Martin Ratcliffe Visiting Research Fellow, Centre for Energy Studies at LSBU Head of Roger Preston Environmental

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1 REAPING THE BENEFITS AVOIDING THE PITFALLS Martin Ratcliffe Visiting Research Fellow, Centre for Energy Studies at LSBU Head of Roger Preston CIBSE/ASHRAE Meeting LSBU May 12th

2 Show that glazing 0bjectives is important for occupant well being and productivity can reduce energy consumption can lead to thermal & visual discomfort Give guidelines on design of glazing 2

3 The Balancing Act PASSIVE SOLAR HEATING AND DAYLIGHT EXCESSIVE COOLING/HEATING VIEW OUT / IN THERMAL DISCOMFORT AND GLARE 3

4 Well-Being View Out Preference for Natural Light 4

5 Well-Being Feel Valued In touch with outside world Photophysiological Effects 5

6 Well-Being Increase in Productivity 6

7 Daylight About 100 Lumens per Watt (artificial lighting = 50 Lm/W) 7

8 Daylight Factor Indoor Illuminance Outdoor Illuminance 8

9 Daylight 9

10 Daylight and glazing daylight transmittance clear low e clear with blinds (closed) ipasol 52/29 strongly heat absorbing 10

11 Lighting Energy potential energy savingswithdimming photoelectri 11

12 Overall Energy 12

13 The Solar Process Re-emitted absorbed SHORTWAVE LONGWAVE Reflected absorbed Re-emitted Directly Transmitted 13

14 Total Solar Gain = directly transmitted (shortwave) + re-emitted (longwave) 14

15 Shading Coefficient SC = SWSC + LWSC Solar Gain through actual glazing Solar Gain through clear single glazing 15

16 Solar Heat Gain Factor g-value Total Solar Gain Incident Solar Intensity 16

17 Peak Solar Gains - UK 17

18 Peak Solar Gains - UK 18

19 Thermal Comfort- Radiant Temperature LONGWAVESHORTWAVE 19

20 SHORTWAVE depends on transmittance of glass external shading internal shading sun position 20

21 Longwave Depends on glass/blind surface temp glazing absorptance window area distance from glazing 21

22 Maximum Dry Resultant Temperature 100% glazing 38 Dry resultant temperature includes shortwave solar radiation Distance from glazing (m) Clear double glazed low E Clear double glazed low E with internal blinds Double glazed interpane 52/29 Double glazed interpane 52/29 with internal blinds Triple glazed ventilated cavity 22

23 Frequency of occurrance of dry resultant temp at 2m from the glazed facade includes direct solar 3.5m BS 5m BS Hours per year Dry resultant temperature 23

24 Asymmetric radiation LONGWAVESHORTWAVE 24

25 ISO

26 Variation in Asymmetric Radiation with distance from window and Glass Surface Temperature % Glazing to one wall, blinds closed, sunny day o C Asymetric Radiation, CIBSE max 50oC 45oC 40oC distance from window, m 26

27 flexibility! Solar gains vary with Weather conditions Time of year Time of day 27

28 flexibility Want a glazing system that can cope with this: Variable solar performance 28

29 Ventilated cavity Possible solutions? Adjustable external shading photochromic 29

30 Ventilated cavity Warm air out G=0.15 Cool air in 30

31 summary Opportunity to reduce energy consumption Improve occupant well being Improve productivity Potential for discomfort on sunny days Standard calculations not sufficient Need an adaptable system of solar control 31