.
B. REMOTE UNITS: Conventional horizontal, or vertical, draw-through
indoor, DX air handling units with remote, air cooled, or water
cooled, condensing units.
C. PACKAGE UNITS: Single, or multiple, commercial grade package units
with air cooled, or water cooled, refrigeration condensers.
D. HEAT PUMPS: The use of the closed loop, water cooled, incremental,
heat pump system shall be evaluated for mild climate locations and
for the buildings with relatively large interior area. The heat
rejected by the interior spaces (which require cooling year round)
shall be the primary source of heating with steam to hot water, or
electric resistance heat, as back up.
5.4 CHILLED WATER SYSTEM
See supplement, ATTACHMENT NO. 2.
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