ASHRAE Journal - April 2020 - 68

ENGINEERS NOTEBOOK
COLUMN

Nathan Ho

Optimizing Campus
Chilled Water
Connections
BY NATHAN HO, P.E., ASSOCIATE MEMBER ASHRAE

Campuses and institutions often use centralized plants with chilled water distribution infrastructure to provide cooling to multiple buildings for the various operational and packaging benefits that come with a central utility plant scheme. The way
these buildings connect to the chilled water distribution infrastructure can have a
significant impact on the performance of the central plant and on the HVAC systems
in the building. Although several articles have been written about this topic over the
years,1 - 4 the author has recently observed examples where campus chilled water
design fundamentals have been misapplied, so our design community may benefit
from a refresher.
Optimizing Pumping Energy Performance
Chilled water distribution pumps located at the central plant are often the largest consumers of pump
energy on a campus due to the entire campus chilled
water flow moving through them. Inspecting the pump
head equation in Figure 1 reveals that an effective way to
reduce their power draw and overall energy consumption is to lower their operating pressure requirements.
This is where design of campus chilled water building
connections comes in.
The most efficient campus pumping scheme involves
operating the central plant chilled water distribution pumps with just enough pressure to overcome
the friction and fitting losses required to pump water
through the distribution piping with a small margin
68

ASHRAE JOURNAL

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APRI L 2020

of additional pressure to achieve a slight positive
pressure delta at the most remote building connections. This approach is described by this author as the
"lazy river" strategy and relies on booster pumps to be
provided at buildings that require more head pressure than the coincident campus distribution pressure available at their connection. Figure 2 shows an
example of a boosted-secondary pumping building
connection. These building booster pumps are effectively operating in series with the central plant chilled
water distribution pumps and are controlled to meet
the pump head pressure requirements specific to their
local HVAC loads.
Nathan Ho, P.E., is an associate principal and engineering group leader with P2S Inc., in Irvine,
Calif. He is the chair of ASHRAE SPC 110, vice chair of TC 4.3, and member of TC 9.10.


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ASHRAE Journal - April 2020

Table of Contents for the Digital Edition of ASHRAE Journal - April 2020

Contents
ASHRAE Journal - April 2020 - Intro
ASHRAE Journal - April 2020 - Cover1
ASHRAE Journal - April 2020 - Cover2
ASHRAE Journal - April 2020 - 1
ASHRAE Journal - April 2020 - Contents
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ASHRAE Journal - April 2020 - Cover3
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