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Source: HVAC Pump Handbook

Part

The Basic Tools

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The Basic Tools

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)

Any use is subject to the Terms of Use as given at the website.

Source: HVAC Pump Handbook

Digital Electronics

and HVAC Pumps

Chapter

1.1 Introduction

The emergence of digital electronics has had a tremendous impact on in-

dustrial societies throughout the world. In the heating, ventilating, and

air-conditioning (HVAC) industry, the development of digital electronics

has brought an end to the use of many mechanical devices; typical of

this is the diminished use of mechanical controls for HVAC air and

water systems. Today’s digital control systems, with built-in intelligence,

more accurately evaluate water and system conditions and adjust pump

operation to meet the desired water flow and pressure conditions.

Drafting boards and drafting machines have all but disappeared from

the design rooms of heating, ventilating, and air-conditioning engineers

and have been replaced by computer-aided drafting (CAD) systems.

Tedious manual calculations are being done more quickly and accurately

by computer programs developed for specific design applications. All

this has left more time for creative engineering on the part of designers

to the benefit of the client.

1.2 Computer-Aided Calculation of HVAC

Loads and Pipe Friction

The entire design process for today’s water systems, from initial design

to final commissioning, has been simplified and improved as a result of

the new, sophisticated computer programs. One of the most capable

programs for sizing and analyzing flow in fluid systems is the piping

systems analysis program developed by APEC, Inc. (Automated

Procedures for Engineering Consultants), headquartered in Dayton,

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Digital Electronics and HVAC Pumps

The Basic Tools

Ohio. APEC, a nonprofit, worldwide association of consulting engineers

and in-house design group, is dedicated to improving quality and pro-

ductivity in the design of HVAC air and water systems through the de-

velopment and application of advanced computer software.

The APEC PSA-1 program accurately calculates the friction losses

and sizes of pipes as well as simulating flow under different operating

conditions in either new or existing piping systems. Analyzing the

fluid flow in systems with diversified loads, multiple pumps, and

chillers or boilers is essential if engineers are to truly understand the

real operating conditions of large HVAC water systems. This under-

standing can only be achieved through the use of a computer program

capable of such thorough analysis.

1.2.1 Typical input for APEC piping system

analysis program

The following is representative system data into an APEC’s computer

program for calculating pipe sizing, friction, and flow analysis, and

typical output.

Master Data files

Pipe, fitting, and valve files

Material

friction loss

Actual ID for nominal

copper type (M,L)

Steel schedule

other

Standard pipe pre-entered or custom. Cost estimation optional.

Insulation file

Type

K value

Thickness

Cost estimation optional

Fluids . Provisions for all fluid types with:

Density

Temperature

Viscosity

Specific heat

System data

Pipe environment Required for heat/loss gain

Space temperature

Outside air temperature

Soil conductivity

Burial depth

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Digital Electronics and HVAC Pumps

Program options

System sizing

Flow simulation

Cost estimate

Flow simulation options - typical entries

Maximum iterations

Intermediate results

Every 3 iterations

Temperature tolerance for convergence

0.50

Relaxation parameters

0.50°F

Fill pressure

46 ft of head (or H 2 O)

Pump data

Variable or constant speed

Points for pump curves

Terminal data (coils, etc.)

Fluid flow

Pressure drop

Coil cfm (ft 3 /min)

Inlet air temperature

Leaving air set point

Valve data

Valve coefficient

Trial setting

Valve control

1.2.2 Typical output for APEC piping

system analysis program

Table 1.1 includes samples of output headings, with one line of output

for only three output forms available. The output also has forms that

mirror the input, so the designer has a complete record of the entire

analysis.

This program is now being expanded to include many additional

piping features and to accommodate contemporary computer prac-

tices such as Windows, to speed the development and manipulation of

project data.

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)

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J. B. Rishel - HVAC Pump Handbook.pdf

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