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38 Chiller System Design and Control SYS-APM001-EN
System Design Options
In both cases, either reusing an existing tower, or reusing existing chilled
water piping, the design engineer can often help reduce total project costs
using the existing infrastructure by selecting a chiller with a higher
temperature differential.
Cost Implications
By reducing either chilled- or condenser-water flow rates, the following
installed-cost reductions are possible:
• Reduced size of pumps, valves, strainers, fittings, and electrical
connections
• In new systems, reduced pipe sizes
• In existing systems, more capacity from existing chilled-water piping
• Reduced cooling-tower size, footprint, and fan power
If a physically-smaller cooling tower is selected using low flow, its reduced
footprint can benefit building owners in a number of ways:
• Reduced real estate requirements (often more important than realized)
• Reduced structural requirement, since the amount of tower water is
reduced
• Reduced excavation and material costs in the case of a large, built-up
tower with a concrete sump
• Improved aesthetics because of the reduced tower height
In addition to reducing installation costs, operating cost reductions for the
whole system are also available. Due to a smaller pump and/or tower, the
pump and tower operating costs can be reduced substantially with less
adverse impact on the chiller operating cost. Analysis programs such as
EnergyPlus, eQuest, TRACE™, or System Analyzer™ software can be used to
determine annual operating costs. Nordeen and Schwedler
11
showed that
operating costs for chilled-water systems using absorption chillers can
benefit greatly from reduced condenser-water flow. Figure 23 shows
operating costs as generated with System Analyzer analysis software.
Several considerations should be kept in
mind when determining sizes for new
systems. As pipe size is decreased, so
are valve and specialty sizes and costs.
Remember that reducing pipe size
increases pressure drop. Keep a balance
between first cost and operating costs.
This can significantly reduce the system
retrofit costs because existing pipes may
be used
.