Dedicated OA Systems

ASHRAE Transactions

Dedicated outdoor air systems (DOAS) are first defined. Then the single-space operating system, whose performance is presented here, is shown to conform to that definition. The controlled components are identified, along with the minimal instrumentation needed for control. Control of each component individually, and in the context of the whole, is presented. Supplemental controls to reduce terminal reheat energy consumption in multi-space applications are developed. Issues surrounding the use of CO 2-based demand-controlled ventilation, in light of ASHRAE Standard 62.1-2004 (former addendum 62n), are presented. Finally, experimental data are presented on the overall success of the DOAS design and control to provide air distribution and thermal comfort.

The control of air flow is important for several reasons: to control moisture damage, reduce energy losses, and to ensure occupant comfort and health. Airflow across the building enclosure is driven by wind pressures, stack effect, and mechanical air handling equipment like fans and furnaces. A continuous, strong, stiff, durable and air impermeable air barrier system is required between the exterior and conditions space to control airflow driven by these forces. Air barrier systems should be clearly shown and labelled on all drawings, with continuity demonstrated at all penetrations, transitions, and intersections. In addition, enclosure assemblies and buildings should be vertically and horizontally compartmentalized, may require secondary planes of airtightness (such as those provided by housewraps and sealed rigid sheathing) and may need appropriately air impermeable insulations or insulated sheathing.

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

2019

hygiene requirements Microclimate can be defined as a set of physical and chemical properties that we observe in a relatively small enclosed space, which has influence on living beings, for instance people, animals, etc. The main parameters are air purity and chemical composition, indoor temperature, relative humidity, velocity of air, and also temperature of the surrounding areas, lighting, noise level, furniture, color of walls and air ions (ASHRE, 2004; ASHRE, 2007). All components of the microclimate can significantly influence human mood, mental and physical performance, work efficiency and health condition (Skwarczyński & Dumała, 2002). It is worthy to note that comfort of a human being can be decreased by physical, chemical and biological pollutants. In case of the physical ones, the most important are noise and vibration, while in the group of biological pollutants we can distinguish for instance dust or bacteria. Most tests of Indoor Air Quality (IAQ) examine chemical components like nitrogen dioxide, sulphur dioxide, carbon monoxide, carbon dioxide or volatile organic compounds. The standards show indoor environment classes, although they differ in names:

2014

Publisher's PDF, also known as Version of record Link to publication from Aalborg University Citation for published version (APA): Iqbal, A., Nielsen, P. V., Gunner, A., & Afshari, A. (2014). Single-sided natural ventilation through a centre-pivot