Handbook of air conditioning and refrigeration / Shan K

Many companies are assembling quality assurance programs which show that they are accepting
compliance to ISO 9000 standards instead of registration. Such an arrangement will identify the
ISO 9000 standard that can be best applied to your operation and also support your customer’s ISO
9000 quality audit.
1.12 COMPUTER-AIDED DESIGN AND DRAFTING (CADD)
Features of CADD
Computer-Aided Design
INTRODUCTION 1.25
Because personal computers (PCs) provide a low-cost tool for computations and graphics and
owing to the availability of lots of design computer software during the 1980s, computer-aided
design and drafting (CADD) for air conditioning systems has grown quickly in recent years. Today,
computer software is often used to develop design documents, drawings, and specifications in common
use in engineering consulting firms. According to the 1994 CADD Application and User
Survey of design firms in Engineering Systems (June 1994), “ ...firms with high productivity
reported that they perform 95 percent of projects on CADD.”
In addition to the CADD, there is software available for computer-aided facilities management
(CAFM) for operation and maintenance.
Compared with conventional design and drafting, CADD of air conditioning systems has the following
features:
● Different trade designers such as those in architecture, HVAC&R, plumbing, fire protection, and
electrical engineers can merge their work in plot output files to produce composite drawings in
different layers. Mechanical system design can integrate with equipment selection programs.
● Graphical model construction of air conditioning systems and subsystems in two-dimensional
(2D) or three-dimensional (3D) presentation uses architectural and structural models as backgrounds.
● CADD links the engineering design models based on calculation and the graphical model based
on drafting.
● It provides the ability to develop and compare the alternate design schemes quickly as well as the
capability to redesign or to match the changes during construction promptly.
● CADD establishes database libraries for design and graphical models.
● It develops design documents including as-built drawings and equipment schedules.
A saving of design time up to 40 percent has been claimed by some engineering consulting firms.
Current CADD for HVAC&R systems can be classified into two categories: (1) engineering design
and simulation, and (2) drafting graphical model construction. The software for engineering design
can again be subdivided into the following groups:
● Load calculations, energy simulation, and psychrometric analysis. Software for space load calculations
could be a part of the energy simulation software. However, load calculations are often
mainly used to determine the peak or block load at design conditions. These loads are the inputs
for equipment selection. However, the software for energy simulation is used mainly to determine
the optimum selection from different alternatives. Psychrometric analysis is sometimes a useful
tool for load calculation and energy simulation.