contentsIntroduction 2Early Design Issues 4Zone Issues 7VAVBox Selection and Controls 8Duct Design 10Supply Air Temperature Control 14Fan Selection 15Supply Air Pressure Reset 18Coils and Filters 20Outside, Return, andExhaust Air Control 21Notes and AdditionalInformation 25SummaryThis Advanced VAV System Design Brief providesrecommendations to help engineers improve the efficiency oflarge HVAC systems. It focuses on built-up variable-air-volume(VAV) systems in multistory office buildings.The recommended measures promote efficient, practicaldesigns that advance standard practice, achieve cost-effectiveenergy savings, and can be implemented using currenttechnology. Here are some of the key recommendations:■ Reduce design system static pressure■ Employ demand-based static pressure reset■ Use low-pressure plenum returns/relief fans■ Employ demand-based, supply temperature reset to reducereheat energy and extend economizer effectiveness■ Design fan systems to turn down and stage efficiently■ Size terminal units to balance energy impacts of pressuredrop and minimum airflow control■ Set terminal unit minimums as low as required forventilation and use intelligent VAV box control schemes toprevent stratification■ Employ demand-based ventilation controls for high-densityoccupancies■ Design conference rooms to provide ventilation withoutexcessive fan energy or reheatOf all the recommendations in this Design Brief, VAV boxcontrol and supply air pressure reset often have the largestimpact on system efficiency. Design engineers are encouragedto pay particular attention to these two issues.energydesignresourcesADVANCED VARIABLE-AIR-VOLUME (VAV) SYSTEMSMany large HVAC systems usesignificantly more energy thannecessary. Design engineers canimprove the efficiency and costeffectiveness of built-up VAV systemsby following recommendations thatemphasize integrated design anddesigning for the full range ofsystem operation.design briefIntroductionThis Design Brief provides an authoritative new resource forheating, ventilation, and air-conditioning (HVAC) designers. Itpresents the most current recommendations on variable-air-volume (VAV) airside system design, and provides brand-newinformation on fan selection and modeling.The recommended measures incorporate findings from a recentstudy of built-up VAV systems conducted for the CaliforniaEnergy Commission. That three-year study, which included fieldmonitoring of five large office buildings in California, resulted inthe publication of the Advanced VAV System Design Guide,which presents a more comprehensive version of therecommendations in this Design Brief.1Both publications—this Design Brief and the full DesignGuide—focus on built-up VAV systems in multistory officebuildings in California or similar climates (California has 16climate zones). But much of the information is useful for a widerrange of system types, building types, and locations. The recommendations in this Design Brief address airside systemdesign, with an emphasis on getting the air distribution systemcomponents to work together in an integrated fashion. Of all therecommendations in this Design Brief, VAV box control (section3) and supply air pressure reset (section 7) will have the largestimpact on system performance. Design engineers are encouragedto pay particular attention to these two topics. Figure 1 provides an overview of all the topics covered in thisDesign Brief. Market ShareOver the next 10 years, about 30 million square feet per year oflarge office buildings will be constructed in California, equal to20 percent of new construction in the state. Approximately one-half of those buildings will be served by VAV reheat systems.Therefore, the recommendations in this Design Brief will applyto roughly 150 million square feet of new buildings built in the10-year period between 2003 and 2012. This equals roughly 10percent of the total commercial construction forecast.PAGE 2 ADVANCED VAV SYSTEM DESIGN BRIEFPAGE 3ADVANCED VAV SYSTEM DESIGN BRIEFWhile chilled water systems account for only about 4 percent of theHVAC systems in commercial buildings, they account for as muchas 45 percent of the statewide cooling capacity. And chilled watersystems with VAV reheat—the type of system addressed by thisDesign Brief—are estimated to account for slightly more than 20percent of all cooling capacity. Clearly, the performance of thesesystems has a tremendous ability to affect statewide energy use.Following the practices in this Design Brief can lead to majorimprovements in system performance, energy efficiency, andoccupant comfort.2. ZONE ISSUES Design of conference rooms3. VAV Box Selection VAV box selection summary VAV reheat box control Minimum volume setpoints Sizing VAV reheat boxes Other box types Other issues4. DUCT DESIGN General guidelines Supply duct sizing Return air system sizing Noise control6. FAN SELECTION Fan selection criteria Visualizing fan performance8. COILS & FILTERS Construction filters Pre-filters Final filter selection Filter area Extended surface area filters Coil selection Coil bypass9. OUTSIDE, RETURN & EXHAUST AIR CONTROL Control of minimum OSA for VAV Design of airside economizer systems Economizer temperature control Economizer high-limit switches5. SUPPLY AIR TEMPERATURE CONTROL Optimal temperature Sequence of operations1. EARLY DESIGN ISSUES Role of simulation in design Location and size of airshafts Return air system Auxiliary loads Design airside supply temperature Determining internal loads Integrated design7. SUPPLY AIR PRESSURE RESET Static pressure sensor location Demand-based SP setpoint reset Fan operation and isolationFigure 1: Overview of Design Brief ContentsThis Design Brief is organized around key design considerations and components that affect the performance of VAV systems.These practices can lead tomajor improvements in systemperformance, energy efficiencyand occupant comfort.PAGE 4 ADVANCED VAV SYSTEM DESIGN BRIEFEarly Design IssuesThe old adage, “An ounce of prevention is worth a pound ofcure,” certainly holds true for the design of built-up VAVsystems, which are complex custom assemblies. Extra timecarefully spent in early design can save weeks of time later inthe process. It can also help improve client relations and reduceconstruction and operating costs. Below is a short list of early design issues
View Full Document
Unlocking...