Retrotec USACE - Manual (Page 199)

Appendix D D69
average use 8.706 L (2.3 gal) for every kWh of electrical energy produced. So,
every kWh of electrical savings, regardless of what it is used for, saves approxi-
mately 8.706 L (2.3 gal) of water.
D.4.2.11 Cooling Plants Are Primary/Secondary Systems and Are
Equipped with Constant-Speed Primary Chilled Water Pumps
(Ineffi ciency)
Figure D121. Central cooling plant primary
chilled water pump.
Typical cooling plants are primary/secondary systems and are equipped with
constant-speed primary chilled water pumps (Figure D121). These constant-
speed pumps pull the same amount of power when the chiller is at 100% load
as they do when the chiller is at 10% load. At full chiller load, these pumps con-
tribute approximately 0.03 kW per ton, while at 10% chiller load, these pumps
contribute 0.3 kW per ton—a 1,000% increase in the energy consumption pen-
alty for this auxiliary equipment when the system is running at light loads.
The design of the primary chilled water pumping system should be modi-
fi ed to provide chilled water fl ow rates through the chillers that are propor-
tional to the chiller load and system temperature differential. Doing so will
reduce annual primary chilled water pumping system energy waste in excess
of 50% for many installations.
Changing the design strategy from a primary/secondary system confi gu-
ration to a primary-only, variable fl ow (POVF) system confi guration using
variable fl ow chilled water pumps reduces fi rst costs and operating costs. As
an added benefi t, installation of variable-speed drives on the primary chilled
water pumps will allow many of the primary pumps to be oversped up to the
current limit on the pump motors to increase the fl ow rate through the chillers
when the system temperature differential is low, to reduce the energy waste
associated with the “Low Delta T Syndrome.” This higher primary loop fl ow
rate will allow the chiller that is running during a low temperature differential
situation to be more fully loaded prior to starting another chiller, as would typi-
cally be done to ensure that the primary loop fl ow exceeds the secondary loop
fl ow rate.
A higher primary loop fl ow rate, when needed, can reduce chiller and con-
denser water pump energy waste that would be incurred when a chiller that is
not needed is started, so that its primary loop pump can increase the primary