REFURBISHMENT OF AIR-CONDITIONED BUILDINGS FOR NATURAL VENTILATION

Transcription

1 Technical Note TN 8/98 REFURBISHMENT OF AIR-CONDITIONED BUILDINGS FOR NATURAL VENTILATION Chris Kendrick Andrew Martin William Booth B

2 Technical Note TN 8/98 REFURBISHMENT OF AIR-CONDITIONED BUILDINGS FOR NATURAL VENTILATION - rest of title Chris Kendrick Andrew Martin William Booth The Building Services Research and Information Association Old Bracknell Lane West, Bracknell, Berkshire RG12 7AH Tel: + 44 (0) Fax: + 44 (0) bsria@bsria.co.uk B

3 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without prior written permission of the publishers. ISBN Printed by Oakdale Printing Co. BSRIA August 1998

4 SUMMARY SUMMARY It has been demonstrated in a number of case study buildings that it is possible to maintain a comfortable environment when refurbishing without resorting to full mechanical ventilation or cooling. The benefits of natural ventilation include lower running and maintenance costs, possibly less capital outlay, increased useable/lettable area due to reduced number or size of plant rooms, and potential for increased occupant satisfaction by local control over internal environmental conditions. The use of a naturally ventilated solution rather than an airconditioned one can certainly result in a more robust building, less susceptible to deficiencies in maintenance. The use of passive strategies applied to a refurbished building requires careful design if the building is to be successful. Selection of the optimum passive measures will enable comfortable indoor conditions to be maintained or enhanced. This guidance for refurbishing air-conditioned buildings to utilise natural ventilation is aimed at buildings where consideration is being given to the removal of mechanical ventilation and /or mechanical cooling plant. The guidance is also particularly appropriate where conventional naturally ventilated buildings are to be upgraded to incorporate passive cooling techniques. The use of mechanical ventilation as part of a mixed mode solution is not precluded however, as it is the only viable option in some cases. BSRIA TN 8/98 Refurbishment for Natural Ventilation

5 ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS BSRIA would like to thank the following sponsors for their contribution to the research project: Department of the Environment, Transport and the Regions British Broadcasting Corporation EA Technology Health and Safety Executive London Electricity Plc Metropolitan Police Service Midlands Electricity Plc. Acknowledgement is also given to the following companies who provided assistance: Acoustic Consultants Atelier Ten Battle McCarthy Bickerdike Allen Partners Ben Morris (Architect) Bennetts Associates British Cement Association Feildon Clegg Architects Gardiner and Theobald Leicester City Council Max Fordham and Partners McMahon and Curtis The MDA Group UK Nick McMahon Ltd Northcroft The Open University Oxford County Council Price and Myers Reinforced Concrete Council RMJM Rybka Battle The Steel Construction Institute WS Atkins. Whilst every opportunity has been taken to incorporate the views of the sponsors, final editorial control of this document rests with BSRIA. BSRIA TN 8/98 Refurbishment for Natural Ventilation

6 CONTENTS CONTENTS 1 INTRODUCTION INITIAL ASSESSMENT Reasons for refurbishment for natural ventilation REDUCING HEAT GAINS General Heat gains from people Heat gains from electrical equipment Heat gains from lighting Artificial lighting Daylighting Solar control NOISE ATTENUATION The noise problem Estimation of traffic noise Noise reduction VENTILATION DESIGN Design approaches Design for cross ventilation Design for single-sided ventilation Design for passive stack ventilation Winter ventilation and air tightness Control of air movement Choice of windows for natural ventilation NATURAL VENTILATION STRATEGIES FOR DEEPER PLAN SPACES General Use of stairwells Stairwell smoke control Solar chimneys and double facades The addition of atria and ventilation shafts Atrium canopies Atrium smoke control Use of redundant chimneys Proprietary stack system Designing shaft terminations General Design solutions USING THE THERMAL CAPACITY OF THE BUILDING FABRIC Exposing the thermal capacity Thermal mass in the structure Practical measures General Routing of services Ceiling finish Acoustic environment Night cooling MIXED MODE OR HYBRID BUILDINGS Types of mixed mode BSRIA TN 8/98 Refurbishment for Natural Ventilation

7 CONTENTS 8.2 Reasons for mixed mode Design solutions Control OPERATIONAL GUIDANCE Commissioning Testing and inspection - handover procedures Staff training Operational problems CASE STUDIES Case study A Background Refurbishment design Case study B Background Refurbishment design Assessment of occupant satisfaction and environmentalconditions at Office A and Office B General assessment procedure Environmental data Questionnaires Building sickness data Environmental perception Effects of refurbishment Usage of opening windows Conclusions REFERENCES Refurbishment for Natural Ventilation BSRIA TN 8/98

8 LIST OF TABLES LIST OF TABLES Table 1 Natural ventilation characteristics of different building types... 3 Table 2 Feasibility study considerations... 5 Table 3 Aid to assessing building suitability for natural ventilation (having assessed heat gains)... 6 Table 4 Aid to assessing levels of refurbishment required for different building suitability scores and heat gains... 6 Table 5 Cost and heat gains associated with different levels of refurbishment... 7 Table 6 Occupancy heat gains... 9 Table 7 Office equipment power loads Table 8 Lighting power loads (400 lux on working plane) Table 9 Lighting control costs Table 10 Solar control glass: with 12 mm air space and 6 mm clear float inner pane Table 11 Budget costs for a range of solar shading options Table 12 Comparison of solar control methods Table 13 Recommended indoor noise criteria Table 14 Properties of various windows and noise reducing techniques Table 15 Benefits/disadvantages of natural ventilation Table 16 Advantages and disadvantages of different window types Table 17 Budget costs for two options for building refenestration Table 18 Advantages and disadvantages of solar chimneys and double facades Table 19 Advantages and disadvantages of different shaft termination designs (see Figure 12) Table 20 Building environmental data after refurbishment Table 21 External maximum and minimum temperatures during building occupied hours over the test period Table 22 Number of days for CO 2 peaks after refurbishment Table 23 Descriptors for BSI(5) categories Table 24 Environmental descriptions and acceptability after refurbishment Table 25 Levels of discomfort before and after refurbishment Table 26 Change in regularity of discomfort between before and after refurbishment BSRIA TN 8/98 Refurbishment for Natural Ventilation

9 LIST OF FIGURES LIST OF FIGURES Figure 1 Progressive stages of introducing natural ventilation... 8 Figure 2 Hours over stated resultant temperatures in the occupied period for different shading/ventilation options for Park House Figure 3 Effect on resultant temperature of different options compared with reference case Figure 4 Kerbside road traffic noise Figure 5 Road traffic noise decay with distance Figure 6 Wind driven ventilation - cross ventilation Figure 7 Wind driven ventilation - single sided ventilation Figure 8 Temperature driven ventilation in a stack Figure 9 Computer model showing variation between stack and wind driven ventilation rates Figure 10 Relative air flow through hinged windows of different aspect ratios (L/H) compared with an open aperture of the same area Figure 11 Typical arrangements of concrete slabs [30 ] Figure 12 Shaft terminations on new naturally ventilated buildings Figure 13 Office A and B populations, target and responding groups Figure 14 Building sickness score by building and gender after refurbishment Figure 15 Percentage of group suffering numbers of symptoms after refurbishment Figure 16 Reasons for opening windows after refurbishment Figure 17 Reasons for not opening windows after refurbishment Refurbishment for Natural Ventilation BSRIA TN 8/9

10 INTRODUCTION SECTION 1 1 INTRODUCTION Commercial refurbishment is becoming an increasingly viable alternative to new-build, with many 1960s and 1970s buildings now at the end of their leases and ready for renovation. Refurbishment is undertaken for a number of reasons ranging from a need to improve the poor condition of the fabric to a need to cater for heat gains from an increasing amount of electrical equipment or increased occupant numbers. Advantages of refurbishment over new-build include potentially lower capital cost, shorter completion times and avoidance of planning constraints, which can be imposed on a new-build. This document is intended as a design guide and source book to provide an overview of the various techniques available when refurbishing buildings. The guidance is equally applicable when the removal of mechanical ventilation and cooling is being considered or when existing naturally ventilated buildings require enhancement. The guidance is particularly useful where measures are being considered to ameliorate overheating in naturally ventilated buildings. Case studies in this document demonstrate that it is possible to provide a comfortable environment through appropriate refurbishment without resorting to full mechanical ventilation or cooling. These projects also show that high-class accommodation can be achieved in such buildings despite their inherent constraints, and that the viability of natural ventilation is improving as advances in the efficiency of equipment and lighting means that they contribute less heat to their surroundings, thus reducing the need for mechanical services to keep conditions comfortable. The use of new technologies such as carbon fibres and adhesives to reinforce structures is also increasing possibilities for refurbishment of older commercial building stock. Natural ventilation is suitable for most offices not severely affected by noise or pollution. The benefits of natural ventilation can include lower running and maintenance costs, possibly less capital outlay, increased useable/lettable area with fewer plant rooms, and the potential for increased occupant satisfaction when given local control over internal environmental conditions. The link between air-conditioning and sick building syndrome is not proven, but a natural ventilation solution can certainly result in a more robust system, less susceptible to deficiencies in maintenance. The breadth of the subject area demands that reference be made to other texts where individual topics are covered in more detail, whilst the diversity of potential buildings precludes a detailed step-by-step approach. Instead, a methodology is proposed, along with potential solutions and case studies which might be used to add value to the project under consideration. BSRIA TN 8/98 Refurbishment for Natural Ventilation 1