1、System Performance Evaluationand Design Guidelines forDisplacement VentilationAbout the AuthorsQingyan (Yan) Chen is a professor of mechanical engineering at Ray W. HerrickLaboratories, Purdue University, West Lafayette, Indiana. He received his B.Sc. degreefrom Tsinghua University and M.Sc. and Ph.
2、D. degrees from Delft University of Tech-nology. He has published over 80 archival journal papers and more than 60 conferencepapers. Since 1995, he has been the principal investigator or co-principal investigatorof 30 sponsored research projects, including five from ASHRAE. He has been electedto the
3、 International Academy of Indoor Air Sciences. Currently, Prof. Chen serves asan associate editor for the International Journal of HVAC nor may any part of this book be reproduced,stored in a retrieval system, or transmitted in any way or by any meanselectronic,photocopying, recording, or otherwitho
4、ut permission in writing from ASHRAE.ASHRAE STAFFSPECIAL PUBLICATIONSMildred GeshwilerEditorErin HowardAssistant EditorChristina HelmsAssistant EditorMichshell PhillipsSecretaryPUBLISHING SERVICESBarry KurianManagerJayne JacksonProduction AssistantPUBLISHERW. Stephen ComstockvContentsPREFACE . . . .
5、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .viiACKNOWLEDGMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ixCHAPTER 1INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6、. .11.1 Displacement Ventilation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21.2 Special Features in U.S. Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . .31.3 Objective of This Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
7、CHAPTER 2LITERATURE REVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72.1 Temperature Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72.2 Flow Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .142.3 Co
8、ntaminant Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .212.4 Comfort Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .262.5 Energy and Cost Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .292.6 Des
9、ign Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33CHAPTER 3EXPERIMENTAL STUDY ANDVALIDATION OF CFD PROGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .353.1 Experimental Facility. . . . . . . . . . . . . . . . . . . . . . . . . . . .
10、 . . . . . . . . . .363.2 Test Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .393.3 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .423.4 Computational Fluid Dynamics Model . . . . . . . . . . . . . . . .
11、 . . . . . . . .423.5 Validation of CFD Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .453.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52CHAPTER 4MODELS FOR PREDICTION OF TEMPERATUREDIFFERENCE AND VENTILATION EFFECT
12、IVENESS . . . . . . . . . . . . . . . . .554.1 A Database of Displacement Ventilation. . . . . . . . . . . . . . . . . . . . . . .564.2 Model of the Air Temperature DifferenceBetween the Head and Foot Level . . . . . . . . . . . . . . . . . . . . . . . . . . . .704.3 Ventilation Effectiveness Model
13、. . . . . . . . . . . . . . . . . . . . . . . . . . . . .774.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79System Performance Evaluation and Design Guidelines for Displacement VentilationviCHAPTER 5PERFORMANCES EVALUATIONOF DISPLACEMENT VENT
14、ILATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815.1 Evaluation Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815.2 Performance Evaluation of Displacement Ventilation . . . . . . . . . . . . 845.3 Discussion . . . . . . . . . . . . . . .
15、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94CHAPTER 6ENERGY AND COST ANALYSIS . . . . . . . . . . . . . . . . . . . . . 956.1 Load Calculations. . . . . . . . . . . . . . . .
16、. . . . . . . . . . . . . . . . . . . . . . . . 956.2 Secondary Systems and Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1006.3 Energy Analysis for U.S. Conditions . . . . . . . . . . . . . . . . . . . . . . . . 1006.4 First Cost Analysis for U.S. Conditions. . . . . . . . . . .
17、. . . . . . . . . . . 1066.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107CHAPTER 7DESIGN GUIDELINES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111CHAPTER 8CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18、 . . . . 117NOMENCLATURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121INDEX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19、 . . . . . . . . . . . . . . . . . . . . . . . 127viiPrefaceThis book presents system performance evaluation and design guidelines fordisplacement ventilation. The authors first reviewed the literature concerning the performance of tradi-tional displacement ventilation. Since U.S. buildings have dif
20、ferent layouts andlarger internal heat gains than those studied in the literature, it was necessary todevelop design guidelines for displacement ventilation for U.S. buildings underdifferent climatic conditions.The design guidelines present two important models that were not available inthe literatu
21、re: a model to calculate the temperature difference between the head andfoot level of an occupant and a model to determine the ventilation effectiveness atthe breathing level. The investigation developed the models from the results of 56cases of displacement ventilation obtained by a computational f
22、luid dynamics(CFD) program. Those cases include a wide range of thermal and flow conditionssimilar to those found in U.S. offices, classrooms, and workshops. The CFDprogram was validated by six sets of detailed experimental data obtained from a full-scale environmental chamber simulating a small off
23、ice, a quarter of a large officewith partition, and a quarter of a classroom. The data include airflow patterns anddistribution of air velocity, temperature, contaminant concentration, and turbulence.The validation also used some data obtained from the literature. The CFD programwas also used to ass
24、ess the performance of displacement ventilation, such as airflowpattern and distributions of air temperature, percentage dissatisfied due to draft,predicted percentage dissatisfied, contaminant concentration, mean age of air, andventilation effectiveness. The investigation also conducted energy and
25、first costsanalysis.The results show that a displacement ventilation system can provide a thermallycomfortable indoor environment at a high cooling load through careful design. Theindoor air quality in a space with displacement ventilation is better if the contami-nant sources are associated with th
26、e heat sources. The displacement ventilationsystem can also save energy but requires a separate heating system if it is applied tobuilding perimeter zones. This book presents a ten-step design guideline to designthe displacement ventilation system for U.S. buildings.ixAcknowledgmentsThis book is bas
27、ed on the research performed for ASHRAE Research ProjectRP-949, “Performance Evaluation and Development for Design Guidelines forDisplacement Ventilation.” The research was sponsored by TC 5.3, Room AirDistribution, and TC 4.10, Indoor Environment Modeling. Throughout the research,the project monito
28、ring committee and the members of the two technical committeesmade a substantial contribution to the project, including numerous suggestions in theproject meetings, critical comments on the final report, and a site visit. The authorsare very grateful for their support and help. The authors would als
29、o like to thank theirformer research associates and students, Dr. Xiaoxiong (John) Yuan, Mr. ShipingHu, Ms. Yongqing Hu, and Prof. Xudong Yang, for their hard work on the project.Without their contributions, such a book would not exist. Last, but not least, theauthors are grateful to the ASHRAE Spec
30、ial Publications staff for their careful andbeautiful work on the book layout and edit.1CHAPTER 1IntroductionSince the energy crisis in the 1970s, the insulation of buildings has beenimproved in order to reduce heat loss in winter, heat gain in summer, and the infil-tration of outdoor air. As a cons
31、equence, the heat extracted from or supplied to aroom for maintaining a comfortable air temperature is reduced and the ventilationrate is also reduced by a corresponding amount, sometimes much more if the build-ing envelope is made tighter. However, such a reduction of air supply causes anincrease i
32、n the concentration of indoor pollutants and sometimes generates a non-uniform distribution of air temperature and contaminant concentration. Draft (ther-mal comfort problems) and “sick building” syndrome (indoor air quality problems)are very familiar ailments today that are the direct results of th
33、e poor distribution ofairflow, temperature, and contaminant concentrations. Solving these thermalcomfort and indoor air quality (IAQ) problems without consuming too much energyis a challenge for both ventilation engineers and architects.Currently, the United States consumes more than one-third of it
34、s energy inbuildings, and there is a possibility of saving up to 20% of this energy. Saving energymay result in the reduction of the fresh air supply. This may cause poorer IAQ. Sincepeople spend up to 90% of their time indoors, IAQ is increasingly recognized as anessential factor for the prevention
35、 of human diseases and the promotion of peoplescomfort and welfare. In the United States, about 800,000 to 1,200,000 commercialbuildings with 30 to 70 million people have problems related to IAQ (Woods 1989).The problems include eye, nose, and throat irritation, headache, recurrent fatigue,drowsines
36、s or dizziness, and reduced powers of concentration (Spengler 1995).Dissatisfaction with the working environment could result in reduced productivityand economic loss. A survey conducted in the New England area of 94 state govern-ment office buildings showed an average productivity loss of 3%, which
37、 is attributedto poor IAQ (Axelrad 1989). Fisk (2000) estimated that the economic impact relatedto respiratory illness, allergies and asthma, and sick building syndrome is $20 to$200 billion. Therefore, it is necessary to provide a good ventilation system that canprovide good IAQ and save energy.Sys
38、tem Performance Evaluation and Design Guidelines for Displacement Ventilation21.1 DISPLACEMENT VENTILATIONDisplacement ventilation has been used quite commonly in Scandinavia duringthe past twenty years. It was first applied to the welding industry in 1978 (Belin1978) and has since been increasingly
39、 used as a means of ventilation in industrialfacilities to provide good indoor air quality and save energy. More recently, its usehas been extended to ventilation in offices and other commercial spaces where, inaddition to air quality, comfort is an important consideration. In 1989 in Nordiccountrie
40、s, it was estimated that displacement ventilation accounted for a 50% marketshare in industrial applications and 25% in office applications (Svensson 1989).Displacement ventilation system can be divided into the following three types:Traditional displacement ventilation, as shown in Figure 1.1Displa
41、cement ventilation with a chilled ceiling panelDisplacement ventilation with a raised floorThis book focuses on the first type: traditional displacement ventilation. A typical displacement ventilation system for cooling, as shown in Figure 1.1,supplies conditioned air from a low sidewall diffuser. T
42、he supply air temperature isslightly lower than the desired room air temperature, and the supply air velocity islow (lower than 100 fpm or 0.5 m/s). Through the diffuser, the conditioned air isdirectly introduced to the occupied zone, where the occupants stay. Exhausts arelocated at or close to the
43、ceiling through which the warm room air is exhausted fromthe room. Because it is cooler than the room air, the supply air is spread over the floorand then rises as it is heated by the heat sources in the occupied zone. These heatFigure 1.1 Sketch of displacement ventilation.Introduction3sources (e.g
44、., persons and computers) create upward convective flows in the form ofthermal plumes. These plumes remove heat and contaminants that are less densethan air from the surrounding occupied zone. Traditionally, the amount of supply air in a displacement ventilation system hasbeen less than that of mixi
45、ng-type systems. This necessitates careful design of thesystem configuration and operation to adequately handle the space cooling loads.The supply temperature, velocity, and vertical temperature gradient in the occupiedzone are all very important comfort-related design parameters. Compliance with th
46、especification of ASHRAE Standard 55-1992 (ASHRAE 1992) for acceptable verti-cal temperature difference in the occupied zone places limitations on the magnitudeof supply-room temperature difference and/or space cooling loads for a given supplyairflow rate. This is especially important when the syste
47、m is applied to a U.S. build-ing in which the cooling load can be high and weather can be hot.Previous research (Svensson 1989; Sandberg and Blomqvist 1989; Wyon andSandberg 1990) has indicated that in office environments with normal room heightsof around 9 ft (2.7 m), displacement ventilation canno
48、t maintain acceptable comfortfor cooling loads above 8 to 10 Btu/(hft2) (25 to 30 W/m2) unless the air supplyvolume is increased or additional heat removal capacity is provided through the useof cooled ceiling panels. With higher ceiling heights, displacement ventilationsystems are capable of removi
49、ng larger heat loads. A stable, vertically stratified temperature field is essential for this type of systemto function properly. Numerous studies show that, when properly designed,displacement ventilation can take advantage of the naturally occurring thermal strat-ification in the room and, thus, can increase the ventilation efficiency.1.2 SPECIAL FEATURES IN U.S. BUILDINGSResearch on displacement ventilation has been mainly conducted in Scandina-vian countries. Recently, REHVA (2002) published a guidebook on designingdisplacement ventilation in non-industrial premises. Many U.S.
