Page 13 - HVAC Pump Handbook

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Digital Electronics and HVAC Pumps

10 The Basic Tools

1.8 Electronic Selection of HVAC Equipment

A major part of the designer’s work is the selection of equipment for a
water system. This includes, for example, chillers, cooling towers, boil-
ers, pumping systems, heating and cooling coils, and control systems.
In the past, designers depended on manufacturers’ catalogs to furnish
the technical information that provided the selection of the correct
equipment for a water system. This had to do with the hope that the
catalogs were current. Now comes the CD-ROM disc and on-line data
services that provide current information and rapid selection of
equipment that meets the designer’s specifications. Many manufac-
turers are converting their technical catalogs to software such as CD-
ROM discs, providing both performance and dimensional data. The
day of the technical catalog is almost gone.

1.9 Electronic Control of HVAC Water Systems

Along with these changes in mechanical design, electronic control of
HVAC water systems, in the form of direct digital control or program-
mable-logic controllers, has all but eliminated older mechanical control
systems such as pneumatic control. The advent of universal protocols
®
such as BACnet has enabled most control and equipment manufactur-
ers to interface together on a single installation. BACnet description is
available from ASHRAE headquarters in Atlanta, Georgia.

1.10 Electronics and HVAC Pumps
How do all these electronic procedures relate to HVAC pumps?
Efficient pump selection and operation depend on the accurate calcu-
lation of a water system’s flow and pump head requirements. Digital
electronics has created greater design accuracy, which guarantees bet-
ter pump selection. Incorrect system design will result in (1) pumps
that are too small and incapable of operating the water system or (2)
pumps that are too large with excess flow and head resulting in ineffi-
cient operation. The use of electronic design aids has improved the
chances of selecting an efficient pumping system for each application.
Accurate calculation of flow and head requirements of constant-vol-
ume HVAC systems has reduced the energy destroyed in balance
valves that are used to eliminate excessive pressure.

1.11 Electronics and Variable-Speed Pumps
One of the greatest effects on HVAC water systems of electronics is
the development of variable-frequency drives for fans and pumps. The
day of the constant-speed pump with its fixed head-capacity curve is

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