5.11 Primary Cooling Systems
Chillers. Chillers shall be specified in accordance with the
latest Air-conditioning and Refrigeration Institute (ARI)
ratings procedures and latest edition of the ASHRAE
Standard 90.1. As a part of the life cycle cost analysis, the
The primary cooling system includes chillers, chilled
use of high-efficiency chillers with COP and IPLV ratings
water and condenser water pumps, cooling towers, piping
that exceed 6.4 (0.55 kW/ton) shall be analyzed. Likewise,
and piping specialties. The chilled water systems shall
the feasibility of gas-engine driven chillers, ice storage
have a temperature differential between 5.5C and 6.7C
chillers, and absorption chillers shall be considered for
(10F and 12F) for HVAC systems that primarily use fan
demand shedding and thermal balancing of the total
coil units. For HVAC systems that primarily use air-
system.
handling units, the temperature differential shall be
between 6.7C and 8.9C (12F and 16F). The chilled
BACnet or LONWORKS Microprocessor-based controls
water system shall have a design supply water temperature
shall be used. Chiller staging controls shall be capable of
between 4.4C and 7.2C (40F and 45F). In climates
DDC communication to the central building Energy
with low relative humidity, a 7.8C (46F) may be used.
Management System. The control panel shall have self-
diagnostic capability, integral safety control and setpoint
District Chilled Water
display, such as run time, operating parameters, electrical
low voltage and loss of phase protection, current and
GSA buildings are built for the long-term; therefore, it
demand limiting, and output/input-COP [input/output
is prudent for GSA to provide the building chilled water
(kW/ton)] information.
system. District chilled water, if available, may be
considered for cooling only if it is determined to have
When the peak cooling load is 1760 kW (500 tons) or
long-term reliability and can be economically justified
more, a minimum of three chilled water machines shall be
through a life cycle cost analysis. In the event District
provided. The three units shall have a combined capacity
chilled water is utilized, appropriate space must be
of 120 percent of the total peak cooling load with load
provided to allow GSA to install chillers, cooling towers,
split percentages 40-40-40 or 50-50-20. If the peak
and associated equipment, at a later date. If chilled water
cooling load is less than 1760 kW (500 tons), a minimum
is furnished to the building, such as under a district
of two equally sized machines at 67 percent of the peak
chilled water plan, it shall be used in conjunction with
capacity (each) shall be provided. All units shall have
a heat exchanger in the mechanical room near the
adequate valving to provide isolation of the off-line unit
entrance into the building.
without interruption of service. Cooling systems with a
refrigeration capacity less than 176 kW (50 tons) shall use
air-cooled chillers.
Chilled Water Systems
Chillers shall be piped to a common chilled water header
Mechanical equipment rooms must be designed in
with provisions to sequence chillers on-line to match the
accordance with the requirements of ASHRAE Standard
load requirements. All required auxiliaries for the chiller
15: Safety Code for Mechanical Refrigeration. Chiller leak
systems shall be provided with expansion tanks, heat
detection and remote alarming shall be connected to the
exchangers, water treatment and air separators, as
BAS.
144 F A C I L I T I E S S T A N D A R D S
FOR THE
PUBLIC
BUILDINGS
SERVICE
5.11 Primary Cooling Systems
Revised March 2005 PBS-P100
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