There are several main components of a chilled water system: chillers, pumps, heat
exchangers, piping, and valves. The systems used to cool condenser water (e.g., a
cooling tower) are auxiliary to the chilled water system.
Chillers are central to the chilled water system design. Chillers contain a refrigerant
used to remove heat from the chilled water loop and a compressor to compress the
refrigerant. Proper sizing of chillers is determined by evaluating the peak load and
cooling load profile of the facility or process. Improper sizing of chillers can lead to
undersized units that are unable to cool equipment or oversized units that do not
Some facilities might require multiple chillers or cooling towers to meet equipment
cooling needs. In the case of multiple chillers or cooling towers, there might be
several options for the way in which the system is staged. For example, if multiple
cooling towers are installed, they could be plumbed in parallel to allow for condenser
water to pass through multiple cooling towers.
The efficiency of a chilled water system is dictated by its net useful refrigerating
effect, or its ability to remove heat, compared to the energy supplied to do so. A sys-
tem that removes more heat per unit of supplied energy is considered more efficient
than a comparable system.
There are no federal standards for the efficiency of a chilled water system; however,
the American Society of Heating, Refrigerating, and Air Conditioning Engineers
ASHRAE) ASHRAE 90.1-2007
Energy Standard for Buildings Except Low-Rise Residen-
has minimum required efficiencies for water chillers and is specified in
several local and state building codes.
Operation, Maintenance, and User Education
Because chilled water systems are complex systems, the efficiency of the system as a
whole is dependent upon the combined performance of each individual component.
Considering the interaction between components helps ensure optimum energy and
water savings from efficient operation and maintenance measures.
Prior to implementing any operation and maintenance efficiency measures, the
potential energy savings should be evaluated using the University of Massachusetts
Amherst Center for Energy Efficiency & Renewable Energy’s ChilledWater Systems
The tool was developed for facility personnel to evaluate potential
changes to existing chilled water systems and can be used to calculate the potential
energy-saving—and inherently water-saving—opportunities that exist from the
measures listed below. The maximum water efficiency can be reached by reducing
energy use, since it reduces the overall cooling load on the system.
American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE). 2007. ASHRAE 90.1-2007
Energy Standard for Buildings Except Low-Rise
U.S. Environmental Protection Agency (EPA) and U.S. Energy Department’s (DOE’s) ENERGY STAR.
Building Upgrade Manual, Chapter 9: Heating and Cooling Up-
University of Massachusetts Amherst, Center for Energy Efficiency & Renewable Energy (CEERE), Industrial Assessment Center (IAC). ChilledWater Systems Analy-
sis Tool (CWSAT).
DOE, Energy Efficiency & Renewable Energy (EERE). October 2005.
Improving Chilled Water System Performance: Chilled Water System Analysis Tool (CWSAT) Im-
Chilled Water Systems