Research Project F W. Richter. Manual of thermal comfort of Summer cooling mode

Transcription

1 Research Project F 2071 W. Richter Manual of thermal comfort of Summer cooling mode Dortmund/Berlin/Dresden 2007

2 This publication is a summary of the final report of a project Development of a manual on how to exercise optimum influence on climatic conditions in working premises under summer conditions - Project F on behalf of the Federal Institute for Occupational Safety and Health. The responsibility for the contents of this publication lies with the author. Author: Prof. Dr.-Ing. habil. Wolfgang Richter In collaboration with: Dr.-Ing. Ralf Gritzki, Dipl.-Ing. Ingo Müller, Dr.-Ing. Alf Perschk, Dr.-Ing. Markus Rösler, Dr.-Ing. Klaus Windisch Technische Universität Dresden Institut für Thermodynamik und Technische Gebäudeausrüstung D Dresden Telephon: Telefax: Publisher: Federal Institute for Occupational Safety and Health Friedrich-Henkel-Weg 1-25, D Dortmund, Germany Telephone: Telefax: poststelle@baua.bund.de Internet: Berlin: Nöldnerstr , D Berlin, Germany Telephone: Telefax: Dresden: Proschhübelstr. 8, D Dresden, Germany Telephone: Telefax: All rights reserved, including photomechanical reproduction and the reprinting of extracts.

3 Manual of Thermal Comfort - Summary - Cooling systems for rooms are installed in buildings to secure thermal comfort in office buildings and comparable rooms, such as day and common rooms and lounges. It is therefore no wonder that there have long been considerations how to quantify this comfort criterion. For many years, the operative temperature (felt temperature) has been regarded a sufficient parameter which, however, only inadequately takes account of the influence of the indoor air flows. It was FANGER who made available numerous calculation equations that can be used for the assessment of thermal comfort. These equations have since then become part of the relevant standard DIN EN For the user, however, it is impossible to check the comfort conditions expected for the project he / she actually works on using the usual planning documents and design tools with the aim to make structural and HVAC modifications if necessary. In particular the assessment of the expected indoor air flows as the major influence on the comfort criterion 'draft risk' is thus limited to only few scientific institutions and plant manufacturers. This unsatisfactory situation has not really improved lately. To which extent does a larger wall-window area reduce thermal comfort? Is there any degree of freedom to the selection or arrangement of cooling components? These and further open questions need clear answers as thermal comfort is more and more understood as a decisive influencing factor of labour efficiency in particular during the summer. This manual is designed to give such answers on all aspects of thermal comfort for those interested in this subject, e.g., building owners, architects, HVAC engineers, structural physics specialists, hygienists, industrial safety engineers, landlords and tenants, but also for scientists with an interest in thermal comfort. They will find a variety of information about the decisive parameters:

4 2 - operative temperature (including 'boundary' velocities), - PMV (predicted mean vote), - PPD (predicted percentage of dissatisfied), - vertical air temperature profile, - radiant temperature asymmetry, - draft risk and also data on air velocity curves and surface temperatures. Important parameters are both civil engineering parameters, such as shading methods and wall-window ratio and also installation-related features like cooling systems or the arrangement and installation of components in the room. The intended easy utilisation of the results is clearly improved thanks to the thermal comfort classes A (high), B (intermediate) and C (moderate) in accordance with DIN EN The introduction of the so-called total thermal comfort is another step towards a user-friendly solution since it combines all global and local comfort criteria in an adequate manner (Table 1, Fig. 1). criterion category combination category PMV, PPD maximum radiant temperature asymmetry vertical air temperature gradient draft risk A B A C total thermal comfort C Table 1 Generation of the total thermal comfort using the categories of thermal environment A, B and C according to the standard DIN EN 7730 example The introductory part of the manual does not only give all necessary explanations on thermal comfort, it also provides all data about the calculation model, the choice of the most important boundary conditions and the processing of the results. As the manual is mainly designed for professionals with a practical interest in the subject, the presentation of the mathematical background is reduced to the minimum. Readers who are more interested in the mathematical foundations are referred to the references.

5 3 A number of conclusions can be drawn from the analysis of the results: Compared with heating in winter, summer cooling is generally accompanied by considerably larger variations in terms of thermal comfort. Accordingly, greater structural and installation-related efforts are necessary to attain sufficient thermal comfort in common rooms and lounges. It is also vital to take account of some global and local criteria (e.g., PMV and vertical air temperature gradient) which are more significant for summer cooling than for winter heating. Of the practically relevant influencing factors, such as thermal mass, shading, wall-window ratio and room cooling system which have been primarily examined, shading is by far the most decisive criterion from the structural point of view. Provided sufficient shading is realised, thermal mass and wall-window ratio are of subordinate importance. Similarly, the thermal insulation level and the outdoor climate have no noticeable effect. Principally, surface cooling produces clearly better thermal environmental conditions than air cooling systems. However, since the latter are related with the hygiene-related ventilation process, a comparison of both will not help achieve the objective. As regards surface cooling procedures, radiation-dominated plants have turned out to cause less trouble. The arrangement of the plant within the room is of subordinate importance, ceiling systems have minor benefits. In case of displacement ventilation, an effect of the air outlet arrangement, the air inlet temperature and also the volume flow (inlet velocity) can be shown. As practical experience shows, preference should be given to a greater air change rate instead of a larger temperature difference. Taking account of all criteria of thermal comfort in the form of a holistic assessment shows that the vertical arrangement of the air outlet has minor advantages. There are many types of air cooling procedures in the form of mixing ventilation systems. These types have been examined:

6 4 swirl ventilation (air outlet in the ceiling), induction device in the parapet wall, decentralised façade device (with incoming air function only) of which the latter eventually provides the more favourable thermal comfort values. However, a suitable selection, design or arrangement of alternative system components may qualify this statement.

7 vertical air temperature difference maximum radiation asymmetry 5 total thermal comfort draft risk PPD fig. 1 Example of generation of the total thermal comfort in a horizontal plane of 0,6 m height (surface cooling)

8 6 draft risk total thermal comfort without solar shading sun-blind overhang fig. 2 influence of solar shading - cooling ceiling; 30% glacing area; moderately heavy construction -

9 7 draft risk total thermal comfort air change rate n = 4 h -1 air change rate n = 6 h -1 air change rate n = 8 h -1 fig. 3 Influence of the air change rate - displacement ventilation; 30% glacing area; overhang -