Displacement Ventilation in Non-industrial Premises

Center for the Built Environment, 2006

Displacement ventilation has been successfully applied for more than twenty years in Europe and it represents an opportunity for China. Displacement ventilation (DV) is based on vertical stratification of temperature in the occupied zone of rooms. Buoyancy flows generated by heat sources govern the air distribution in rooms with DV. If properly designed DV has potential to provide higher ventilation effectiveness, i.e. better inhaled air quality for occupants and lower energy consumption than mixing ventilation. In order to avoid thermal discomfort due to draughts and vertical temperature difference, the temperature distribution should be carefully predicted in the design stage. The REHVA and ASHRAE methods to design displacement ventilation systems for thermal comfort are introduced in this paper and critically reviewed.

JAPAN ARCHITECTURAL REVIEW, 2021

This study aims to acquire an understanding of the fundamental feature of IJV and DV under heating operation. Full‐scale experiments were conducted under these two different systems and supply air conditions along with temperature distribution and ventilation effectiveness. A wall surface of the test room was cooled as a heating load, and heating elements simulating occupants were located as internal heat load and contaminant emission source. Three cases of supply temperature were tested and the flow rate was also varied correspondingly. The position of the supply terminal was also changed to see its effect on heating performance, that is, mounted on the interior/exterior wall. For DV, the temperature/contaminant distribution differed significantly depending on the supply conditions, while that of IJV remained almost the same as a perfect mixing condition. Generally, IJV can achieve better temperature distribution compared to DV; however, the ventilation effectiveness of DV was supe...

Renewable and Sustainable Energy Reviews, 1998

1990

hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers. The term airconditioning is generally understood to mean the heating, cooling and control of moisture in buildings. Consequently, this involves heating and cooling load calculations in addition to the design of plant components, ductwork and control systems. Ventilation, on the other hand, refers to the provision of sufficient quantities of outside air in the building for the occupants to breathe and to dilute the concentration of pollution generated by people, equipment and materials inside the building. This is necessary for both air-conditioned and non-air-conditioned buildings. The dilution of indoor contaminants is influenced by the quantity and quality of the outside air supplied to the building as well as the way this air is distributed around the space. The method of air distribution is also a vital part of any airconditioning system. In this book, the emphasis is on the last two themes, namely quantifying the outdoor air flow rate to a building and distributing this ventilation air around the space. During the last 15 years ventilation philosophy has been experiencing major changes. In the first part of this period, considerable efforts were made to understand the mechanisms of air infiltration in buildings in order to contol, and often to reduce, the fortuitous ventilation and conserve energy. In some cases, the reduction in air infiltration created problems associated with the air quality in the building and the generic term 'sick building syndrome' came into being. The second half of the same period experienced concerted efforts to understand the causes of sick buildings which resulted in the introduction of two new air quality units by Professor P.O.Fanger, namely the olf and the decipol, and a consensus for increased outdoor air flow rates. As a result of these changes, some ventilation standards, which initially recommended a reduction in outdoor air requirement for occupancy, had to increase these rates beyond those recommended prior to this period. Reflecting the current attitude, the new ASHRAE Standard 62-1989 has increased the minimum outdoor air per person from 2.5 l s-1 to 7.5 l s-1, i.e. a threefold increase. This book has been designed to complement rather than replicate the HVAC handbooks such as those by ASHRAE and CIBSE. Where appropriate the theory of a design problem is given to broaden the readers' horizon of the subject. Recent developments in ventilation requirements, thermal comfort, indoor air quality and room air distribution are also included. The text is intended for the practitioner in the building services industry, the architect, the postgraduate student taking courses or researching in HVAC or general building services and the undergraduate studying building services as a major subject. The book assumes that readers are familiar with the basic principles of fluid flow and heat transfer and knowledgeable with regard to the thermal characteristics of building fabric. However, Chapter 7 requires more advanced knowledge of partial differential equations which describe the turbulent flow and heat transfer processes of fluids. Chapter 1 presents the theory and practice of thermal comfort and indoor air quality (IAQ) in some detail, including recent advances in these areas based largely on the work of Fanger and his associates. Chapters 2 and 3 describe the procedures used in determining ventilation rate requirements for different occupancy and the methods of determining air infiltration rates and the design of passive and smoke ventilation techniques. Chapters 4 and 5 outline the theory of different types of air jets, including the influence of buoyancy, Coanda force and obstructions, and the aerodynamic characteristics of various air terminal devices used in practice. Chapter 6 presents, in some detail, the theory of physical modelling as applied to room air movement and discusses the influence of various fluid and heat flow parameters on the modelling process. This chapter also contains case studies involving reduced-scale and prototype measurements. Design procedures for different room air distribution methods are also presented here. Chapter 7 is devoted to the theory of computational fluid dynamics (CFD) as applied to ventilation and room air movement and presents the results of recent publications to illustrate the state of the art in this rapidly expanding field of ventilation research. Finally, Chapter 8 deals with the principles of measuring air temperature, radiant temperature, humidity, pressure, air velocity, air flow rate, thermal comfort, indoor air contamination and air flow visualization. This book provides the reader with recent developments in the subject which are largely missing from other titles currently available. The ultimate aim is, of course, better design of ventilation systems to reduce the frequency of public complaints about HVAC systems which have increased in recent years. Finally, with the subject of intelligent buildings of the future frequently being mentioned, it is hoped that this book will provide the designer of ventilation systems for these buildings with some of the necessary information. H.B.Awbi 1.3.5 Field studies The temperature indices described previously have largely been derived from data obtained in environmental chambers and laboratories where consistent control of the environmental parameters is maintained during the experiments. Although such tests provide accurate evaluation of the influence of each parameter or a group of parameters on the thermal sensation of people, the subjects involved are not in their familiar surroundings nor are they engaged in their usual work activities throughout the test periods. The subjects in the laboratory tests may therefore lack the opportunity to adjust to the thermal environment as people do in normal life. This anomaly can be overcome by conducting field studies where people's thermal response is investigated in their usual work environments. A number of field investigations are reported in the literature [15-18]. Humphreys [15] analysed the results of more than 30 field studies of thermal comfort conducted over a period of 40 years in about 12 countries of different climatic conditions. All the investigations were conducted indoors, the majority of which were in offices, i.e. light activity. The mean temperatures for these studies range from 17 °C for English homes in winter to 37 °C for offices in summer in Iraq. In the latter study, the temperature was adjusted to allow for the abnormally high air velocities to 34 °C. The temperatures recorded in these investigations were air and/or globe temperatures which differed little in most cases. From the temperature measurements and the survey results it was possible to establish the neutral temperature for the subjects involved. This is the temperature at which the respondent to the survey is thermally neutral. Allowing for the high air movement in a hot environment, Humphreys obtained a range of neutral temperatures from 17 to 30 °C. Other, but less wide-ranging, surveys in offices were carried out by Auliciems [16] in Australia, Fishman and Pimbert [17] in England and Schiller et al. [18] in USA. These studies produced neutral temperatures of 20.5 to 23.1 °C; 22.0 °C; 22.0 °C (winter) and 22.6 °C (summer) respectively. In the study by Schiller et al. the winter neutral temperature compares well with the comfort temperature recommended by ASHRAE Standard 55-1981 [9], however the neutral temperature in the summer was lower than that recommended by the Standard (24.5 °C). This indicates that people tend to prefer cooler conditions in the summer than those suggested by the Standard, which is largely based on laboratory test data. The results from these field studies suggest that people tend to adjust to their environment. However, one must remember that field data normally have lower degrees of correlation than laboratory-based measurements and further research is needed in assessing thermal acceptability in normal daily environments. 45. ASHRAE Standard 62-1989 (1989) Ventilation for acceptable indoor air quality, American Society of Heating Refrigeration and AirConditioning Engineers, Atlanta, GA. 46. BS 5925 (1980) Code of practice for design of buildings: Ventilation principles and designing for natural ventilation, British Standard Institution, London. Chapter two Ventilation requirements 2.1 Introduction Recently, ventilation has assumed a new dimension in the building design process as a result of the much publicized 'sick building syndrome'. This is fundamentally a complaint about the indoor air quality of a building which is more common in air-conditioned buildings than in naturally ventilated buildings [1]. Building sickness comprises the sensation of stuffy, stale and unacceptable indoor air, irritation of mucous membranes, headache, lethargy and so forth. These problems have recently intensified as a result of a global reduction in the supply rate of outdoor air to buildings

Indoor Air, 2014

In the preface to this book the author, Hazim Awbi, states that, during the last three decades, ventilation philosophy has been experiencing major changes. In the first decade of this period, considerable efforts were made towards understanding the mechanisms of air infiltration in buildings in order to reduce fortuitous ventilation and conserve energy. In some cases, the reduction in air infiltration created problems associated with the air quality in buildings and the generic term 'sick building syndrome' came into being. The second decade experienced concerted efforts to understand the causes of sick buildings, which resulted in the introduction of new ventilation concepts, such as the age of air, new air quality units, and a consensus for increased outdoor air flow rates. In the third decade, the emphasis on reducing energy consumption and awareness of environmental concerns has focused the minds of researchers and designers alike on the potential of natural ventilation and user control of the local environment. As a result of these changes, new ventilation standards and guidelines have been written to reflect the importance of ventilation on the quality of the indoor environment.

The present study presents the experimental study of performance of the displacement ventilation . The experimental study included the effect of different internal loads of (1600,1300and 1000)W , different supplied air temperatures of ( 18,20,22and 24)?C and different supplied air velocities (0.75,1,1.25 and 1.45)m/s on the performance of displacement ventilation . The experimental results show that the cooling capacity of air increases as the temperature of supplied air decreases. At a increases in temperature of supplied air by (33.33)%,the cooling capacity of air decreases by (23.52, 24.05 and 20.63)% for internal load of (1600,1300 and 1000 )W respectively .While as supplied air velocity increases ,the cooling capacity of air increases .At supplied air increases by (93.33)% ,the cooling capacity increase by (33.61, 39.23 and 36.8 )% for internal load of (1600, 1300 and 1000)W respectively.

Displacement ventilation (DV) systems are characterized by thermal stratification that cannot be adequately modeled using the fully mixed room air approach that is common in overhead air conditioning system design. This paper presents a simplified approach for DV that models the room thermal stratification using three air temperature nodes: lower layer (floor level), occupied zone and upper layer. The proposed approach is a development of one of the two models currently available in the thermal simulation tool EnergyPlus. A methodology for locating the neutral height in temperature profiles was developed. This methodology was used to verify the applicability of Morton et al. (1956) plume flow equation to predict the neutral level in DV rooms. The proposed model was successfully validated using nine different scenarios from three independent experimental studies. The model provides significantly improved precision when compared to existing DV nodal models, in particular in the floor level and occupied zone temperatures.

Building and Environment, 2001

This paper is concerned with the di erence in the air quality that is perceived by the occupants (breathing zone) and that existing in the occupied zone as a whole. An environmental chamber with displacement ventilation system has been used to carry out the measurements with the presence of a heated mannequin and other heat sources. Measurements of the age of air distribution, the air exchange index and the ventilation e ectiveness were carried out at di erent points in the chamber for di erent room thermal loads. CFD simulations were also carried out for the purpose of ow visualisation as well as the calculation of air velocity, temperature and age of air distribution. In addition, CFD simulations were carried out to study the e ect of changing the air ow rate to the chamber and the position of air inlet to extend the range of parameters. The results from the CFD simulations were compared with those from measurements and good agreement was obtained in most cases.

Measurements and CFD simulations from four systems are compared using the air change index and a new Ventilation Parameter (VP). VP combined with thermal comfort and indoor air quality indices gives a good index for comparison of four systems. Impinging Jet is capable of achieving better air distribution in the space than the other systems (mixing, wall displacement and floor displacement) particularly at higher heat loads.

2005

International Journal of Ventilation, 2003

Energy and Buildings, 2010

Design guidelines envisage that floor heating can be used together with displacement ventilation (DV), provided that the supply air is not overly heated before it can reach heat and contaminant sources. If this is not controlled a mixing flow pattern could occur in the room. The use of floor cooling with DV is also considered possible, although draught risk at ankle level and vertical air temperature differences must be controlled carefully, because they could increase.