A Study of the Thermal Comfort and Ventilation Performance of an Underfloor Air Distribution System PDF Download
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Author: Jae D. Chang
Publisher:
ISBN:
Category :
Languages : en
Pages : 362
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Author: Jae D. Chang
Publisher:
ISBN:
Category :
Languages : en
Pages : 362
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Author: Fred S. Bauman
Publisher: Bibliotheca Press
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 260
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This guide is ideal for HVAC design engineers, architects, building owners, facility managers, equipment manufacturers and installers, utility engineers, researchers, and other users of underfloor air distribution (UFAD) technology. UFAD systems are innovative methods for delivering space conditioning in offices and other commercial buildings. Improved Thermal Comfort, Improved Ventilation Efficiency and Indoor Air Quality, Reduced Energy Use and Reduced Life-Cycle Building Costs -- The guide explains these as some of the advantages that UFAD systems have over traditional overhead air distribution systems. This guide provides assistance in the design of UFAD systems that are energy efficient, intelligently operated, and effective in their performance. It also describes important research results that support current thinking on UFAD design and includes an extensive annotated bibliography for those seeking additional detailed information.
Author: Yoon Soo Lee
Publisher:
ISBN:
Category :
Languages : en
Pages : 216
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Author: Ulf Larsson
Publisher: Linköping University Electronic Press
ISBN: 9176852512
Category :
Languages : en
Pages : 108
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People nowadays spend most of their time indoors, for example in their homes, cars, in trains, at work, etc. In Sweden, the energy demand in the built environment is a growing issue. The building sector accounts for 40% of total energy use and 15% of total CO2 emissions, and around one-third of the energy use in the world is related to providing a healthy and good comfort indoors. To achieve acceptable indoor climates new designs for the ventilation systems have been proposed in recent decades, among them stratified ventilation systems. Stratified ventilation is a concept that often allows good performance for both indoor air quality and thermal comfort. Stratified ventilation systems are effective in reducing cross contamination, since there is virtually no mixing in the space; the temperature and the pollutant concentration increase linearly from the heat source with the height of the occupied zone. There are many different ventilation supply devices using the stratified principle, such as displacement supply device (DSD), impinging jet supply device (IJSD) and wall confluent jet supply device (WCJSD). The main aim of this thesis is to analyze and compare different supply devices based on stratified ventilation, with different setups, related to thermal indoor climate, energy efficiency and ventilation efficiency. The ultimate goal is to contribute to an increased understanding of how ventilation systems with stratified supply devices perform. Two scientific methods have mainly been used in this thesis, i.e., experimental and numerical investigations. For numerical experiments the CFD (Computational Fluid Dynamics) code ANSYS and FIDAP have been used. Experimental studies have been performed with thermocouples, Hot-Wire Anemometry (HWA) and Hot-Sphere Anemometry, thermal comfort measurement equipment and tracer gas measurement equipment. This thesis mainly focuses on three research questions: Interaction between a supply device based on stratified ventilation and downdraft from windows; Flow behavior, energy performance and air change effectiveness for different supply devices based on stratified ventilation; and Thermal comfort for different supply devices based on stratified ventilation. Research question one showed that the arrangement of displacement supply device and window in cold climate has significant effect on the flow pattern below the window. Different supply airflow rates have an effect on both the velocity and the temperature of the downdraft. In this case the velocity decreased by approximately 9.5% and the temperature in the downdraft decreased 0.5°C when the flowrate from the supply device increased from 10 to 15 l/s. Research question two showed that airflow patterns between different air supply systems were essentially related to characteristics of air supply devices, such as the type, configuration and position, as well as air supply velocities and momentum. For WCJSD, IJSD and DSD, positions of heat sources (such as occupant, computers, lights and external heat sources) played an important role in formation of the room airflow pattern. One interesting observation is that the temperature in the occupied zone is lower and a more stratified temperature field implies a more efficient heat removal by a stratified air supply device. The results revealed that the lowest temperature in the occupied zone was achieved for DSD, but with IJSD and WCJSD slightly warmer, while the system with a mixing supply device (MSD) showed a much higher temperature. The results confirm that air change effectiveness (ACE) for the DSD, WCJSD and IJSD is close to each other. However, MSD shows lower ACE in all the present papers than IJSD, WCJSD and DSD. Research question three showed that ventilation systems with stratified supply devices in almost all of the studied cases showed an acceptable level for predicted percentage dissatisfied (PPD), predicted mean vote (PMV) and percentage dissatisfied due to draft (DR). If comparing ventilation systems, using IJSD, WCJSD or DSD with MSD always showed thermal comfort better or at the same level. Människor spenderar en stor del av sin tid inomhus, exempelvis i sina bostäder och bilar, på tåg och på arbetet. Sveriges energibehov i den byggda miljön har en växande trend. Byggnadssektorn står för 40 % av det totala energibehovet och för 15 % av CO2 utsläppet och för cirka en tredjedel av energianvändningen i världen för att tillhandahålla en hälsosam och bra inomhusmiljö. För att skapa en bra inomhusmiljö har nya sätt att ventilera inomhusmiljön utvecklats under de senaste årtiondena. De olika principer som används för att ventilera en byggnad kan indelas i: kolvströmning, omblandande strömning och deplacerande strömning. De genererar rumsförhållanden som ger olika fördelning av hastighet, temperatur och föroreningar i det ventilerade utrymmet. Stratifierad ventilation är ett koncept som ofta ger ett bra utfall av både inomhusluftkvalitet och termisk komfort. Stratifierade system är effektiva för att minska korskontaminering, eftersom det nästan inte finns någon omblandning i rummet, temperaturen och föroreningskoncentration ökar linjärt från värmekällan med höjden i vistelsezonen. Det finns många olika ventilationsdon som använder den stratifierade principen, såsom deplacerande ventilationsdon (DSD), impinging jet-ventilationsdon (IJSD) och väggbaserad confluent jet-ventilationsdon (WCJSD). Huvudsyftet med denna avhandling är att analysera och jämföra olika tilluftsdon baserat på stratifierad princip i olika rumskonfigurationer med avseende på termiskt inomhusklimat, energieffektivitet och ventilationseffektivitet. Det yttersta målet är att bidra till ökad förståelse för hur ventilationssystem med olika stratifierade tilluftsdon fungerar. Två vetenskapliga metoder har huvudsakligen använts i denna avhandling: experimentella och numeriska analyser. För numeriska analyser har CFD (Computational Fluid Dynamics) använts. De simuleringsprogram som utnyttjats för detta ändamål är ANSYS och FIDAP. Experimenten har utförts med hjälp av termoelement, varmtråds- och varmsfärsteknik, mätutrustning för termisk komfort och mätutrustning för spårgas. Denna avhandling fokuserar framför allt på tre forskningsfrågor: interaktion mellan ett tilluftsflöde från ett deplacerande don och kallraset från ett fönster; strömningsbilden, energiprestandan och luftbyteseffektiviteten för olika tilluftsdon baserat på stratifierad ventilation; och termisk komfort för olika tilluftsdon baserade på stratifierad ventilation. Forskningsfråga ett visade att kombinationen av tilluftsflöde genom ett deplacerande don och fönster i kallt klimat har tydlig effekt på strömningsbilden för kallraset under fönstret. Olika tilluftsflöden har en effekt på både hastigheten och temperaturen i kallraset. I detta fall minskade hastigheten med ca 9,5% och temperaturen i kallraset minskade med 0,5°C när flödeshastigheten från tilluftsdonet ökade från 10 till 15 l/s. Forskningsfråga två visade att luftflödesmönstren mellan olika luftförsörjningssystem väsentligen var relaterade till egenskaper hos tilluftsdonen, såsom typ, konfiguration och position samt lufttillförselhastigheter och impulskraft. För WCJSD, IJSD och DSD spelade värmekällans placering, d.v.s. människor, datorer, belysning och externa värmekällor, en viktig roll vid utformningen av rummets luftflödesmönster. En intressant observation är att temperaturen i vistelsezonen är lägre och rummet har ett mer stratifierat temperaturfält, vilket innebär en effektivare ventilering av den zonen. Resultaten visade att den lägsta temperaturen i vistelsezonen uppnåddes för DSD medan IJSD och WCJSD visade en något högre temperatur, systemet med ett omblandande don (MSD) visade en påtagligt högre temperatur. Resultaten bekräftar också att luftförändringseffektiviteten (ACE) för DSD, WCJSD och IJSD ligger nära varandra. MSD visar dock i alla ingående artiklar lägre ACE än IJSD, WCJSD och DSD. Forskningsfråga tre visade att ventilationssystem med stratifierade tilluftsdon i nästan samtliga studerade fallen haren acceptabel nivå för predicted mean vote (PPD), predicted mean vote (PMV) och percentage dissatisfied due to draft (DR). Om man jämförde ventilationssystem IJSD, WCJSD eller DSD med MSD visade det sig alltid att den termiska komforten var bättre eller på samma nivå som för MSD.
Author: H.B. Awbi
Publisher: Elsevier
ISBN: 9780080430171
Category : Science
Languages : en
Pages : 746
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Book Description
The air distribution in occupied spaces is a major issue of public concern. It is widely recognized that the quality of air and the nature of airflow can affect the health of occupants and the energy consumed in buildings and transport vehicles. ROOMVENT is the principal international conference in the field of air distribution. It was first initiated in 1987 by SCANVAC, the Scandinavian Federation of Heating, Ventilating and Sanitary Engineering Associations in Denmark, Finland, Iceland, Norway and Sweden. The aim of the Conference is to bring together researchers from universities and research institutes, engineers from industry and government officials and policy makers, with the goal of experiencing the latest techniques for measuring and analyzing indoor air flow, the visualization of indoor air flow patterns, the evaluation of ventilation parameters and the most recent developments in computer simulation techniques of room airflow. It is hoped that the theme of ROOMVENT 2000 "Ventilation for Health and Sustainable Environment" will set the scene for room air distribution research and development for the new millennium.
Author: Vanita Kishore Negandhi
Publisher:
ISBN:
Category :
Languages : en
Pages :
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This dissertation presents the results of a study to determine the operational control, energy performance and comfort conditions associated with passive chilled beams for office buildings in a humid climate and to develop a method for the modeling of passive chilled beams with a ventilation system and underfloor air distribution (UFAD). For the analysis, a 606,900 ft2 commercial office building in ASHRAE climate zone 3A with passive chilled beams and a ventilation system with UFAD was selected as the case-study building. In the first step, measured data from the building was used to develop a calibrated whole-building energy analysis model in EnergyPlus 8.1. The energy model also implemented methods to model the controls found in a passive chilled beam system with underfloor air distribution. A simplified steady-state energy model was also developed for the validation of the EnergyPlus model and for energy use prediction. In the second step, two methods of optimization for the operational control strategies were tested: a simplified rule-based optimization and a model-based predictive control optimization. The influence of these two approaches to optimization on HVAC energy savings and thermal comfort were found to be within 2% of each other. Finally, summertime stratification measurements were taken in the offices and were combined with a CFD model of a single zone in Star CCM+ 9.04 to establish temperature and airflow profiles in the zones. These comfort studies were conducted for the cooling season only and showed that the thermostat setpoints are not fulfilled in the exterior zones in summer and chilled beam and ventilation system interact with each other and have an adverse effect on the overall system energy efficiency. The results of the research show that if properly controlled, a passive chilled beam system with a parallel ventilation system has the potential for HVAC savings of 14-24% over standard VAV systems in office buildings in humid climates. All of the HVAC energy savings come from fan and reheat energy. Energy savings are affected by latent loads and ventilation requirements in the zones and the potential for the use of an economizer. Indoor humidity levels are also higher with a passive chilled beam system than a standard VAV system. Independent control of the volume of air supplied by the ventilation system and the supply air temperature is necessary to achieve the predicted energy savings. Lastly, the summertime zone comfort studies reveal that the presence of the UFAD ventilation system hinders the natural downward plumes from the chilled beams and the presence of the chilled beam system inhibits stratification in the zones. Because of the lower ventilation flow rates associated with the chilled beams, there is significant increase in the temperatures in the supply plenums. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155687
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 284
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Author: Fergus Nicol
Publisher: Routledge
ISBN: 1136336478
Category : Technology & Engineering
Languages : en
Pages : 281
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Book Description
The fundamental function of buildings is to provide safe and healthy shelter. For the fortunate they also provide comfort and delight. In the twentieth century comfort became a 'product' produced by machines and run on cheap energy. In a world where fossil fuels are becoming ever scarcer and more expensive, and the climate more extreme, the challenge of designing comfortable buildings today requires a new approach. This timely book is the first in a trilogy from leaders in the field which will provide just that. It explains, in a clear and comprehensible manner, how we stay comfortable by using our bodies, minds, buildings and their systems to adapt to indoor and outdoor conditions which change with the weather and the climate. The book is in two sections. The first introduces the principles on which the theory of adaptive thermal comfort is based. The second explains how to use field studies to measure thermal comfort in practice and to analyze the data gathered. Architects have gradually passed responsibility for building performance to service engineers who are largely trained to see comfort as the ‘product’, designed using simplistic comfort models. The result has contributed to a shift to buildings that use ever more energy. A growing international consensus now calls for low-energy buildings. This means designers must first produce robust, passive structures that provide occupants with many opportunities to make changes to suit their environmental needs. Ventilation using free, natural energy should be preferred and mechanical conditioning only used when the climate demands it. This book outlines the theory of adaptive thermal comfort that is essential to understand and inform such building designs. This book should be required reading for all students, teachers and practitioners of architecture, building engineering and management – for all who have a role in producing, and occupying, twenty-first century adaptive, low-carbon, comfortable buildings.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 2
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This technical highlight describes NREL research to develop recommendations on HVAC system design and operating conditions to achieve optimal thermal comfort in high-performance homes. Researchers at the National Renewable Energy Laboratory (NREL) have developed recommendations to help residential heating, cooling, and ventilation (HVAC) designers select optimal supply inlet size and system operating conditions to maintain good thermal comfort in low heating and cooling load homes. This can be achieved by using high sidewall supply air jets to create proper combinations of air temperature and air motion in the occupied zone of the conditioned space. The design of air distribution systems for low-load homes is an integral part of residential system research and development in systems integration. As American homes become more energy efficient, space conditioning systems will be downsized. The downsizing will reach the point where the air flow volumes required to meet the remaining heating and cooling loads may be too small to maintain uniform room air mixing, which can affect thermal comfort. NREL researchers performed a detailed study evaluating the performance of high sidewall supply air jets over a wide range of parameters including supply air temperature, supply air velocity, and supply inlet size. They found that in heating mode, low and intermediate supply temperatures of 95 F (308 K) and 105 F (314 K) maintained acceptable comfort levels at lower fan powers than can be achieved at 120 F (322 K) supply temperatures. For the high supply temperature of 120 F (322 K), higher fan powers (supply velocities) were required to overcome buoyancy effects and reach a good mixing in the room. In cooling mode, a supply temperature of 55 F (286 K) provided acceptable comfort levels. A small supply inlet of 8-in. (0.2 m) x 1-in. (0.025 m) is recommended in both heating and cooling modes. Computational fluid dynamics was used to model heat transfer and airflow in the room. The technique consists of using the model output to determine how well the supply air mixes with the room air. Thermal comfort is evaluated by determining the Air Diffusion Performance Index (ADPI). The level of comfort is evaluated by monitoring air temperature and air velocity in more than 600,000 control volumes that make up the occupied zone of a single room. The room has an acceptable comfort level when more than 70% of the control volumes meet the comfort criteria on both air temperature and air velocity. Figure 1 illustrates the plots of acceptable draft temperature, which is between -3 ( -1.7) and 2 F (1.1 K) for two supply velocities of 394 fpm (2 m/s) (a) and 788 fpm (4 m/s) (b) when the room was supplied by 55 F (286 K) air. The plots show the distribution at selected cross-sections along the room. Colored regions on each cross-section are considered comfortable (blue regions are on the cold side and red regions are on the warm side). Regions of acceptable draft temperature are larger at low velocity and decrease as the velocity increases. As a result, the supply velocity of 394 fpm (2 m/s) provided higher comfort level than the supply velocity of 788 fpm (4 m/s). Work is in progress at NREL to extend this research to evaluate additional configurations and to integrate this system into a whole-house context.
Author: Hazim B. Awbi
Publisher: Psychology Press
ISBN: 0419217002
Category : Technology & Engineering
Languages : en
Pages : 459
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Book Description
This comprehensive account of the methods used for ventilating buildings and the type of systems currently in use for achieving the desired indoor environment will be of particular interest to graduate students, professionals and researchers.
