Page 207 - HVAC Pump Handbook

Rishel_07.qxd 20/4/06 6:29 PM Page 204

Pump Drivers and Variable-Speed Drives

204 HVAC Pumps and Their Performance

Total pump control is so dependent on the water system character-
istics that it is often included with its software in a pumping sys-
tem control center (see Fig. 7.16b).
Contemporary software is so flexible that the pump-control cen-
ter can be interfaced with the rest of the building management
system through data-gathering panels or protocols such as
BACnet that is being developed by ASHRAE. Practically, there is
seldom any need for any special software or interfacing at the
point of installation.

Variable-frequency drives have become so standard for the HVAC
pumping industry that there is no reason why there should not be a
reliable variable-frequency drive with a minimum of service for any
HVAC variable-speed pumping system.

7.4 Steam Turbine Drives for HVAC Pumps
On a central energy plant with high-pressure boilers, there may be
high-pressure steam available for operating HVAC pumps. These
turbine-operated pumps could be for boiler feed service as well as
chilled and hot water system pumps. Steam turbine drives on pumps
may be economical where large chillers are driven by steam turbines.
The overall heat cycle for the boiler plant may indicate economies if
the pumps are turbine-driven as well, taking exhaust steam from the
chiller turbines. This is a detailed economic evaluation that must be
made by the boiler room designer.
On installations where high-pressure steam is available but the
chillers or other major boiler house equipment are not turbine-driven,
it may be economical to equip certain pumps with turbines for use
during periods that have high electrical demand charges. Typical of
this are systems using storage chilled water to reduce the peak power
during these periods of high demand charges.
Steam turbines usually operate with horizontal double-suction
pumps. Steam turbine selection is based on the maximum brake
horsepower required by the pump. Other parameters that must be
determined are minimum supply steam pressure and maximum
exhaust pressure.
Turbines are rated in brake horsepower capability at a certain
water rate. Water rate is the pounds of steam per hour consumed
when the turbine is operating at a particular speed and brake horse-
power.
Turbine speed control consists of a supply steam pressure regulator
that receives an analog signal from the pumping system controller.
Turbine speed control is much like that for variable-frequency drives.

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.