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SYS-APM001-EN Chiller System Design and Control 25
Guidelines for system efficiency monitoring
ASHRAE Guideline 22 Instrumentation for Monitoring Central Chilled-Water
Plant Efficiency
6
was first published in June 2008. It states:
Guideline 22 was developed by ASHRAE to provide a source of
information on the instrumentation and collection of data needed for
monitoring the efficiency of an electric-motor-driven central chilled-
water plant. A minimum level of instrumentation quality is
established to ensure that the calculated results of chilled-water
plant efficiency are reasonable. Several levels of instrumentation are
developed so that the user of this guideline can select that level that
suits the needs of each installation.
The basic purpose served by this guideline is to enable the user to
continuously monitor chilled-water plant efficiency in order to aid in
the operation and improvement of that particular chilled-water plant,
not to establish a level of efficiency for all chilled-water plants.
Therefore, the effort here is to improve individual plant efficiencies
and not to establish an absolute efficiency that would serve as a
minimum standard for all chilled-water plants.
Guideline 22 includes a discussion of:
• types of sensors and data measurement devices
•calibration
• measurement resolution, accuracy, and uncertainty
• calculation methods
• example specification
• examples of measured long-term performance
Guideline 22 recommends tracking and archiving the following over the life
of the plant, in addition to normal equipment operating trends. The ability to
obtain this information is dependent on the instrumentation and data
measurement capabilities of the system.
1 Average day’s outdoor air temperature (obtain the outside air
temperature every 30 minutes and find the average of these samples each
day)
2 Day’s high temperature
3 Day’s low temperature
4 Day’s high wet-bulb temperature (calculate from temperature and
enthalpy)
5 Chilled-water supply temperature (average, max and min if chilled-water
temperature is not fixed)
6 Total ton-hours (kWh) production of chilled water for the day
7 Total kWh power input for each component for the day
8 Average kW/ton (COP) for the plant for the day
For a copy of ASHRAE Guideline 22 and
other ASHRAE publications, visit the
ASHRAE bookstore at www.ashrae.org/
bookstore.