ASHRAE Journal - October 2013 - 48

Column EnginEEr’s notEbook
Steven T. Taylor

Tips to Reduce Chilled
Water Plant Costs
By Steven t. taylor, P.e., Fellow aSHrae

A chilled water plant can be conceptually well designed but implemented in
a manner that unnecessarily increases first costs, sometimes substantially.
Here are a few tips to reduce the first costs of a chilled water plant without
reducing performance.
Tip 1: Piping and Pumps
Figure 1 shows a chilled water plant with primary-only
pumping. Conceptually the design is fine, and in fact
the primary-only design is a good step in reducing plant
costs since it is less expensive than primary-secondary
pumping.1 But the designer of this plant unnecessarily
increased first costs.
First, “reverse return” piping was provided for both
condenser water and chilled water systems. Reverse
return, where the first device supplied is the last
returned, is a piping scheme intended to self-balance
hydronic systems, but more importantly, to keep the
pressure drop across modulating two-way control valves
relatively low and equal among all valves as they open
and close with changing loads. It can be an effective
technique to improving controllability of large (high
pressure drop) variable flow hydronic distribution
systems.2
But in this case, the valves at each chiller are essentially two-position and the difference in pressure across
each valve is very small even if the system is directreturn (first supplied, first returned) and was not manually balanced. A balanced direct-return piping system
will result in the same flow rates across each chiller as
the reverse-return design regardless how many chillers
were enabled. So there is absolutely no value in performance to reverse-return in this application, yet it substantially increases first costs.
Another often expensive design concept is to gang
pumps together and pipe all the pumps first to a larger
common pipe before distributing the supply water to
the chillers. In this example, the common pipe size
48

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is 12 in. (nominal 300 mm) on the chilled water side
and 14 in. (nominal 350 mm) on the condenser water
side. It is not uncommon to see all the pumps squished
into a corner of the chiller room. There is little synergy
to ganging pumps next to each other yet doing so can
increase first costs and reduce space around the pumps
for maintenance.
Figure 2 shows the same plant as Figure 1 but instead
of reverse-return and ganged pumps, the pumps are
aligned with chillers and are piped into a common
header on the discharge side of the pump and also on
the discharge side of the condensers. (The discharge side
of the evaporators is the same as that in Figure 1.) This
design still allows any pump to serve any chiller, but it
shortens piping runs and it reduces pipe sizes because
there is no common pipe that sees the total system flow.
On the condenser water side, all pipes are 10 in.
(nominal 250 mm)—the 14 in. (nominal 350 mm) common pipe is eliminated. Similarly, the 12 in. (nominal
300 mm) chilled water piping at the discharge of the
pump to the evaporators is eliminated; all pipes are 8 in.
(nominal 200 mm). First costs are substantially reduced
with no impact on performance.
This layout also usually reduces the footprint of
the plant, reducing the floor area required for the
chiller room. In fact, locating the equipment as
close together as possible is key to the first cost savings. Figure 3 shows a floor plan of the plant shown
schematically in Figure 2. The chilled and condenser
Steven T. Taylor, P.E., is a principal of Taylor Engineering in Alameda, Calif. He is a member of SSPC 90.1 and chair of TC 4.3, Ventilation Requirements and Infiltration.



ASHRAE Journal - October 2013

Table of Contents for the Digital Edition of ASHRAE Journal - October 2013

Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Sustainable Design of Water Source VRF
Economizer for Data Center
Total Dissolved Solids in Reclaimed Water
Hot, Humid Lab Hood Facility
Engineer's Notebook
Building Sciences
The Performance Gap
ASHRAE Honor Roll
ASHRAE Research Report
Technical vs. Process Commissioning: Basis of Design
Emerging Technologies
Data Centers
HVAC Applications
Energy Modeling
Refrigeration Applications
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - October 2013 - Cover1
ASHRAE Journal - October 2013 - Cover2
ASHRAE Journal - October 2013 - 1
ASHRAE Journal - October 2013 - 2
ASHRAE Journal - October 2013 - Contents
ASHRAE Journal - October 2013 - Commentary
ASHRAE Journal - October 2013 - 5
ASHRAE Journal - October 2013 - Industry News
ASHRAE Journal - October 2013 - 7
ASHRAE Journal - October 2013 - 8
ASHRAE Journal - October 2013 - 9
ASHRAE Journal - October 2013 - Letters
ASHRAE Journal - October 2013 - 11
ASHRAE Journal - October 2013 - Meetings and Shows
ASHRAE Journal - October 2013 - 13
ASHRAE Journal - October 2013 - Sustainable Design of Water Source VRF
ASHRAE Journal - October 2013 - 15
ASHRAE Journal - October 2013 - 16
ASHRAE Journal - October 2013 - 17
ASHRAE Journal - October 2013 - 18
ASHRAE Journal - October 2013 - 19
ASHRAE Journal - October 2013 - Economizer for Data Center
ASHRAE Journal - October 2013 - 21
ASHRAE Journal - October 2013 - 22
ASHRAE Journal - October 2013 - 23
ASHRAE Journal - October 2013 - 24
ASHRAE Journal - October 2013 - 25
ASHRAE Journal - October 2013 - 26
ASHRAE Journal - October 2013 - 27
ASHRAE Journal - October 2013 - Total Dissolved Solids in Reclaimed Water
ASHRAE Journal - October 2013 - 29
ASHRAE Journal - October 2013 - 30
ASHRAE Journal - October 2013 - 31
ASHRAE Journal - October 2013 - 32
ASHRAE Journal - October 2013 - 33
ASHRAE Journal - October 2013 - 34
ASHRAE Journal - October 2013 - 35
ASHRAE Journal - October 2013 - 36
ASHRAE Journal - October 2013 - 37
ASHRAE Journal - October 2013 - 38
ASHRAE Journal - October 2013 - 39
ASHRAE Journal - October 2013 - Hot, Humid Lab Hood Facility
ASHRAE Journal - October 2013 - 41
ASHRAE Journal - October 2013 - 42
ASHRAE Journal - October 2013 - 43
ASHRAE Journal - October 2013 - 44
ASHRAE Journal - October 2013 - 45
ASHRAE Journal - October 2013 - 46
ASHRAE Journal - October 2013 - 47
ASHRAE Journal - October 2013 - Engineer's Notebook
ASHRAE Journal - October 2013 - 49
ASHRAE Journal - October 2013 - 50
ASHRAE Journal - October 2013 - 51
ASHRAE Journal - October 2013 - 52
ASHRAE Journal - October 2013 - 53
ASHRAE Journal - October 2013 - Building Sciences
ASHRAE Journal - October 2013 - 55
ASHRAE Journal - October 2013 - 56
ASHRAE Journal - October 2013 - 57
ASHRAE Journal - October 2013 - 58
ASHRAE Journal - October 2013 - 59
ASHRAE Journal - October 2013 - The Performance Gap
ASHRAE Journal - October 2013 - 61
ASHRAE Journal - October 2013 - 62
ASHRAE Journal - October 2013 - 63
ASHRAE Journal - October 2013 - 64
ASHRAE Journal - October 2013 - ASHRAE Honor Roll
ASHRAE Journal - October 2013 - HR 2
ASHRAE Journal - October 2013 - HR 3
ASHRAE Journal - October 2013 - HR 4
ASHRAE Journal - October 2013 - HR 5
ASHRAE Journal - October 2013 - HR 6
ASHRAE Journal - October 2013 - HR 7
ASHRAE Journal - October 2013 - HR 8
ASHRAE Journal - October 2013 - HR 9
ASHRAE Journal - October 2013 - HR 10
ASHRAE Journal - October 2013 - HR 11
ASHRAE Journal - October 2013 - HR 12
ASHRAE Journal - October 2013 - HR 13
ASHRAE Journal - October 2013 - HR 14
ASHRAE Journal - October 2013 - HR 15
ASHRAE Journal - October 2013 - HR 16
ASHRAE Journal - October 2013 - HR 17
ASHRAE Journal - October 2013 - HR 18
ASHRAE Journal - October 2013 - HR 19
ASHRAE Journal - October 2013 - HR 20
ASHRAE Journal - October 2013 - HR 21
ASHRAE Journal - October 2013 - HR 22
ASHRAE Journal - October 2013 - HR 23
ASHRAE Journal - October 2013 - HR 24
ASHRAE Journal - October 2013 - HR 25
ASHRAE Journal - October 2013 - HR 26
ASHRAE Journal - October 2013 - HR 27
ASHRAE Journal - October 2013 - HR 28
ASHRAE Journal - October 2013 - HR 29
ASHRAE Journal - October 2013 - HR 30
ASHRAE Journal - October 2013 - HR 31
ASHRAE Journal - October 2013 - HR 32
ASHRAE Journal - October 2013 - ASHRAE Research Report
ASHRAE Journal - October 2013 - 66
ASHRAE Journal - October 2013 - 67
ASHRAE Journal - October 2013 - 68
ASHRAE Journal - October 2013 - 69
ASHRAE Journal - October 2013 - 70
ASHRAE Journal - October 2013 - 71
ASHRAE Journal - October 2013 - 72
ASHRAE Journal - October 2013 - 73
ASHRAE Journal - October 2013 - 74
ASHRAE Journal - October 2013 - 75
ASHRAE Journal - October 2013 - Technical vs. Process Commissioning: Basis of Design
ASHRAE Journal - October 2013 - 77
ASHRAE Journal - October 2013 - 78
ASHRAE Journal - October 2013 - 79
ASHRAE Journal - October 2013 - 80
ASHRAE Journal - October 2013 - 81
ASHRAE Journal - October 2013 - Emerging Technologies
ASHRAE Journal - October 2013 - 83
ASHRAE Journal - October 2013 - 84
ASHRAE Journal - October 2013 - 85
ASHRAE Journal - October 2013 - 86
ASHRAE Journal - October 2013 - 87
ASHRAE Journal - October 2013 - Data Centers
ASHRAE Journal - October 2013 - 89
ASHRAE Journal - October 2013 - 90
ASHRAE Journal - October 2013 - 91
ASHRAE Journal - October 2013 - 92
ASHRAE Journal - October 2013 - 93
ASHRAE Journal - October 2013 - HVAC Applications
ASHRAE Journal - October 2013 - 95
ASHRAE Journal - October 2013 - Energy Modeling
ASHRAE Journal - October 2013 - 97
ASHRAE Journal - October 2013 - Refrigeration Applications
ASHRAE Journal - October 2013 - 99
ASHRAE Journal - October 2013 - Products
ASHRAE Journal - October 2013 - 101
ASHRAE Journal - October 2013 - 102
ASHRAE Journal - October 2013 - Classified Advertising
ASHRAE Journal - October 2013 - Advertisers Index
ASHRAE Journal - October 2013 - Cover3
ASHRAE Journal - October 2013 - Cover4
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