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© 2011 The Academy of HVAC Engineering Ltd. This PDF is made available for personal use only, subject to the signed agreement. Any other use requires prior written consent from the copyright owner. Unauthorized use, reproduction and/or distribution are strictly prohibited and violate applicable laws. All rights reserved.
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Contents Guide overview……………………………………………………………………….……………………………
5
1
General design criteria …………………………………………………………………...................................
7
2
Identifying space occupancy and heat gain sources ……………………………..….................................
8
3
Design climate conditions ……………………………………………………………….................................
10
4
Design indoor comfort conditions ………………………………………………….….………………………...
15
5
Space noise criterion ………………………………….…………................................................................
6
Selection of air-conditioning system concept ………………………………………………………………….
22
7
Comfort zoning ……………………………………..……………….…………………..………………………..
29
8
Calculation of the space ventilation air requirements..…………..………………..………………………….
31
9
Envelope thermal performance….…………………………………………………..….………………………
34
20
10
How to calculate the space heat losses…………………………………………..….………………………...
39
11
How to calculate the space cooling loads……………………………………………………………………...
45
11.1
The wall and roof cooling loads………………………….……………………………………………………...
47
11.2
The cooling loads from windows………………………………………………………………………………..
51
11.3
The cooling loads from lighting and office equipment………………………………………………………..
56
11.4
The occupant cooling loads…………………………………………………………………………………….
56
11.5
Total space cooling loads……………………………………………………………………………………….
57
12
How to calculate the space supply airflow rate…………..…………….……………………………………..
58
13
How to calculate the zone supply airflow rate……………………………...………………………………….
60
14
How to calculate the system supply airflow rate…………………………………..………………………..…
63
15
How to calculate the system-level outdoor airflow requirements…..……….……………………………….
64
16
Sizing of the space air diffusion outlets …………….………………..………………………………………..
67
17
Sizing of the ductwork …….……….………………………..…………..……………………………………....
72
18
Sizing of the supply air fan …………………………………………………….…..……………………………
79
19
Configuring the air-handling unit………………………………………………………………………………..
87
20
The basics of psychrometric analysis ……………………..………………..………………………………..
90
21
Sizing of the central cooling coil……………………………………………………………………………….
92
22
Sizing of the central heating coil and humidifier……………………………………………………………...
101
23
Sizing of the zone and space heating units………………………………………….………………………..
106
24
Sizing of the heating plant…………….………………………………………………………………………..
110
24.1
Calculation of the heating plant output………….…………………….………………………………………
111
24.2
Sizing of the boilers……….……….…………………..……………………………………………………….
113
24.3
Sizing of the hot water piping……………….………………………………………………………………….
116
24.4
Sizing of the expansion tank……………………………………………………………………………………
119
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24.5
Sizing of the heating pumps…………………………………………………………………………………….
120
25
Development of the air-conditioning system controls concept.…………………………………………….
122
26
Development of the HVAC drawings………………………………………………………………………….
126
27
Example of the air-conditioning system design process………………...…………………………………...
127
References Tables R-1 to R-27 from ASHRAE Handbook Fundamentals, 2005……………………………………...
168
Tables R-28 and R-29 from ASHRAE Standard 55-2004…………………………………………………..
185
Tables R-30 and R-33 from ASHRAE Standard 62.1-2007…………………………………………………
187
Tables R-34 to R-41 from ASHRAE Standard 90.1-2007…………………………………………………..
191
Table R-42. General Design Criteria for Commercial and Public Buildings……………………………….
196
Appendix A. Imperial to Metric Unit Conversion Factors…………….……………………………………….
197
Appendix B. Validation of the HVAC Engineering Book
198
Spreadsheets……………………............................... Appendix C. HVAC Drawings for the Sample Building……………………………………………………….
200
Appendix D. “DESIGN LOADS” Spreadsheet’s Reports for the Sample
211
Building………………………………. Appendix E. “AIRFLOW” Spreadsheet’s Reports for the Sample
220
Building………………………………………. Appendix F. “WATERFLOW” Spreadsheet’s Reports for the Sample
221
Building…………………………………. Nomenclature ………………………………………………………………………………...........................
223
ASHRAE Publications…………………………….……………………..……………………………………….
226
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Guide overview Originally, this guide was developed to assist junior mechanical engineers in learning the most challenging aspect of central air-conditioning systems design- the streamlined calculations governing the entire design process. The current edition of this guide expanded its original scope with the system’s arrangement, control principles, and drawings development. Some of the chapters and examples have been revised for better clarity. The original guide name “The HVAC Engineering Book” has been changed to avoid confusion while referencing to the supporting E xcel spreadsheet suite having similar name. ASHRAE handbooks present broad overviews of many, often alternative, calculation and design methods. A junior engineer will be totally lost trying to figure out which of the methods to use and at what stage. The guide constructs the most suitable and commonly used methods and routines from the ASHRAE handbooks, standards and other sources into a system of interrelated computations and graphical works. The design process is supported by:
A toolkit of Excel spreadsheets
Reference tables from ASHRAE handbooks and standards (courtesy of ASHRAE)
Online climatic database from ASHRAE Weather Tables (courtesy of ASHRAE)
Other online supporting materials. Traditionally, HVAC engineering practices have included notebooks filing all calculation worksheets to
support the HVAC drawings and specifications. The spreadsheets serve the same purpose: they carry out the calculations and keep track of the calculation inputs and outputs in electronic format. The toolkit of spreadsheets has title The HVAC Engineering Book©. The Toolkit includes the following spreadsheets:
THERMAL COMFORT- for prediction of thermal comfort at various indoor conditions
DESIGN LOADS- for calculating thermal loads of air-handling and terminal units
AIRFLOW- for calculating duct and air diffusion systems
WATER FLOW- for calculating piping systems
PSYCHROMETRICS- for calculation of the full set of moist air properties. Existing computer HVAC related programs conceal their algorithms and interim calculation results,
often causing inadequate input data entry and misinterpretation of the outputs. To avoid these shortcomings, the Toolkit organizes the calculations in interlinked electronic worksheets - tabs, placed in the order of the design progress. The tabs expose the majority of the calculations accompanied by formula descriptions. You have the option of integrating the Toolkit spreadsheets with your own existing s preadsheets. The spreadsheets were tested against the examples in ASHRAE Fundamentals, 2005 /1/ and standard /5/. The test results are presented in A ppendix B. The spreadsheets allow for design of constant and variable air volume systems with up to 50 individual comfort zones. © 2011 The Academy of HVAC Engineering Ltd. This PDF is made available for personal use only, subject to the signed agreement. Any other use requires prior written consent from the copyright owner. Unauthorized use, reproduction and/or distribution are strictly prohibited and violate applicable laws. All rights reserved.
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Chapters 1 to 26 describe the e ntire design process. The examples, at the end of each chapter, illustrate the described methods. To demonstrate complicated and laborious routines, the examples use relevant Toolkit spreadsheets and the HVAC drawings of a sample building in the drawing M-1A of Appendix C. The exemplar of the entire design process in Chapter 27 will guide you how to apply the described methods for design of a constant volume air-conditioning system serving the sample building. The Toolkit spreadsheets’ reports summarizing the calculation results for the sample building can be viewed at Appendices D, E, and F. Some of the reference tables are replicated i n the “Lookups” tabs of the spreadsheets. The tables gathered in the “References” section of this guide are not presented in full vol ume: they can be used for learning purposes only. For real design, the source handbooks and standards are to be approached. The sequence and interconnection of the engineering routines and calculations is an important part of the professional knowledge, fluent command of which makes the HVAC engineer confident about solving various tasks. Existing courses target only parts of the design, making it difficult to picture the entire design process. To overcome this shortcoming, the guide systemizes the design steps in a general sequence outlined below: 1.
Establish general system design criteria
2.
Gather building and space related data
3.
Establish design outdoor and indoor air conditions
4.
Develop the system design concept
5.
Calculate the space ventilation air requirements
6.
Calculate the space thermal loads and air supply requirements
7.
Calculate the zone-level air supply requirements
8.
Calculate the system-level outdoor and supply air requirements
9.
Size the air distribution system and fans
10. Size the air-handling unit components 11. Size the zone and space terminal units 12. Size the boiler plant and hot water piping 13. Develop the HVAC controls strategies 14. Develop the drawings
The sequence illustrates where the design starts and where it ends. The general design process remains mainly the same regardless of the system type and building category. As you can see, the majority of the engineer’s work is calculations. However, memorizing the numerous formulas that constitute the design process would be a poor learning approach. Instead, adopting the engineering reasoning and the formulae logic is much more productive. This approach gives you clear
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understanding of the variables involved in the HVAC system design and their impact on the design results and the ability to design virtually any types of air-conditioning systems. Many existing HVAC software tools employ the methods described in this book. The understanding of the calculation methods will allow you to efficiently use the existing and emerging software tools in your professional practice. Numerical values in this guide are given in both IP (Inch-Pound) and SI (Metric) units, while the examples and figures are in IP units only. The main unit conversion factors can be viewed in Appendix A. The chapters of the guide will explain the design procedures in the order of the general flow of the design process as outlined in the sequence above.
Chapter 1. General design criteria 1 2 3 4 5 6 7
Establish general system design criteria Gather building and space related data Establish design outdoor and indoor air conditions Develop the system design concept Calculate the space ventilation air requirements Calculate the space loads and air supply requirements Calculate the zone-level air supply requirements
Design Progress 8 Calculate the system-level outdoor and supply air requirements 9 Size the air distribution system and fans 10 Size the air-handling unit components 11 Size the zone and space terminal units 12 Size the boiler plant and hot water piping 13 Develop the HVAC controls strategies 14 Develop the drawings
Get familiar with the standards governing the design process
Air-conditioning systems must meet a number of criteria set forth by industry standards, building codes, and other documents. Usually, local building codes in Canada and The USA are based on the following standards:
ASHRAE Standard 55-2004 /5/ sets forth design indoor conditions
Design climatic data from appropriate building code or ASHRAE Weather Tables /1/
ASHRAE Standard 62.1-2007 /6/ determines ventilation air volume requirements for various occupancy categories
ASHRAE Standard 90.1-2007 /7/ sets forth the envelope, lighting, and HVAC equipment performances to minimize the building energy consumption
ASHRAE Standard 134-2005 /8/ lists the HVAC related symbols recommended for use in the course of the drawings development.
Each occupancy category requires a certain combination of indoor air temperature, humidity, and other factors together providing the most productive and healthy indoor environment. The standard /5/ identifies the indoor comfort parameters affecting the occupant thermal comfort. The standard describes a general method of thermal comfort prediction accounting for variations in the occupant metabolism rate, clothing insulation, and other factors i mpacting thermal comfort. The ultimate goal of the standard is to © 2011 The Academy of HVAC Engineering Ltd. This PDF is made available for personal use only, subject to the signed agreement. Any other use requires prior written consent from the copyright owner. Unauthorized use, reproduction and/or distribution are strictly prohibited and violate applicable laws. All rights reserved.
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determine the combination of the indoor air parameters that the air system has to be ab le to maintain. Further this set of parameters, mainly air temperature and relative humidity, will be called design indoor conditions. The design climatic data provide the “worst” weather conditions (ambient temperature, humidity, solar flux etc.) at which the HVAC system at han d must be capable of maintaining the design indoor conditions. Further we will call these parameters “design climate conditions”. The climatic database replicated from the Weather Tables /1/ can be viewed at www.hvac-academy.com. Building synthetic materials and occupants are the primary sources of air contamination in public and institutional buildings. The standard /6/ introduces the methods determining the space ventilation ai r volume requirements sufficient to keep the indoor air contamination at an acceptable level. Noise generated by HVAC systems is another important characteristic of the indoor environment. Acceptable noise level varies depending on the space occupancy. For example, the acceptable noise level for performing art halls is much lower than for concession areas of movie theatres. The noise level of certain space categories is regulated by appropriate authorities. You can establish the acceptable noise level criterion for public and commercial buildings by using Table R-42. Soaring energy costs have forced governments and buildi ng owners to design buildings with low energy use. The standard /7/ stimulates the engi neers to design energy efficient HVAC and li ghting systems and building envelopes of high thermal resistance. The mechanical drawings of HVAC systems use special graphical symbols to describe the system layout and characteristics. To avoid misinterpretation of the drawings, the standard /8/ provides the lists and definitions of HVAC-related symbols recommended for development of mechanical drawings. If you design an HVAC system not compliant with the requirements of the standards above, the system will not be permitted for construction.
Chapter 2. Identifying space occupancy and heat gain sources 1 2 3 4 5 6 7
Establish general system design criteria Gather building and space related data Establish design outdoor and indoor air conditions Develop the system design concept Calculate the space ventilation air requirements Calculate the space loads and air supply requirements Calculate the zone-level air supply requirements
Design Progress 8 Calculate the system-level outdoor and supply air requirements 9 Size the air distribution system and fans 10 Size the air-handling unit components 11 Size the zone and space terminal units 12 Size the boiler plant and hot water piping 13 Develop the HVAC controls strategies 14 Develop the drawings
Learn the building and space related data required to size HVAC system
HVAC systems assimilate the heat, moisture, airborne particles, and other pollutants produced b y building occupants and penetrated through the envelope. Identification of the pollutant sources and their © 2011 The Academy of HVAC Engineering Ltd. This PDF is made available for personal use only, subject to the signed agreement. Any other use requires prior written consent from the copyright owner. Unauthorized use, reproduction and/or distribution are strictly prohibited and violate applicable laws. All rights reserved.
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emission rates is the first step of the HVAC system design. In commercial, institutional and public buildings the main source of air p ollution is the heat generated by the occupants, office equipment, appliances, and lighting. The occupants extract heat in proportion to their activity level. For example, a dancing person produces 850 Btu/h (250W) of sensible and latent heat, whereas a theatre spectator gives up only 350 Btu/h (100W). The occupant activity level and the maximum number of occupants per space can be identified using the space’s name and furniture layout shown on the architectural drawings. If the furniture layout is not available, the occupant number can be estimated based on the maximum occupant density per unit of floor area as presented in Table R-30 for various space categories. You can also use the architectural drawings to identify the type and layout of the space equipment (computers, copier machines, etc.) and lighting fixtures. Tables R-5 and R-6 will help you to determine the equipment heat production rates. The total heat production rates from occupants and equipment are calculated in proportion to the n umber of occupants and the number of equipment units i n the space. Determine the space lighting power demand by multiplic ation of the number of lighting fixtures shown on the architectural drawings by the power input of one fixture. For example, a common T-8 fluorescent twobulb 4ft fixture has a power input of approximately 50W. If the lighting layout is not available, use the lighting power density per unit of floor area from Table R-41. If the space has a distinctive dai ly occupancy profile, estimate the occupant, equipment, and l ighting time-of-day uses as a percentage of the associated total heat production rates. The external sources of heat in spaces are direct and diffuse solar radiation penetrating through windows and the heat transferred by conduction through the exterior walls, roof, and other opaque structural elements. The exterior walls, roof, and window arrangements are shown on the architectural drawings. You will use this information to calcula te the heat flow rates transferring through the envelope. Find the North direction shown on the drawing title. It indicates the position of the building on the Earth. This information will be required to calculate the solar heat gain rates from the walls and windows with different orientation. Position of the lighting fixtures in relation to the suspended ceiling is another characteristic identified from the drawings. If lighting fixtures are of a suspended type (to the left picture in Figure 1), all the ligh ting heat enters the air-conditioned space below the ceiling.
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