5.12 Pumping
systems (less than 4.4C) (less than 40F). The
concentration of antifreeze shall be kept to a practical
and Piping Systems
minimum because of its adverse effect on heat exchange
efficiency and pump life. The water make-up line for
glycol systems shall be provided with an in-line water
All HVAC piping systems shall be designed and sized in
meter to monitor and maintain the proper percentage of
accordance with ASHRAE Fundamentals Handbook and
glycol in the system. All coils exposed to outdoor airflow
the ASHRAE HVAC Systems and Equipment Handbook.
(at some time) shall be provided with freeze protection
Materials acceptable for piping systems are black steel
thermostats and control cycles. Provisions shall be made
and copper. No PVC or other types of plastic pipe are
for drain down, storage and re-injection of the glycol into
permitted.
the system.
The hot water and chilled water systems shall utilize a
Waterside Economizer Cycle. In certain climate
two-pipe main distribution system arranged in a reverse
conditions cooling towers are capable of producing
return configuration. Loop piping for terminal or branch
condenser water cold enough to cool the chilled water
circuits shall be equipped with automatic flow control
system without chiller operation. This option shall be
valves. Each terminal unit or coil shall be provided with
considered in life cycle cost analysis of water cooled
isolation valves on both the supply and return, and a
chillers. Waterside economizer cycles are particularly cost
flow-indicating balance valve on the return line. Isolation
effective in the low humidity climates of the western
valves shall be provided on all major pipe branches, such
United States. Waterside economizer systems shall be used
as at each floor level, building wing or mechanical room.
only in areas where the outdoor air temperature shall be
below 4.4C (40F) wet bulb. Waterside economizers shall
Hydronic, Closed Loop Systems. Pumps used in closed
utilize a plate heat exchanger piped in parallel
loop hydronic piping shall be designed to operate to the
arrangement with its respective chiller.
left of the peak efficiency point on their curves (higher
head, less flow), to compensate for variances in pressure
drop between calculated and actual values without
causing pump overloading. Pumps with steep curves shall
not be used, as they tend to limit system flow rates. Flow
may be varied by variable speed pumps or staged multiple
pumps. Pumps shall operate at no less than 75%
efficiency on their performance curve.
Variable Primary Pumping. In this application, the
primary circuit serves source equipment (chiller or boiler)
and the load. The primary loop and pumps are dedicated
and sized to serve the flow and temperature differential
requirements of the primary source equipment and the
load. Variable primary systems are only recommended for
147
MECHANICAL
ENGINEERING
5.12
Pumping and Piping Systems
Revised March 2005 PBS-P100
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