Handbook of air conditioning and refrigeration / Shan K

7.58 CHAPTER SEVEN
DDC system controller is used for each type of building. There is a central microprocessor for the
whole chilled water system. The optimization program may proceed as follows:
1. Measure the chilled water temperature across each load and source, as well as its rate of water
flow.
2. Add all the loads.
3. Turn on the most efficient source first, including the demand and downtime, according to available
sources. A chiller’s running capacity should match the required loads. There should be a
time delay to start or stop the chiller.
4. Use trending and expert system control strategies to predict load changes according to past experience
and outdoor conditions.
Chilled and Hot Water Distribution Pipes
Chilled and hot water distribution pipes are large pipes mounted in underground accessible tunnels
or trenches. They are well insulated, although underground return chilled water mains for which return
temperature T ret � 60°F (15.6°C) may not be insulated, depending on a detailed cost analysis.
Factory-made conduits consist of inner steel pipe, insulation, airspace, and outer conduit; or steel
pipe, with and without insulation, and outer casing. Expansion loops or couplings should be included,
and a good drainage system is important to protect the insulating quality. Please refer to
ASHRAE Handbook 1996, HVAC Systems and Equipment, chapter 11, for details on design and installation.
7.14 COMPUTER-AIDED PIPING DESIGN AND DRAFTING
General Information
According to “Selecting Piping System Software” by Amistadi (1994), three currently widely used
piping design and drafting computer programs were reviewed: University of Kentucky’s
KYCAD/KYPIPE, Trane’s Water Piping Design, and Softdesk’s Piping. The Trane and Softdesk
computer programs require AutoCAD as a base product whereas the University of Kentucky software
has its own integrated CAD system.
The University of Kentucky programs have extensive hydraulic modeling capacities including
transient analysis. They are intended for mechanical engineers and are used to design and analyze
large, complex water systems. Trane’s and Softdesk’s software programs are limited to steady-state
imcompressible fluids. They are intended for contractors, mechanical engineers, and drafters. Kentucky’s
and Softdesk’s programs support both inch-pound and metric units, while Trane’s package
supports only inch-pound units. The University of Kentucky software requires 2.0 Mbytes of disk
space and 2.0 Mbytes RAM. Softdesk’s software requires 10 Mbytes disk space and 8 Mbytes
RAM. Trane’s software requires the most disk space—10 Mbytes and 12 Mbytes RAM. The
University of Kentucky program is MS-DOS applications, whereas Trane’s and Softdesk’s are
available for Windows platforms.
Computer-Aided Drafting Capabilities
Trane’s piping software allows designers to create a schematic two-dimensional (2D) piping system
in AutoCAD and to link to the computer programs of piping size calculations for use in piping system
design. Softdesk’s software is intended for drafting in 2D or 3D graphics. Design information
databases and engineering analysis software programs are linked to the drawing for support. The