1、1.1CHAPTER 1HVAC SYSTEM ANALYSIS AND SELECTIONSelecting a System 1.1HVAC Systems and Equipment 1.4Space Requirements . 1.6Air Distribution 1.7Pipe Distribution 1.8Security. 1.8Automatic Controls and Building Management System 1.9Maintenance Management System. 1.9Building System Commissioning 1.9N HV
2、AC system maintains desired environmental conditionsA in a space. In almost every application, many options areavailable to the design engineer to satisfy a clients building pro-gram and design intent. In the analysis, selection, and implementa-tion of these options, the design engineer should consi
3、der thecriteria defined here, as well as project-specific parameters toachieve the functional requirements associated with the projectdesign intent. In addition to the design, equipment, and systemaspects of the proposed design, the design engineer should considersustainability as it pertains to res
4、ponsible energy and environmentaldesign, as well as constructability of the design.The integrated design process (IPD) includes members of theentire project team (e.g., owner, architect, construction team) in thedecision process. In this American Institute of Architects (AIA)-supported process, all
5、team members take part in the overall build-ing design process and, in most situations, share in project profitsand risks. For more information, refer to the AIAs Center forIntegrated Practice (CIP) at http:/network.aia.org/AIA/CenterforIntegratedPractice/Home/, or see Chapter 58 of the 2011 ASHRAEH
6、andbookHVAC Applications.HVAC systems are categorized by the method used to produce,deliver, and control heating, ventilating, and air conditioning in theconditioned area. This chapter addresses procedures for selecting anappropriate system for a given application while taking into accountpertinent
7、issues associated with designing, building, commission-ing, operating, and maintaining the system. It also describes anddefines the design concepts and characteristics of basic HVAC sys-tems. Chapters 2 to 5 describe specific systems and their attributes,based on their heating and cooling medium, th
8、e commonly usedvariations, constructability, commissioning, operation, and mainte-nance.This chapter is intended as a guide for the design engineer,builder, facility manager, and student needing to know or referencethe analysis and selection process that leads to recommending theoptimum system for t
9、he job. The approach applies to HVAC con-version, building system upgrades, system retrofits, building reno-vations and expansion, and new construction for any building:small, medium, large, below grade, at grade, low-rise, and high-rise. This system analysis and selection process (Figure 1) helpsde
10、termine the optimum system(s) for any building, regardless offacility type. Analysis examines objective, subjective, short-term,and long-term goals.SELECTING A SYSTEMThe design engineer is responsible for considering various sys-tems and equipment and recommending one or more system optionsthat will
11、 meet the project goals and perform as desired. It is imper-ative that the design engineer and owner collaborate to identify andThe preparation of this chapter is assigned to TC 9.1, Large Building Air-Conditioning Systems.Fig. 1 Process Flow Diagram(Courtesy RDK Engineers)1.2 2012 ASHRAE HandbookHV
12、AC Systems and Equipment (SI)prioritize criteria associated with the design goal. In addition, if theproject includes preconstruction services, the designer and operatorshould consult with the construction manager to take advantage ofa constructability analysis as well as the consideration of value-
13、engineered options. Occupant comfort (as defined by ASHRAEStandard 55), process heating, space heating, cooling, and ventila-tion criteria should be considered and should include the following:TemperatureHumidityAir motionAir purity or qualityAir changes per hourAir and/or water velocity requirement
14、sLocal climateSpace pressure requirements Capacity requirements, from a load calculation analysisRedundancySpatial requirementsSecurity concernsFirst costOperating cost, including energy and power costsMaintenance costReliabilityFlexibilityControllabilityLife-cycle analysisSustainability of designAc
15、oustics and vibrationMold and mildew preventionBecause these factors are interrelated, the owner, design engi-neer, and operator must consider how these criteria affect eachother. The relative importance of factors such as these varies withdifferent owners, and often changes from one project to anot
16、her forthe same owner. For example, typical owner concerns include firstcost compared to operating cost, extent and frequency of mainte-nance and whether that maintenance requires entering the occupiedspace, expected frequency of system failure, effect of failure, andtime required to correct the fai
17、lure. Each concern has a different pri-ority, depending on the owners goals.Additional GoalsIn addition to the primary goal of providing the desired environ-ment, the design engineer should be aware of and account for othergoals the owner may require. These goals may include the following:Supporting
18、 a process, such as operation of computer equipmentPromoting a germ-free environmentIncreasing marketability of rental spacesIncreasing net rental incomeIncreasing property salabilityPublic image of the propertyThe owner can only make appropriate value judgments if thedesign engineer provides comple
19、te information on the advantagesand disadvantages of each option. Just as the owner does not usuallyknow the relative advantages and disadvantages of different HVACsystems, the design engineer rarely knows all the owners financialand functional goals. Hence, the owner must be involved in systemselec
20、tion in the conceptual phase of the job. The same can be said foroperator participation so that the final design is sustainable.System ConstraintsOnce the goal criteria and additional goal options are listed,many system constraints must be determined and documented.These constraints may include the
21、following:Performance limitations (e.g., temperature, humidity, space pressure)Code requirementsAvailable capacityAvailable spaceAvailable utility sourceAvailable infrastructureBuilding architectureSystem efficiency versus energy budgetThe design engineer should closely coordinate the system con-str
22、aints with the rest of the design team, as well as the owner, toovercome design obstacles associated with the HVAC systemsunder consideration for the project.Constructability ConstraintsThe design engineer should take into account HVAC system con-tructability issues before the project reaches the co
23、nstruction docu-ment phase. Some of these constraints may significantly affect thesuccess of the design and cannot be overlooked in the design phase.Some issues and concerns associated with constructability areExisting conditionsMaintaining existing building occupancy and operationConstruction budge
24、tConstruction scheduleAbility to phase HVAC system installationEquipment availability (i.e., delivery lead times)Equipment ingress into designated spaceEquipment maintainabilityFew projects allow detailed quantitative evaluation of all alterna-tives. Common sense, historical data, and subjective exp
25、erience canbe used to narrow choices to one or two potential systems.Heating and air-conditioning loads often contribute to con-straints, narrowing the choice to systems that fit in available spaceand are compatible with building architecture. Chapters 17 and 18of the 2009 ASHRAE HandbookFundamental
26、s describe meth-ods to determine the size and characteristics of heating and air-conditioning loads. By establishing the capacity requirement,equipment size can be determined, and the choice may be narrowedto those systems that work well on projects within the required sizerange.Loads vary over time
27、 based on occupied and unoccupied periods,and changes in weather, type of occupancy, activities, internal loads,and solar exposure. Each space with a different use and/or exposuremay require its own control zone to maintain space comfort. Someareas with special requirements (e.g., ventilation requir
28、ements) mayneed individual systems. The extent of zoning, degree of controlrequired in each zone, and space required for individual zones alsonarrow system choices.No matter how efficiently a particular system operates or howeconomical it is to install, it can only be considered if it (1) main-tains
29、 the desired building space environment within an acceptabletolerance under expected conditions and occupant activities and (2)physically fits into, on, or adjacent to the building without causingobjectionable occupancy conditions.Cooling and humidity control are often the basis of sizingHVAC compon
30、ents and subsystems, but ventilation requirementsmay also significantly impact system sizing. For example, if largequantities of outdoor air are required for ventilation or to replace airexhausted from the building, the design engineer may only need toconsider systems that transport and effectively
31、condition those largeoutdoor air volumes.Effective heat delivery to an area may be equally important inselection. A distribution system that offers high efficiency and com-fort for cooling may be a poor choice for heating. The cooling,humidity, and/or heat delivery performance compromises may besmal
32、l for one application in one climate, but may be unacceptable inanother that has more stringent requirements.HVAC System Analysis and Selection 1.3HVAC systems and associated distribution systems often occupya significant amount of space. Major components may also requirespecial support from the str
33、ucture. The size and appearance of ter-minal devices (e.g., grilles, registers, diffusers, fan-coil units, radi-ant panels, chilled beams) affect architectural design because theyare visible in the occupied space.Construction budget constraints can also influence the choiceof HVAC systems. Based on
34、historical data, some systems may notbe economically viable within the budget limitations of an ownersbuilding program. In addition, annual maintenance and operatingbudget (utilities, labor, and materials) should be an integral part ofany system analysis and selection process. This is particularly i
35、mpor-tant for building owners who will retain the building for a substantialnumber of years. Value-engineered solutions can offer (1) cost-driven performance, which may provide a better solution for lowerfirst cost; (2) a more sustainable solution over the life of the equip-ment; or (3) best value b
36、ased on a reasonable return on investment.Sustainable energy consumption can be compromised andlong-term project success can be lost if building operators are nottrained to efficiently and effectively operate and maintain the build-ing systems. For projects in which the design engineer used someform
37、 of energy software simulation, the resultant data should bepassed on to the building owner so that goals and expectations can bemeasured and benchmarked against actual system performance.Even though the HVAC designers work may be complete after sys-tem commissioning and turnover to the owner, conti
38、nuous accept-able performance is expected. Refer to ASHRAE Guideline 0 and toASHRAEs Building Energy Quotient (bEQ) program (http:/ operability should be a consideration in the systemselection. Constructing a highly sophisticated, complex HVAC sys-tem in a building where maintenance personnel lack t
39、he requiredskills can be a recipe for disaster at worst, and at best requires theuse of costly outside maintenance contractors to achieve successfulsystem operation.Narrowing the ChoicesThe following chapters in this volume present information tohelp the design engineer narrow the choices of HVAC sy
40、stems:Chapter 2 focuses on a distributed approach to HVAC.Chapter 3 provides guidance for large equipment centrally locatedin or adjacent to a building.Chapter 4 addresses all-air systems.Chapter 5 covers building piping distribution, including in-roomterminal systems.Each chapter summarizes positiv
41、e and negative features of vari-ous systems. Comparing the criteria, other factors and constraints,and their relative importance usually identifies one or two systemsthat best satisfy project goals. In making choices, notes should bekept on all systems considered and the reasons for eliminating thos
42、ethat are unacceptable.Each selection may require combining a primary system with asecondary (or distribution) system. The primary system convertsenergy derived from fuel or electricity to produce a heating and/orcooling medium. The secondary system delivers heating, ventila-tion, and/or cooling to
43、the occupied space. The systems are inde-pendent to a great extent, so several secondary systems may workwith a particular primary system. In some cases, however, only onesecondary system may be suitable for a particular primary system.Once subjective analysis has identified one or more HVAC sys-tem
44、s (sometimes only one choice remains), detailed quantitativeevaluations must be made. All systems considered should providesatisfactory performance to meet the owners essential goals. Thedesign engineer should provide the owner with specific data on eachsystem to make an informed choice. Consult the
45、 following chaptersto help narrow the choices:Chapter 10 of the 2009 ASHRAE HandbookFundamentals cov-ers physiological principles, comfort, and health.Chapter 19 of the 2009 ASHRAE HandbookFundamentals cov-ers methods for estimating annual energy costs.Chapter 36 of the 2011 ASHRAE HandbookHVAC Appl
46、icationscovers methods for energy management.Chapter 37 of the 2011 ASHRAE HandbookHVAC Applicationscovers owning and operating costs.Chapter 39 of the 2011 ASHRAE HandbookHVAC Applicationscovers mechanical maintenance.Chapter 48 of the 2011 ASHRAE HandbookHVAC Applicationscovers noise and vibration
47、 control.Other documents and guidelines that should be consulted areASHRAE standards; local, state, and federal guidelines; and specialagency requirements e.g., U.S. General Services Administration(GSA), Food and Drug Administration (FDA), Joint Commissionon Accreditation of Healthcare Organizations
48、 (JCAHO), FacilityGuidelines Institute (FGI), Leadership in Energy and Environmen-tal Design (LEED).Selection ReportAs the last step, the design engineer should prepare a summaryreport that addresses the following:The originally established goalsCriteria for selectionImportant factors, including adv
49、antages and disadvantagesSystem integration with other building systemsOther goalsSecurity concernsBasis of designHVAC system analysis and selection matrixSystem narrativesBudget costsFinal recommendation(s)A brief outline of each of the final selections should be provided.In addition, HVAC systems deemed inappropriate should be notedas having been considered but not found applicable to meet theowners primary HVAC goal.The report should include an HVAC system selection matrix thatidentifies the one or two suggested HVAC system selections (pri
