DESIGN MASTERCLASS 8 HEAT LOSS
Diurnal variations in external temperature are attenuated by building envelopes to the extent that they contain thermal mass to partially absorb the energy flow. This results in a dynamic insulation property known as decrement
performance, we will also need to account for it in the heating condition. Consider a traditional brick wall with insulated cavity. The decrement factor from exterior to interior is 0.26, with a decrement delay of about 10 hours. The decrement factor is applied to the steady state U-value heat transfer. Thus the heat absorbed at the exterior during the day is only transmitted to the interior at a fraction of the intensity during the night. Conversely, during the daytime, the interior experiences passive cooling as a result of the heat loss from
the previous night. Consider now that the construction is symmetrical inside to outside as it is outside to inside. The same decrement factor and delay must therefore also apply to heat flowing outwards in the winter. So, we must now consider the insulation of conventional masonry construction as being dynamic over the diurnal cycle. The same applies, to a greater or lesser extent, to any form of envelope construction, and this must surely be an essential part of our understanding of building envelopes. The building envelope is the primary means of creating a comfortable and stable internal environment yet, outside academia, it is one of the least rigorously analysed aspects of the building services design. As we move forward we will need a concerted effort to refine our understanding of building envelope performance and to ensure that building services engineers are in a position to lead on this fundamental aspect of carbon performance. © Doug King
l Doug King is principal of consulting engineers King Shaw Associates and visiting professor of building physics at Bath University.
Future features in CIBSE Journal
PASSIONATE ABOUT THE BUILT ENVIRONMENT?
We are … and we have been for 90 years. Our industry expertise allows us to provide specialist courses for property and construction professionals, by supported distance learning.
We offer diploma, undergraduate and postgraduate courses. Degree courses are awarded by the University of Reading and accredited by RICS, CIOB and other professional bodies. Courses include:
• BSc in Building Services Quantity Surveying • BSc in Building Surveying • BSc in Construction Management • BSc in Estate Management • BSc in Property Management • BSc in Quantity Surveying
To further your career call 0800 019 9697 (quoting ref: CJ11), email
coursescem.ac.uk or visit our website.
For advertising opportunities contact:
Jim Folley – 020 7324 2786 or email
jim.folley@
redactive.co.uk
Mark Palmer – 020 7324 2785 or email
mark.palmer@
redactive.co.uk
40 40
CIBSE Journal August 2011 CIBSE Journal August 2011
www.cibsejournal.com www.cibsejournal.com
September 2011 Air conditioning, air movement & ventilation
October 2011 Industrial & commercial heating Pipework, pumps, valves etc Hotel & leisure facilities supplement*
November 2011 Chilled beams December 2011 BMS & controls
Combined heat & power Lighting Supplement*
* = Supplements
Editorial submission: Please send editorial proposals/ ideas three months before publication date, eg, 1st October for January publication.
Send to:
editor@cibsejournal.com.
The fi nal editorial copy deadline is one month before publication date.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56