Ashrae 2000 HVAC Systems and Equipment Handbook.pdf

ASHRAE Research: Improving the Quality of Life

The American Society of Heating, Refrigerating and Air-Condi-

tioning Engineers is the world’s foremost technical society in the

fields of heating, ventilation, air conditioning, and refrigeration. Its

members worldwide are individuals who share ideas, identify the

need for and support research, and write the industry’s standards for

testing and practice. The result of these efforts is that engineers are

better able to keep indoor environments safe and productive while

protecting and preserving the outdoors for generations to come.

One of the ways that ASHRAE supports its members’ and indus-

try’s need for information is through ASHRAE Research. Thou-

sands of individuals and companies support ASHRAE Research

The 2000 ASHRAE Handbook

The 2000 ASHRAE Handbook—HVAC Systems and Equipment

describes both the combinations of equipment and the components

or assemblies that perform a particular function either individually

or in combination. The information helps the system designer select

and operate equipment, although it does not describe how to design

components.

Major topic areas include

• Air-conditioning and heating systems

• Air-handling equipment

• Heating equipment

• General HVAC components

• Unitary equipment

Most of the chapters in this Handbook update material in the

1996 ASHRAE Handbook to reflect current technology. The follow-

ing chapters contain major revisions or new material.

• Chapters 1 through 5 are reorganized and tightened for clarity.

Chapter 2, Building Air Distribution, contains expanded cover-

age on VAV systems, including more information on terminal

units. Chapter 4, Central Cooling and Heating, is a new chapter

that introduces central plant equipment and options.

• Chapter 7, Cogeneration Systems and Engine and Turbine Drives,

has more information on combustion turbine inlet air cooling as

well as updates for other sections.

• Chapter 9, Design of Small Forced-Air Heating and Cooling Sys-

tems, includes revised duct fitting data and new information on

duct efficiency testing. In addition, information on system perfor-

mance from Chapter 28, Furnaces, was moved to this chapter and

clarified and updated to be consistent with emerging duct effi-

ciency technology.

• Chapter 11, District Heating and Cooling, includes new informa-

tion on the effect of moisture on underground pipe insulation, cal-

culation of undisturbed soil temperatures, cathodic protection of

direct buried conduits, and leak detection. Also, the information

on consumer interconnections and metering is expanded.

• Chapter 13, Condenser Water Systems, has additional informa-

tion on water hammer, freeze protection, water treatment, over-

pressure, and free cooling.

• Chapter 16, Duct Construction, refers to new flexible duct, fiber

reinforced plastic duct, acoustical rating of duct liner, and blanket

duct insulation standards.

• Chapter 19, Evaporative Air Cooling Equipment, contains more

information on humidification and dehumidification.

• Chapter 22, Desiccant Dehumidification and Pressure Drying

Equipment, has been expanded, particularly the section on liquid

desiccant systems.

Robert A. Parsons, ASHRAE Handbook Editor

annually, enabling ASHRAE to report new data about material

properties and building physics and to promote the application of

innovative technologies.

The chapters in ASHRAE Handbooks are updated through the

experience of members of ASHRAE technical committees and

through results of ASHRAE Research reported at ASHRAE meet-

ings and published in ASHRAE special publications and in ASH-

RAE Transactions .

For information about ASHRAE Research or to become a mem-

ber contact, ASHRAE, 1791 Tullie Circle, Atlanta, GA 30329; tele-

phone: 404-636-8400; www.ashrae.org.

• Chapter 23, Air-Heating Coils, provides a broader scope of the

types of heating coils and their selection and application.

• Chapter 24, Air Cleaners for Particulate Contaminants, discusses

the new ASHRAE Standard 52.2 for testing of air-cleaning

devices and includes new sections on residential air cleaners and

bioaerosols.

• Chapter 25, Industrial Gas Cleaning and Air Pollution Control,

received a substantial update and includes revised information on

electrostatic precipitators and fabric filters,

• Chapter 26, Automatic Fuel-Burning Equipment, is updated and

now discusses low oxides of nitrogen emission from oil-fired

equipment.

• Chapter 27, Boilers, includes new information on increasing

boiler efficiency and on wall hung boilers for residential use.

• Chapter 36, Cooling Towers, has more information about (1) a

combined flow coil/fill evaporative cooling tower, (2) precau-

tions about using variable frequency drives. and (3) the increased

use and acceptance of thermal performance certification.

• Chapter 40, Motors, Motor Controls, and Variable-Speed Drives,

includes a significant new section on variable-speed drives.

• Chapter 43, Heat Exchangers, is a new chapter that provides an

overview of the topic.

• Chapter 44, Air-to-Air Energy Recovery, contains new informa-

tion on ideal air-to-air energy exchange, rating of performance,

comparison of devices, and twin tower enthalpy recovery loops.

• Chapter 46, Room Air Conditioners, Packaged Terminal Air Con-

ditioners, and Dehumidifiers, combines information from two

previous chapters.

• Chapter 47, Engine-Driven Heating and Cooling Equipment, is a

new chapter that includes information on engine-driven chillers,

air conditioners, heat pumps, and refrigeration equipment. The

chapter also includes and updates information from an old chapter

on unitary heat pumps.

This Handbook is published both as a bound print volume and in

electronic format on a CD-ROM. It is available in two editions—

one contains inch-pound (I-P) units of measurement, and the other

contains the International System of Units (SI).

Look for corrections to the 1997, 1998, and 1999 Handbooks on

the Internet at http://www.ashrae.org . Any changes in this volume

will be reported in the 2001 ASHRAE Handbook and on the ASH-

RAE web site.

If you have suggestions for improving a chapter or you would

like more information on how you can help revise a chapter, e-mail

ashrae@ashrae.org; write to Handbook Editor, ASHRAE, 1791

Tullie Circle, Atlanta, GA 30329; or fax 404-321-5478.

CHAPTER 1

HVAC SYSTEM ANALYSIS AND SELECTION

Selecting a System .......................................................................................................................... 1.1

HVAC Systems and Equipment ....................................................................................................... 1.3

Space Requirements ........................................................................................................................ 1.4

Air Distribution ............................................................................................................................... 1.5

Piping .............................................................................................................................................. 1.6

System Management ....................................................................................................................... 1.6

A tions in a space. In almost every application, a myriad of

options are available to the design engineer to satisfy this basic goal.

In the selection and combination of these options, the design engi-

neer must consider all criteria defined here to achieve the functional

requirements associated with the goal.

HVAC systems are categorized by the method used to control

heating, ventilation, and air conditioning in the conditioned area.

This chapter addresses the procedures associated with selecting the

appropriate system for a given application. It also describes and

defines the design concepts and characteristics of basic HVAC sys-

tems. Chapters 2 through 5 of this volume describe specific systems

and their attributes, based on their heating and cooling medium and

commonly used variations.

• Supporting a process, such as the operation of computer

equipment

• Promoting a germ-free environment

• Increasing sales

• Increasing net rental income

• Increasing the salability of a property

The owner can only make appropriate value judgments if the

design engineer provides complete information on the advantages

and disadvantages of each option. Just as the owner does not usually

know the relative advantages and disadvantages of different sys-

tems, the design engineer rarely knows all the owner’s financial and

functional goals. Hence, the owner must be involved in the selection

of a system.

SELECTING A SYSTEM

The design engineer is responsible for considering various sys-

tems and recommending one or two that will satisfy the goal and

perform as desired. It is imperative that the design engineer and the

owner collaborate on identifying and rating the criteria associated

with the design goal. Some criteria that may be considered are

• Temperature, humidity, and space pressure requirements

• Capacity requirements

• Redundancy

• Spatial requirements

• First cost

• Operating cost

• Maintenance cost

• Reliability

• Flexibility

• Life cycle analysis

Because these factors are interrelated, the owner and design

engineer must consider how these criteria affect each other. The rel-

ative importance of factors, such as these, differs with different

owners and often changes from one project to another for the same

owner. For example, typical concerns of owners include first cost

compared to operating cost, the extent and frequency of mainte-

nance and whether that maintenance requires entering the occupied

space, the expected frequency of failure of a system, the impact of

a failure, and the time required to correct the failure. Each of these

concerns has a different priority, depending on the owner’s goals.

System Constraints

Once the goal criteria and additional goal options are listed,

many constraints must be determined and documented. These con-

straints may include

• Performance limitations (i.e., temperature, humidity, and space

pressure)

• Available capacity

• Available space

• Availability utility source

• Building architecture

• Construction budget

Few projects allow detailed quantitative evaluation of all alter-

natives. Common sense, historical data, and subjective experience

can be used to narrow choices to one or two potential systems.

Heating and air conditioning loads often contribute to the con-

straints, narrowing the choice to systems that will fit in the available

space and be compatible with the building architecture. Chapter 28

of the 1997 ASHRAE Handbook—Fundamentals describes methods

used to determine the size and characteristics of the heating and air

conditioning loads. By establishing the capacity requirement the

size of equipment can be determined, and the choice may be nar-

rowed to those systems that work well on projects within a size

range.

Loads vary over time due to the time of day/night, changes in the

weather, occupancy, activities, and solar exposure. Each space with

a different use and/or exposure may require a different control zone

to maintain space comfort. Some areas with special requirements

may need individual systems. The extent of zoning, the degree of

control required in each zone, and the space required for individual

zones also narrow the system choices.

No matter how efficiently a particular system operates or how

economical it is to install, it can only be considered if it (1) main-

tains the desired building space environment within an acceptable

tolerance under all conditions and occupant activities and (2) phys-

ically fits into the building without being objectionable.

Additional Goals

In addition to the primary goal to provide the desired environ-

ment, the design engineer must be aware of and account for other

goals the o wner may require. These goals may include

The preparation of this chapter is assigned to TC 9.1, Large Building Air-

Conditioning Systems.

1.1

N HVAC SYSTEM maintains desired environmental condi-

1.2

2000 ASHRAE Systems and Equipment Handbook (SI)

Cooling and humidity control are often the basis of sizing

HVAC components and subsystems, but the system may also be

determined based on the ventilation criteria. For example, if large

quantities of outside air are required for ventilation or to replace air

exhausted from the building, only systems that transport large air

volumes need to be considered.

Effective delivery of heat to an area may be an equally impor-

tant factor in the selection. A distribution system that offers high

efficiency and comfort for cooling may be a poor choice for heating.

This performance compromise may be small for one application in

one climate, but may be unacceptable in another that has more strin-

gent heating requirements.

HVAC systems and the associated distribution systems often

occupy a significant amount of space . Major components may

also require special support from the structure. The size and appear-

ance of terminal devices (i.e., diffusers, fan-coil units, radiant pan-

els, etc.) have an affect on the architectural design because they are

visible in the occupied space.

Other architectural factors that limit the selection of some sys-

tems include

• Acceptable noise levels in the occupied space

• Space available to house equipment and its location relative to the

occupied space

• Space available for horizontal and/or vertical distribution pipes

and ducts

• Acceptability of components visible in the occupied space.

Construction budget constraints can also influence the choice

of HVAC systems. Based on historical data, some systems may be

economically out of reach for an owner’s building program.

Each selection may require combining a primary system with a

secondary system (or distribution system). The primary system

converts energy from fuel or electricity into a heating and/or cooling

media. The secondary system delivers heating, ventilation, and/or

cooling to the occupied space. The two systems, to a great extent,

are independent, so several secondary systems may work with a par-

ticular primary system. In some cases, however, only one secondary

system may be suitable for a particular primary system.

Once subjective analysis has identified one or two HVAC sys-

tems (sometimes only one choice may remain), detailed quantitative

evaluations must be made. All systems considered should provide

satisfactory performance to meet the owner’s essential goals. The

design engineer should provide the owner with specific data on each

system to make an informed choice. The following chapters in the

ASHRAE Handbooks should be consulted to help narrow the

choices:

• Chapter 8, 1997 ASHRAE Handbook—Fundamentals covers

physiological principles, comfort, and health.

• Chapter 30, 1997 ASHRAE Handbook—Fundamentals covers

methods for estimating annual energy costs.

• Chapter 34, 1999 ASHRAE Handbook—Applications covers

methods for energy management.

• Chapter 35, 1999 ASHRAE Handbook—Applications covers

owning and operating cost.

• Chapter 37, 1999 ASHRAE Handbook—Applications covers

mechanical maintenance.

• Chapter 46, 1999 ASHRAE Handbook—Applications covers

sound and vibration control.

Selection Report

As the last step of selection, the design engineer should prepare

a summary report that addresses the following:

•The goal

• Criteria for selection

• Important factors

• Other goals

A brief outline of each of the final selections should be provided.

In addition, those HVAC systems deemed inappropriate should be

noted as having been considered but not applicable to meet the

owner’s primary HVAC goal.

Narrowing the Choices

Chapters 2 through 5 cover building air distribution, in-room

terminal systems, central cooling and heating, and decentralized

cooling and heating. Each chapter briefly summarizes the positive

and negative features of various systems. One or two systems that

best satisfy the project goal can usually be identified by comparing

the criteria, other factors and constraints, and their relative impor-

tance. In making subjective choices, notes should be kept on all

systems considered and the reasons for eliminating those that are

unacceptable.

Table 1 Sample HVAC System Selection Matrix (0 to 10 Score)

Goal: Furnish and install an HVAC system that provides moderate space temperature

control with minimum humidity control at an operating budget of 220 kW/m 2 per year

Categories

System #1 System #2 System #3 Remarks

1. Criteria for Selection:

• 24°C space temperature with ±2°C control during occupied cycle

• 20% relative humidity with ± 5% rh control during heating season.

• First cost

• Equipment life cycle

2. Important Factors:

• First class office space stature

• Individual tenant utility metering

3. Other Goals:

• Engineered smoke control system

•ASHRAE Standard 62 ventilation rates

• Direct digital control building automation

4. System Constraints:

• No equipment on the first floor

• No exterior louvers below the perimeter windows

5. Other Constraints:

• No perimeter finned tube radiation

TOTAL SCORE

HVAC System Analysis and Selection

1.3

The report should include an HVAC system selection matrix that

identifies the one or two suggested HVAC system (primary and sec-

ondary when applicable) selections, system constraints, and other

constraints. In completing this matrix assessment, the engineer

should have the owner’s input to the analysis. This input can also be

applied as weighted multipliers.

Many grading methods are used to complete an analytical matrix

analysis. Probably the simplest grading method is to rate each item

Excellent/Very Good/Good/Fair/Poor. A numerical rating system

such as 0 to 10, with 10 equal to Excellent and 0 equal to Poor, can

provide a quantitative result. The HVAC system with the highest

numerical value then becomes the recommended HVAC system to

accomplish the goal.

The system selection report should include a summary that pro-

vides an overview followed by a more detailed account of the

HVAC system analysis and system selection. This summary should

highlight the key points and findings that led to the recommenda-

tion(s). The analysis should refer to the system selection matrix

(such as in Table 1) and the reasons for scoring.

A more detailed analysis, beginning with the owner’s goal,

should immediately following the summary. With each HVAC sys-

tem considered, the design engineer should note the criteria associ-

ated with each selection. Issues such as close temperature and

humidity control may eliminate some HVAC systems from being

considered. System constraints and other constraints, noted with

each analysis, should continue to eliminate HVAC systems. Advan-

tages and disadvantages of each system should be noted with the

scoring from the HVAC system selection matrix. This process

should reduce the HVAC selection to one or two optimum choices

to present to the owner. Examples of installations for other owners

should be included with this report to endorse the design engineer’s

final recommendation.This third party endorsement allows the

owner to inquire about the success of these other HVAC systems.

for this shortcoming. Thus, a life cycle cost analysis is very impor-

tant when evaluating central versus decentralized systems.

Operating cost. A central system usually has the advantage of

larger, more energy efficient primary equipment when compared to

decentralized system equipment.

Maintenance cost. The equipment room for a central system

provides the benefit of maintaining its HVAC equipment away from

the occupants in an appropriate service work environment. Access

to the building occupant workspace is not required, thus eliminating

disruption to the space environment, product, or process. Another

advantage may be that because of its larger capacity, there is less

HVAC equipment to service.

Reliability. Central system equipment can be an attractive ben-

efit when considering its long service life.

Flexibility. Redundancy can be a benefit when selecting standby

equipment that provides an alternative source of HVAC or backup.

Among the largest central systems are those HVAC plants serv-

ing groups of large buildings. These plants provide improved diver-

sity and generally operate more efficiently with lower maintenance

costs than individual central plants. The economics of these larger

central systems require extensive analysis. The utility analysis con-

siders multiple fuels and may also include gas and steam turbine-

driven equipment. Multiple types of primary equipment using mul-

tiple fuels and types of HVAC generating equipment (i.e., centrifu-

gal and absorption chillers) may be installed in combination in one

plant. Chapter 12, Chapter 13, and Chapter 14 provide design

details for central plants.

Decentralized System Features

Some of the criteria associated with this concept are as follows:

Temperature, humidity, and space pressure requirements. A

decentralized system may be able to fulfill any or all of these design

parameters.

Capacity requirements. A decentralized system usually

requires each piece of equipment to be sized for the maximum

capacity. Depending on the type and location of the equipment,

decentralized systems cannot take as much benefit of equipment

sizing diversity when compared to the central system diversity fac-

tor potential.

Redundancy. A decentralized system may not have the benefit

of backup or standby equipment. This limitation may need review.

Space requirements. A decentralized system may or may not

have in equipment rooms. Due to the space restrictions imposed on

the design engineer or architect, equipment may be located on the

roof and/or the ground adjacent to the building.

First cost. A decentralized system probably has the best first cost

benefit. This feature can be enhanced by phasing in the purchase of

decentralized equipment on an as-needed basis (i.e., purchasing

equipment as the building is being leased/occupied).

Operating cost. A decentralized system can emphasize this as a

benefit when strategically starting and stopping multiple pieces of

equipment. When comparing energy consumption based on peak

energy draw, decentralized equipment may not be as attractive when

compared to larger, more energy efficient central equipment.

Maintenance cost. A decentralized system can emphasize this

as a benefit when equipment is conveniently located and the equip-

ment size and associated components (i.e., filters) are standardized.

When equipment is located on a roof, maintainability may be diffi-

cult because it is difficult to access during bad weather.

Reliability. A decentralized system historically has reliable

equipment, although the estimated equipment service life may be

less than that of centralized equipment.

Flexibility. A decentralized system may be very flexible because

it may be placed in numerous locations.

HVAC SYSTEMS AND EQUIPMENT

HVAC systems may be central or decentralized. In addressing

the primary equipment location, the design engineer may locate this

equipment in a central plant (either inside or outside the building)

and distribute the air and/or water for HVAC needs from this plant.

The other option is to decentralize the equipment, with the primary

equipment located throughout the building, on the building, or adja-

cent to the building.

Central System Features

Some of the criteria associated with this concept are as follows:

Temperature, humidity, and space pressure requirements. A

central system may be able to fulfill any or all of these design

parameters.

Capacity requirements. A central system usually allows the

design engineer to consider HVAC diversity factors that reduce the

installed equipment capacity. In turn, this offers some attractive first

cost and operating cost benefits.

Redundancy. A central system can accommodate standby

equipment of equal size or of a preferred size that decentralized con-

figurations may have trouble accommodating.

Spatial requirements. The equipment room for a central system

is normally located outside the conditioned area—in a basement,

penthouse, service area, or adjacent to or remote from the building.

A disadvantage with this approach may be the additional cost to

furnish and install secondary equipment for the air and/or water

distribution. A second consideration is the access and physical

constraints throughout the building to furnish and install this sec-

ondary distribution network of ducts and/or pipes.

First cost. A central system may not be the least costly when

compared to decentralized HVAC systems. Historically, central sys-

tem equipment has a longer equipment service life to compensate

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