Natural Ventilation in Buildings Architectural concepts, consequences and possibilities by Tommy Kleiven Thesis submitted in partial fulfilment of the requirements for the degree of Doktor Ingeniør at Norwegian University of Science and Technology Faculty of Architecture and Fine Art Department of Architectural Design, History and Technology March 2003 URN:NBN:no-7242 URN:NBN:no-7242 Preface Natural ventilation in buildings relies on wind and thermal buoyancy as driving forces. Humankind has used these driving forces throughout history to create the desired thermal environment and to transport away undesired contaminants. From the first primitive living quarters with the fireplace in the centre of a tent or a cabin, the technique we take advantage of to control and adjust our indoor climate has grown ever more sophisticated. This technique has in the 20th century been dominated by mechanical ventilation and air conditioning. These technologies have developed into systems of great complexity with an increasing number of components, need for space, and use of energy. Despite this, many of the mechanical systems do not manage to deliver the desired indoor climate. Because of this contradiction, the focus has again been put on simpler, more robust and less energy consuming solutions. The driving pressures derived from wind and thermal buoyancy are low compared to those produced by fans in mechanical ventilation systems. It is therefore necessary to minimise the resistance in the airflow path through the building. Thus, the building itself, with its envelope, rooms, corridors and stairways, rather than the ducts familiar from mechanical ventilation systems, is used as air path. A natural ventilation concept is therefore highly integrated in the building body and will consequently have influence on building design and architecture. Le Corbusier’s perhaps most famous dictum was “a house is a machine for living in.” In the context of natural ventilation it can be said that the building in itself is a machine, and not a structure to put a machine into. This work examines the relationship between building design and natural ventilation. The work tries in the first instance to seek out the architectural consequences of natural ventilation, and in the next instance to find out to what extent the natural airflow has a potential of being a design criterion, a contributing parameter in the design of buildings. The primary goal of this study is to offer a better understanding of the architectural presuppositions for utilisation of natural ventilation, and from that suggest some architectural possibilities associated with the utilisation of natural driving forces. The target group of this thesis is primarily architects in general and researchers within the field, but also other actors in the building industry, e.g. consultants, contractors and building owners, may find this study of interest. URN:NBN:no-7242 URN:NBN:no-7242 Contents Abstract 6 1 Introduction 7 1.1 Research field 8 1.2 Research questions 13 1.3 Focus 15 1.4 Research approach 16 1.5 Outline of the dissertation 22 2 Principles and elements of natural ventilation 27 2.1 The purpose of ventilation 30 2.2 Natural driving forces 36 2.3 Natural ventilation principles 41 2.4 Local and central supply and exhaust paths 44 2.5 Combination of natural and mechanical ventilation 46 2.6 Characteristic elements of natural ventilation 52 3 Case studies and architectural aspects 71 3.1 Classification of natural ventilation concepts 72 3.2 Selection of case study buildings 76 3.3 Checklist for architectural aspects 79 4 Natural ventilation in a high-rise building 83 4.1 Description of the GSW case study building 85 4.2 Architectural consequences of natural ventilation in GSW 98 4.3 Experiences of the design team 117 4.4 Summary and conclusions 121 5 Natural ventilation in a medium-rise building 127 5.1 Description of the B&O case study building 128 5.2 Architectural consequences of natural ventilation in B&O 141 5.3 Experiences of the design team 158 5.4 Summary and conclusions 160 6 Natural ventilation in a low-rise building 167 6.1 Description of the Mediå School case study building 168 6.2 Architectural consequences of natural ventilation in Mediå School 177 6.3 Experiences of the design team 190 6.4 Summary and conclusions 192 7 Architectural possibilities of natural ventilation 197 7.1 Possibilities related to the façade 200 7.2 Possibilities related to the roof 216 7.3 Possibilities related to the plan and the section 224 7.4 Possibilities related to the interior spaces 235 8 Conclusions and reflections 257 8.1 Findings regarding the architectural consequences of natural ventilation 258 8.2 Findings regarding the architectural possibilities of natural ventilation 265 8.3 Design team experiences and implications for future designs 267 8.4 Further research and development 270 Literature 271 Appendix: Sub-case buildings 281 Acknowledgements 304 URN:NBN:no-7242 Abstract This thesis, “Natural Ventilation in Buildings -Architectural concepts, consequences and possibilities”, is the result of a PhD study financed by Hydro Aluminium/Wicona, The Research Council of Norway and the Norwegian University of Science and Technology (NTNU). The work was carried out at the Department of Architectural Design, History and Technology, Faculty of Architecture and Fine Art at NTNU in the period January 2000 to March 2003. The study has been conducted in close collaboration with fellow researchers Bjørn J. Wachenfeldt and Tor Arvid Vik. Chapter 2 “Principles and elements of natural ventilation” is in its entirety written by the three of us together. The main objectives of this work have been to identify and investigate the architectural consequences and possibilities of natural ventilation in office and school buildings in Northern Europe. Case studies and interviews with architects and HVAC consultants have been the most central “research instruments” in achieving this. Three buildings have been studied in detail. These are the GSW Headquarters in Germany, the B&O Headquarters in Denmark, and the Mediå Primary School in Norway. In addition, a larger set of buildings has been used to substantiate the findings. The most important findings of this work are that: utilisation of natural ventilation in buildings has architectural consequences as well as possibilities. natural ventilation primarily affects the facades, the roof/silhouette and the layout and organisation of the interior spaces. the ventilation principle applied (single-sided, cross- or stack ventilation) together with the nature of the supply and extract paths, i.e. whether they are local or central, are of key importance for the architectural consequences and possibilities. designing a naturally ventilated building is more difficult than designing a similar but mechanically ventilated building. An interdisciplinary approach from the initial stages of design is mandatory for achieving successful natural ventilation concepts. URN:NBN:no-7242 1 Introduction This work examines the relationship between building design and the utilisation of natural ventilation in high-rise, medium-rise and low-rise buildings. By studying and comparing these three generic building types, the study explores how the architecture of naturally ventilated buildings of varying height is affected. This should make it possible to find out if there are different sets of “rules” for utilisation of natural ventilation for the three generic building types, and then implicitly if there are differing architectural consequences and possibilities for the three types. The basic idea is that natural ventilation is so integrated with the building, in fact is a part of the building, that it will have significant consequences for the building design and the architectural expression both in the exterior and in the interior. Furthermore, the utilisation and characteristics of the two natural driving forces associated with natural ventilation, thermal buoyancy and wind, are influenced by the height of the building. As a consequence, the naturally induced airflow is an important parameter among all the other parameters contributing to the shaping of a building. The natural airflow, described by the laws of physics, can thus be regarded as an important design criterion in the design of naturally ventilated buildings, constituting a design instrument for the architect and the consultants. This chapter describes why and how this study has been conducted. The chapter starts by describing the research field that has been addressed, in section 1.1. From this description a set of research questions are formulated in section 1.2. The focus of the research is described in section 1.3. A description of the research strategy, i.e. an explanation of how the research questions will be answered, is presented in section 1.4. The chapter ends with an outline of the dissertation in section 1.5. URN:NBN:no-7242 Chapter 1. Introduction 1.1 Research field Why natural ventilation? Or, the heading could rather have been formulated: why natural ventilation again? Natural ventilation, relying on wind and thermal buoyancy as driving forces, is surely not a new phenomenon or invention. Utilisation of the natural driving forces for the purpose of ventilation has for several millennia provided the desired thermal comfort and air quality for both man and animals1. I thought I heard Buddy Bolden say, Open up that window, let the foul air get away! Open up that window, let the foul air out! That’s what I heard him shout. Traditional (Banham, 1969). Figure 1.1 Wind and thermal buoyancy, here illustrated with the wind blowing in a tree (left) and a glider ascending attributable to thermal buoyancy (right), are the two natural “engines” that can be utilised to drive air in, through and out of buildings. The use of a mechanical driving force, i.e. fans, to drive the ventilation through a network of ducts has however dominated over natural ventilation in the twentieth century.