Microclimatic Conditions at the External Surface of Building Envelopes
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MICROCLIMATIC CONDITIONS DTU AT THE EXTERNAL SURFACE OF BUILDING ENVELOPES MIKKEL KRISTIAN KRAGIi $ RECEIVED FFr 2 5 1999 OSTI ajs'f?3‘.ara oJ- REPORT R-027 1998 ISSN 1396-4011 ISBN 87-7877-028-9 DEPARTMENT OF BUILDINGS AND ENERGY TECHNICAL UNIVERSITY OF DENMARK IBE DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. Errata MICROCLIMATIC CONDITIONS AT THE EXTERNAL SURFACE OF BUILDING ENVELOPES Mikkel Kristian Kragh. 1998. Report R-027. Department of Buildings and Energy. Technical University of Denmark N. Chapter Page Line Correction / Summary iv 21 ‘precipitation* should read ‘evaporation* ,v 2 2. Microclimate 24 Tiv formula: f,, given in [K] tdp should be given in [°C] 3 25 ‘Lund ’-formulae Reference: Htiglund, Ingemar. 1973. Metod fijr berakning af extreme yttemperaturer hos isolerade ytterkonstruktioner. Statens Institut for Byggnads- forskning. Rapport R6: 1973. Stockholm. Sweden. 4 30-32 precipitation/driving rain should be given in [mm/h] intensities given in ‘(mm)’ 5 5. Full-scale... 45 11 •Offset .„* should be disregarded 6 7. Long-wave... ‘Lund ’-formulae as above (3) 7 ‘Berdahl ’-formula should be disregarded - the application is dubious and the plot is erroneous. 8 8. Window ... 100 10 AT should read AT, 9 121 16-17 he should read 10 18 ‘convective film coeff. ’ should read ‘radiation and convection film coefficient* JJ 9. Meteorological ... 134 Table 9.2 Reference: Helbo Andersen, A. 1997. Slagrcgnspivirkning af klimaskaermskonstruktioner. Department of Buildings and Energy. Technical University of ■J Denmark. 12 Nomenclature 141 rh and rv given in [mm] should be given in [mm/h] , Errata v MICROCLIMATIC CONDITIONS AT THE EXTERNAL SURFACE OF BUILDING ENVELOPES PH.D. DISSERTATION BY MIKKEL KRISTIAN KRAGH Microclimatic Conditions at the External Surface of Building Envelopes Preface PREFACE The present dissertation concludes the Ph.D.-work entitled Microclimatic Conditions at the External Surface of Building Envelopes, carried out between August 1995 and August 1998. The project deals with the conversion from meteorological data to local conditions in a given position on a building envelope. The project is the first of its kind at the Department of Buildings and Energy, and represents as such a pilot study, hopefully continued by subsequent activities. The topic is both comprehensive and complex. The approach itself thus becomes an essential issue. Methodological problems are discussed, as the identification of the methodological problems is an absolute prerequisite to a scientific approach. The literature survey and the creation of a network in terms of contacts in external research environments have been time consuming. After the introductory phase, measurement activities were planned and financial support was applied for. As the literature study, the evaluation of potential areas of interest and the design and planning of measurements were the main aim, the measurement results obtained in the course of the project should be conceived as preliminary, and the activities should be continued after conclusion of the present project. As the subject is the climate around buildings, seasonal variations should be included in future studies. Acknowledgements Two private funds have granted the project with financial support for the realization of the measurement set-up, namely Fabrikant P.A. Fiskers Fond, and Martha og Paul Kerrn- Jespersens Fond. Without this support, the experimental part of the work would not have been possible. I wish to thank the members of the Microclimate Group, Fabien J.R. van Mook, Eindhoven University of Technology, and Anneli Hogberg, Chalmers University of Technology, for the fruitful exchange of ideas and results during the past two years. I also wish to thank my supervisor, Professor Svend Svendsen, Ph.D., who managed to find the time for a discussion, whenever it was needed. Thanks to my dear friend Niels Casper Andersen, a truly pleasant and educated interlocutor. Finally, I wish to express my heartfelt gratitude to my lovely wife Claudia for her admirable patience and support. Lyngby, August 1998 Mikkel Kristian Kragh i Microclimatic Conditions at the External Surface of Building Envelopes Structure of the dissertation The thesis is divided into five parts: PART I / Chapters 1, 2 and 3/BACKGROUND. The project is described, the motivation for the research and the microclimate is defined in relation to both building physics research and applications. The method is discussed in a philosophical perspective, as identifying methodological problems, and defining the method itself, are considered quintessential issues. PART II / Chapter 4/ANALYSIS. A fundamental introduction to the component microclimatic factors. Air temperature, air humidity, solar radiation and air velocity are briefly described for completeness, whilst driving rain and long-wave radiation are described in more detail. Convective heat transfer and surface coefficients are treated, although they are not microclimatic factors, merely resulting from combinations of such factors. They are included as they are important in relation to transfer of heat and moisture at the surface of the building envelope, and as they are related to the case studies of the project. PART III / Chapters 5, 6, 7, 8 and 9/METHOD. Selected subject are investigated in the form of case studies. Driving rain measurement is the main area of interest, including development of measurement equipment. Long-wave irradiation is measured and compared with empirical formulae from the literature. Window convection heat transfer is another main area of interest. Nocturnal convective heat transfer from a double pane glazing is studied and measurement principles are discussed. Finally, a compilation of meteorological data for hygrothermal simulations, including estimation of driving rain, is described. PART IV / Chapter 10/ FINDINGS. A brief summary of main conclusions in the dissertation. PART V / Appendices I, II and III/ APPENDICES. Auxiliary notes. System error estimation in relation to the window convection measurements, design notes on an apparatus for external convection measurement, formulae for conversion of relative humidity and dry- bulb temperature into dew point temperature. Keywords Building physics; Microclimate; Methodology; Driving rain; Driving min collector; Window convection heat transfer; Long-wave radiation; Climatic input for hygrothermal calculations; Recommendations for future studies. DEPARTMENT OF BUILDINGS AND ENERGY • TECHNICAL UNIVERSITY OF DENMARK • DK - 2800 LYNGBY Summary SUMMARY The present dissertation concludes the Ph.D.-project Microclimatic Conditions at the External Surface of Building Envelopes, carried out at the Department of Buildings and Energy between August 1995 and August 1998. The focus on the energy consumption perspectives has resulted in the developing of thermally well-insulating building components. Moisture in constructions may cause failure and unsatisfactory performance. Innovation of building components has lead to hitherto unknown problems caused by moisture in the constructions. One major objective of the current research is to establish models of the coupled heat and moisture transfer in order to develop construction types with satisfactory performance and long service life/durability. Such models depend on descriptions of the ambient climate, used as input for hygrothermal simulations. Hygrothermal simulations are usually based on use of the Design Reference Year, yielding one typical year of hourly weather data. However, whilst such data are recorded at a meteorological weather station, moisture critical situations may result from very local conditions, for instance in a particularly exposed position on a given building. In a building physical perspective, the (exterior) microclimate is defined as the conditions affecting transfer of heat and moisture in the immediate vicinity of the external surface of the building envelope. The microclimate results from a combination of meteorological factors and local characteristics. The microclimatic parameters are the following: • Temperature • Humidity • Long-wave radiation • Solar radiation corrected for shading objects • Driving rain • Air velocity The complex subject, and the project itself, are discussed in a philosophical context, and methodological problems are identified. In particular, the problems pertaining to the processes of preparation and interpretation are discussed - the preparation process being the delimitation of a well-defined object of a given investigation. The combination of complex climatic phenomena and the need for information, in terms of applicable guidelines, dictates a pragmatic approach, which, as a matter of fact, is also the case for engineering science in general. Adoption of parameter definitions, and assumptions regarding the relative significance of parameters, may to some extent predetermine the outcome of the research. Such assumptions and parameter definitions should thus be introduced consciously and with possible consequences in mind. It has been necessary to focus on selected topics owing to both time frame and financial limits. Analysis of the needs, in terms of input for hygrothermal calculations, has lead to the choice of three main areas of interest, namely: m Microclimatic Conditions at the External Surface of Building Envelopes • Driving rain • Long-wave radiation • Window convection heat transfer A full-scale microclimate