ASHRAE Journal - June 2014 - 35

Column EnginEEr's notEbook

type applications, m is typically in the range
-0.2 to 0.
* Disable the waterside economizer if it is not reducing the chilled water return temperature by at least 1°F
(0.6°C).
* Disable chillers when HXLWT is at or below the desired chilled water supply temperature setpoint.
* Enable chillers when chilled water supply temperature is greater than desired setpoint. Note that multiple
chillers may need to be enabled if the current chilled water flow is well above the design flow of a single chiller.
* Run as many tower cells as tower minimum flow
limits will allow.
* Control condenser water flow to roughly match the
current chilled water flow but reduce flow (within tower minimum flow constraints) as needed to maintain a
minimum 5°F (2.8°C) range. The lower flow and higher
range improves tower efficiency and reduces pump power. Flow can be controlled by staging pumps, modulating speed on variable speed pumps, and/or modulating
isolation valves on the heat exchanger. Flow rate can be

measured directly with a flow meter (full bore magnetic
or ultrasonic type are recommended to prevent fouling)
or deduced from heat exchanger pressure drop.
* Tower speed control:
1. When waterside economizer is disabled: Control
speed to maintain normal condenser water temperatures which should be reset from load or wet-bulb temperature.9
2. When waterside economizer and chillers are enabled: Run tower fans at 100% speed.
3. When chillers are disabled: Control speed to
maintain HXLWT at desired chilled water supply temperature setpoint.
The only complex sequence above is predicting when
the economizer should be enabled. Fortunately, if the
prediction calculation is off and the economizer is
enabled prematurely, it will shortly be disabled and
the plant will see no disruptions in chilled water flow
or supply temperature. This contrasts with nonintegrated economizers where switching from economizer
to chillers can be disruptive and guessing wrong about

www.info.hotims.com/49805-22
J u n e 2014

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ASHRAE JouRnAl

35



ASHRAE Journal - June 2014

Table of Contents for the Digital Edition of ASHRAE Journal - June 2014

Contents
ASHRAE Journal - June 2014 - Cover1
ASHRAE Journal - June 2014 - Cover2
ASHRAE Journal - June 2014 - 1
ASHRAE Journal - June 2014 - 2
ASHRAE Journal - June 2014 - Contents
ASHRAE Journal - June 2014 - 4
ASHRAE Journal - June 2014 - 5
ASHRAE Journal - June 2014 - 6
ASHRAE Journal - June 2014 - 7
ASHRAE Journal - June 2014 - 8
ASHRAE Journal - June 2014 - 9
ASHRAE Journal - June 2014 - 10
ASHRAE Journal - June 2014 - 11
ASHRAE Journal - June 2014 - 12
ASHRAE Journal - June 2014 - 13
ASHRAE Journal - June 2014 - 14
ASHRAE Journal - June 2014 - 15
ASHRAE Journal - June 2014 - 16
ASHRAE Journal - June 2014 - 17
ASHRAE Journal - June 2014 - 18
ASHRAE Journal - June 2014 - 19
ASHRAE Journal - June 2014 - 20
ASHRAE Journal - June 2014 - 21
ASHRAE Journal - June 2014 - 22
ASHRAE Journal - June 2014 - 23
ASHRAE Journal - June 2014 - 24
ASHRAE Journal - June 2014 - 25
ASHRAE Journal - June 2014 - 26
ASHRAE Journal - June 2014 - 27
ASHRAE Journal - June 2014 - 28
ASHRAE Journal - June 2014 - 29
ASHRAE Journal - June 2014 - 30
ASHRAE Journal - June 2014 - 31
ASHRAE Journal - June 2014 - 32
ASHRAE Journal - June 2014 - 33
ASHRAE Journal - June 2014 - 34
ASHRAE Journal - June 2014 - 35
ASHRAE Journal - June 2014 - 36
ASHRAE Journal - June 2014 - 37
ASHRAE Journal - June 2014 - 38
ASHRAE Journal - June 2014 - 39
ASHRAE Journal - June 2014 - 40
ASHRAE Journal - June 2014 - 41
ASHRAE Journal - June 2014 - 42
ASHRAE Journal - June 2014 - 43
ASHRAE Journal - June 2014 - 44
ASHRAE Journal - June 2014 - 45
ASHRAE Journal - June 2014 - 46
ASHRAE Journal - June 2014 - 47
ASHRAE Journal - June 2014 - 48
ASHRAE Journal - June 2014 - 49
ASHRAE Journal - June 2014 - 50
ASHRAE Journal - June 2014 - 51
ASHRAE Journal - June 2014 - 52
ASHRAE Journal - June 2014 - 53
ASHRAE Journal - June 2014 - 54
ASHRAE Journal - June 2014 - 55
ASHRAE Journal - June 2014 - 56
ASHRAE Journal - June 2014 - 57
ASHRAE Journal - June 2014 - 58
ASHRAE Journal - June 2014 - 59
ASHRAE Journal - June 2014 - 60
ASHRAE Journal - June 2014 - 61
ASHRAE Journal - June 2014 - 62
ASHRAE Journal - June 2014 - 63
ASHRAE Journal - June 2014 - 64
ASHRAE Journal - June 2014 - 65
ASHRAE Journal - June 2014 - 66
ASHRAE Journal - June 2014 - 67
ASHRAE Journal - June 2014 - 68
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ASHRAE Journal - June 2014 - 70
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ASHRAE Journal - June 2014 - 73
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ASHRAE Journal - June 2014 - 79
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ASHRAE Journal - June 2014 - 81
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ASHRAE Journal - June 2014 - 84
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ASHRAE Journal - June 2014 - 86
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ASHRAE Journal - June 2014 - Cover3
ASHRAE Journal - June 2014 - Cover4
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