documentsn.com

A room is the part of a space bounded by walls and a ceiling that is usually routinelyoccupied and served by grilles and registers to supply and recirculate or exhaustconditioned air.A ceiling plenum is a cavity within the pressure envelope that is above a room and thatis formed by a dropped lay-in ceiling and floor or roof structure above. Room walls donot necessarily extend above the dropped ceiling to the structure above.A return air plenum is a ceiling plenum with an unobstructed path to an air handlerreturn, and that contains no flammable materials or surfaces.Supply air is the all of the air delivered by the cooling/heating apparatus to the supplyair diffusers in the zone.Outdoor air, also called ventilation air, is air from outdoors that may be mixed withreturn air before passing into the cooling/heating apparatus, may be introduced to theapparatus directly before entering a zone, or in certain circumstances, may beintroduced untempered into a zone.Return air is the portion of the supply air that is recirculated after being collected by thereturn grilles in the zone.Exhaust, or exhaust air, is the portion of the supply air that is discharged from the zoneto outdoors after passing through the zone.In general, the thermal and pressure envelopes must coincide. However, if they don’t,they must be arranged so that outdoor air cannot leak into the space within the thermalenvelope – remembering that the thermal envelope generally offers no resistance to airleakage.Proceeding to the HVAC Blueprint, an OutlineThe following outline follows the organization of the chapters in this book.Gathering Information - This may be the most important part of the designer’s job.Chapter 2 discusses the types of information that are needed, what to look for, and theresponsibilities of the HVAC designer to review the data supplied and point outproblems that may adversely affect the HVAC design or the building operation. Thebase sheet should be prepared (Chapter 11) as soon as the architect’s floor plan isreceived.Preliminary Design – Decisions are made about the types of systems to be used,building zoning, equipment locations, and routing of ductwork.4

Establishing the Building Air Balance – The requirements for exhaust air and outdoorsupply air for each zone must be established prior to calculating cooling and heatingloads to ensure that the building remains under positive pressure at all times whenoccupied, and positive or neutral when unoccupied. Commercial kitchens and assemblyoccupancies present special problems. Chapter 4.Estimating Peak Cooling and Heating Loads – In many ways the easiest task, thedesigner must nonetheless subdivide the building into zones and spaces, and calculatesensible and latent cooling loads and heating loads for each. Chapter 5 is a discussion ofbuilding heat gain and loss, and Chapter 6 discusses the cooling load estimatingmethods that are the most applicable to small commercial buildings.Energy Efficient Design – Chapter 8. An outline of energy terminology and energyefficient design as prescribed by ASHRAE Standard 90.1 and suggested by goodpractice.Selecting the Primary Equipment – This is the most complex task. The coolingequipment must be matched to the sensible and latent peak loads, while at the sametime addressing part-load operation as it may affect indoor air quality and moistureproblems. Chapter 7 discusses psychrometric considerations and Chapter 9 describesmethods for selecting the cooling and heating equipment.Determining the Optimum Distribution of Supply Air – In chapter 10, a method ofdetermining the air supply to each space for each zone is described. The differencesbetween variable air volume (VAV) and constant volume systems is touched on.Determining a Control Strategy – Chapter 11. Discusses how all the equipment of aproject should be tied together to accomplish the intent of the design.Design Documents, The Blueprint – Chapter 12. The System Layout – Creating thedrawings, schedules, and specifications that fully and accurately describe the HVACdesign.Design Documents – Instructions to the Contractor – Insuring that the designdocuments convey to the HVAC contractor what the designer wants by clarifyingfeatures shown on the drawings and described in the schedules and specifications.Checking the Work – Quality Control – Chapter 13. Designers working alone areparticularly vulnerable to errors and omissions. This Chapter discusses techniques thathelp avoid mistakes.Additional useful references are: ASHRAE – Air Conditioning Systems Design Manual1and Bell – HVAC Equations, Data, and Rules of Thumb2.END5

6

Chapter 2Project Information Needed for HVAC DesignThe CommissionGenerally, the projects that are in the scope of this book are initiated by an owner – aprofessional, merchant, or church group – soliciting a proposal from an architect, whothen solicits proposals from his consultants. The mechanical engineer or designer whois responsible for the HVAC will often also be asked to design the plumbing system.However, plumbing design for small projects is largely prescriptive, meaning designparameters are fixed by the local plumbing code. For this reason, the project architectwill sometimes assume this responsibility. Fuel gas and fire suppression systemsrequire special training, and may be consigned to specialty engineers.The architect will contact his consultants, including the HVAC designer, and give them aconcept description of the project. The concept description will include as a minimumthe building size, location, number of stories, and occupancy type. Other information,such as requirements for special equipment rooms, planned functions, budgetaryrestraints, etc., may also be provided. The process starts with a phone call (or e-mailmessage), but the architect may want to meet with the consultants, singly or together todiscuss the proposed facility. From this information, the consultants will provide theirfee proposals. When the owner is satisfied with the architect’s proposal, he will give thearchitect a notice to proceed with the design. Only after this will the architect preparethe detailed documents needed by the consultants to perform their design work.DocumentsHVAC systems are necessarily applied to enclosed buildings occupied by people or byequipment requiring a controlled environment. The HVAC designer must have detailedinformation about a proposed building, which may be a stand-alone new building, anaddition to an existing building, or renovation/remodeling of an existing building orspace. The starting point for obtaining this information is the documents prepared bythe architect and other professionals involved. Comprehensively, these documents arethe architectural plans, electrical lighting plans, civil site plans, and specialty plans suchas commercial kitchen layouts.Architectural plans include all of the following: floor plans, elevations, wall sections,building sections, window and door schedules, and room schedule. Figures 2-1, 2-2,and 2-3 show a typical architectural plan with schedules, wall sections, and elevations.Floor plans (Figure 2-1) show the building orientation and layout, area of spaces androoms, basic room use (office, classroom, restroom, etc), and location of windows anddoors. Also needed are the locations of heat-producing equipment such7

Architectural plans, elevations, and sections by Tock Ohazama, Architect, Tallahassee, FloridaFigure 2-28

as vending machines, copiers, and large servers. Floor plans also often include afurniture layout that will help the HVAC designer determine occupancy patterns. Roofplans may be needed for the HVAC designer to coordinate rooftop equipment, piping,and ductwork. Window and door schedules are keyed to the architectural plan and listwindows and doors with size, type, and glazing. Room schedules show room wall andceiling finishes, and ceiling heights for each numbered room.Architect’s plans mayalready include space forair conditioning airhandlers, based on thearchitect’s idea of howmuch space should berequired. The allocatedspace may be inadequate,and the designer willneed to coordinate thiswith the architect duringpreliminary design.Elevations (Figure 2-2)show the relationshipbetween various elementsof the building, and canbe used to find the size ofwindow and dooropenings in lieu of aschedule. It is importantthat the designer have acomplete definition of theglazing and fenestration,and this information mayhave to be requesteddirectly from the architectduring preliminarydesign.Figure 2-3Wall sections (Figure 23), including sectionsthrough the building roof and floor assemblies, provide essential information about thebuilding envelope – thermal conductivity and reflectivity of opaque materials, andlocation and thickness of building insulation. Window and door schedules give the sizeof building openings, and the type of window or door (i.e. insulated, storefront, etc).Building sections such as Figure 2-4 show the designer how the roof-ceiling and floorceiling assemblies are constructed, and what clearances and routes willbe availableforFigure2-29

supply and return ducts or plenums. Combined with wall sections, they also show theboundaries of the thermal and pressure envelope of the building.Electrical lighting plans will show the location and number of lighting fixtures, coded toan accompanying fixture schedule. With very simple jobs, especially when the HVACdesigner and lighting designer have worked together before, the fixture plan andschedule may be dispensed with, and a lighting power density (watts/sq ft) substituted.The designer must also find out the electrical service voltage and phase,using the electrical power plan or directly from the electrical designer.Figure 2-4If a commercial kitchen is included in the project, the HVAC designer will need to sizethe grease hood ventilation equipment and the dishwasher and scullery exhaust in thecontext of the total building ventilation balance, and evaluate the cooling load of thecooking equipment. To do this requires a detailed kitchen equipment layout, with allequipment coded to a schedule describing each item and providing, especially, the fueltype and heat input to that item.Civil site plans are needed for the designer to coordinate the location of exteriorequipment , piping, and ductwork (except for rooftop), and to ensure code compliancewith building air intakes and exhausts.Data InputsIt was mentioned above that the designer needs to know the location and heatdissipation of heat-producing equipment such as vending machines, copiers, and largeservers. This data is often not included on floor plans, and must be solicited directlyfrom the owner or building designer. Also needed is any special ventilation required,either by request of the owner or intrinsic to particular equipment.10

Floor plans usually have a generic description of the use of each interior space, but nospecific information about occupancy load. Often, standards such as ASHRAE 62(Chapter 4) may be used to estimate occupancy load, but it is always best to confirmexpected peak normal occupancy of each space with the owner or building designer.The HVAC designer must decide what sensible and latent loads to assign to occupantsbased on the space description and his experience. Tables in the ASHRAE Handbook –Fundamentals, will also give guidance on occupant cooling loads.Restroom and shower areas are completely exhausted by code in Florida and mostother jurisdictions, and thus do not contribute directly to heating or cooling loads.However, the exhaust is inevitably made up by outdoor air introduced into the buildingeither across a cooling coil, by un-tempered mechanical supply, or by infiltration. Ofcourse, it is therefore necessary for the HVAC designer and the HVAC contractor toknow where restroom and shower plumbing fixtures are located. This information isusually found on the floor plan, but if it is not, must be solicited from the buildingdesigner. Exhaust requirements are discussed in Chapter 4.The HVAC designer, in collaboration with the building designer and owner, establishesthe indoor design conditions for the building – dry bulb temperature and relativehumidity. However, outdoor design conditions must be based on local weather data.Weather data is available in many HVAC computer design programs, and in tabularform in the ASHRAE Handbook – Fundamentals. (Beginning with the 2005Fundamentals detailed weather information for US and worldwide sites is availableonly on the CD, not in the printed Handbook.) HVAC designers often adjust this databased on local site conditions and personal experience.Design weather data tables are available for most U.S. Cities, as well as for most cities ofany size anywhere in the world. Chapter 6 discusses ways to use the data forcalculating cooling, heating, and dehumidification loads.Review of InformationUpon receipt of the documents and information needed as outlined above, it is theresponsibility of the HVAC designer to review the submitted information in detail, andto notify the building designer of possible problem areas. Typical problems are gaps inthe pressure envelope (allowing paths for tramp air to leak into the thermal envelope),large uninsulated or un-tinted glass areas, inadequate building insulation, inadequatespace to run ductwork or install equipment, configurations that may violate the localmechanical or energy code, and conditions that may compromise indoor air quality.Codes, Standards, and ReferencesFamiliarity with the following documents is essential to execute a successful design.Local Building Codes : These are the basic codes that the local building officials will useto review proposed projects and inspect work in progress. Most codes are now11

available on CD through the local building department – examples are the FloridaUnified Building Code, the Southern Standard Building Code, and the National BuildingCode. Each jurisdiction adopts a code that suits it, and often supplements the adoptedcode with special provisions. All codes include special sections for Buildings, Plumbing,Mechanical, Fuel Gas, and Energy Compliance. The designer should be familiar with thesections of the code applicable to his work, and should have a copy available forreference during the design process. HVAC design will be governed by the BuildingCode, the Mechanical Code, the Fuel Gas Code, and the Energy Code sections. Of course,the Building Code covers items generally of importance to the architect, but manyBuilding Code sections have a direct effect on HVAC design, such as those pertaining tofire separation and means of egress.National Fire Protection Association (NFPA) Standards : The HVAC designer will notneed a complete set of NFPA standards. For one thing, many of the NFPA standards areincorporated into the local codes. However, a few of the standards should be availablefor reference by the designer, even though many of the requirements may beincorporated into local codes. These are NFPA 70 “National Electric Code”, NFPA 90Aand 90B which apply to the installation of HVAC systems, and NFPA 96 Standard forVentilation Control and Fire Protection of Commercial Cooking Operations3.Standards of the American Society of Heating, Refrigerating, and Air ConditioningEngineers (ASHRAE) : The ASHRAE Handbook of Fundamentals4 is referred to often inthis book, and the designer should have the latest edition available for ready reference.Important standards to have available in the latest edition for ready reference areStandard 62.1 Ventilation for Acceptable Indoor Air Quality5, Standard 90.1 EnergyStandard for Buildings Except Low Rise Residential Buildings6 and the Standard 62.1User’s Manual7. Standard 52.28 which defines air filter standards, Standard 55“Thermal Environmental Conditions for Human Occupancy”9,All of the publications referenced are updated on three to five year cycles. The latestupdate at the time a project is started should be the one used for reference. The latestupdate at the time of publication of this book is shown in the references.SummaryBefore beginning any HVAC project, the designer must have a comprehensive set ofdocuments and data that completely define the building and the local environment.This usually means a complete and final set of architectural drawings, lighting layouts,civil site plans, internal loads, occupancy patterns, and design points for the spaces andoutdoors. In the absence of complete information, and under pressure to deliver adesign, the designer may estimate many parameters based generic rules of thumb andon past experience with the building and lighting designers. However, this is risky, andcould result in inadequate design, over design, or re-doing many design tasks.The HVAC designer has the responsibility to review the documents and data for theproject, and to inform the building designer of any problems he perceives.12

The HVAC designer should maintain a design file stating all the assumptions made for aproject, the rationale, and all correspondence with the other designers and with theowner.END13

Chapter 3Preliminary Design – PlanningDecisions to be MadeOnce all of the data about the proposed building project has been obtained andreviewed, the designer is ready to make some basic decisions about how the system willbe configured. These decisions must be made in collaboration with the owner and thearchitect. The owner will have budgetary constraints and will want input into the typeof systems to be used. The architect will expect the HVAC system to be compatible withhis vision for the building, and will have to provide for spaces for placement of theequipment.Preliminary design is an essential step in the design process, but does not need to be adetailed or drawn-out task and is generally not formalized for the projects that are thesubject of this book. However, it provides an opportunity for the engineer to outline forthe owner and architect his response to their requirements, and what he plans toinclude in his design.This means that the designer must decide what ambient outdoor conditions to use. Hemust also decide how the building will be zoned and what kind of corerefrigerating/heating equipment, air handlers, and terminal systems will be used beforeknowing what the building loads will be. Detailed selection of equipment is discussedin Chapter 9, after the cooling and heating loads have been estimated and the room andcoil psychrometrics are known. However, the architect, engineer, and owner mustagree on the general outline of the HVAC configuration to avoid errors as the projectunfolds. This outline should be as detailed as possible and should be submitted to thearchitect in writing as a basis of design report. The design report should be updatedregularly to reflect changes made as the project progresses.The Design Day and Hour – Outdoor Ambient Design ConditionsPart of the project information is the precise location of the proposed building. Thecooling and dehumidification loads will have to be based on either the day with thehighest dry bulb temperature or the highest wet bulb temperature. For cooling loadcalculations, this book will use dry bulb temperature as the design standard. Forselecting air pre-treatment systems (chapter 9), most authorities recommend using wetbulb temperature as the standard. The reason for this latter will be found in Chapter 9.ASHRAE, among other sources has extensive weather data covering all of the UnitedStates and much of the rest of the world. A synopsis will be found in the 2009Fundamentals handbook, Chapter 14, “Climatic Design Information”. Complete tablesfor most U.S. and World Cities is found in the Fundamentals handbook CD, or is15

available separately from ASHRAE. The reference in handbook Chapter 14 includes atable of complete design conditions for a single location, Atlanta, Georgia, plus basicdesign conditions for all weather stations in the U.S. and most large world cities. Thesetables provide the statistical occurrence of the maximum values of the followingparameters at .4%, 1%, and 2% of annual hours:DBMCWBWBMCDBmaximum dry bulb temperaturemean coincident wet bulb temperature (coincident with themaximum dry bulb temperaturemaximum wet bulb temperaturemean coincident dry bulb temperature (coincident with WB)For example, the maximum dry bulb temperature at .4% would be exceeded in only 35hours of a typical year. In humid climates, the summer condition of WB/MCDB willusually be at a higher enthalpy than the condition o

Chapter 11 – HVAC Controls and Indoor Air Quality 103 Basics of Indoor Air Quality Control The Basic HVAC Control Automatic Time of Day Control Humidity Control Reheat Dedicated DX Outdoor Air Unit Chapter 12 – Design Drawings, Specifications, Notes, and Schedules – Th