Page 349 - HVAC Pump Handbook

Rishel_CH11.qxd 20/4/06 6:37 PM Page 346

Open Cooling Tower Pumps

346 Pumps for Open HVAC Cooling Systems

3
gas at 1000 Btu/ft , this is equivalent to 37,500 mcf of natural gas, or
$112,500 per year.
Unfortunately, the average return water temperature to cooling tow-
ers is only 95°F. As HVAC water processes reduce their temperature,
more of this heat will become economically retrievable. Programs are
now being evaluated for raising the condenser leaving water tempera-
ture and balancing the cost of eliminating boiler operation against the
higher kilowatt per ton cost incurred by running the chillers at higher
leaving condenser temperatures.
This is an excellent place to again evaluate kilowatt per ton instru-
mentations and calculations for heat recovery systems. By measuring
the kilowatt consumption of the chillers, pumps, and cooling towers,
as well as the tonnage on the chilled water system, the data are
achieved for measuring kilowatts per ton for the heat recovery sys-
tem. Also, by determining the heat recovered from closed condenser
heat recovery circuits, a total energy statement can be derived that
will provide a guide for the central plant operator to program the
equipment at the maximum possible efficiency. There is no way an
operator can read all these system values simultaneously and develop
a manual algorithm that will give the continuous and accurate data
that are achievable with these computer programs.
The great amount of heat rejected by cooling towers should be
remembered as we go about the business of making chilled and hot
water systems more efficient. Some of the current efforts will be found
in Chap. 16 on closed condenser systems. Also, systems are prime can-
didates for evaluation for heat recovery from cooling towers if they
have chillers and boilers that operate at the same time. Chiller opera-
tion in the winter and boiler operation in the summer may be signals
to evaluate the economics of heat recovery.

11.9 Bibliography
James B. Rishel, The Water Management Manual, SYSTECON, Inc., West Chester,
Ohio, 1992.
Cooling Tower Fundamentals, The Marley Cooling Tower Company, Mission, Kan.,
1985.

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2006 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.