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REAPING THE BENEFITS AVOIDING THE PITFALLS

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

CIBSE/ASHRAE Meeting

LSBU May 12th 2004
Martin Ratcliffe LSBU/Roger Preston Environmental 1

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0bjectives • Show that glazing
– is important for occupant well being and productivity – can reduce energy consumption – can lead to thermal & visual discomfort

• Give guidelines on design of glazing
Martin Ratcliffe LSBU/Roger Preston Environmental 2

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The Balancing Act

PASSIVE SOLAR HEATING AND DAYLIGHT

EXCESSIVE COOLING/HEATING

VIEW OUT / IN

THERMAL DISCOMFORT AND GLARE

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Well-Being

• View Out • Preference for Natural Light

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Well-Being

• Feel Valued • In touch with outside world • Photophysiological Effects

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Well-Being

• Increase in Productivity

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Daylight

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

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Daylight Factor

Indoor Illuminance Outdoor Illuminance

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Daylight

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Daylight and glazing
daylight transmittance 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 clear low e clear with blinds (closed) ipasol 52/29 strongly heat absorbing
10

Martin Ratcliffe LSBU/Roger Preston Environmental

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Lighting Energy

potential energy savingswithdimming photoelectriccontrol020406080100012

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Overall Energy

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The Solar Process
Re-emitted

absorbed absorbed

Reflected SHORTWAVE LONGWAVE

absorbed absorbed

Directly Transmitted Re-emitted

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Total Solar Gain

= directly transmitted (shortwave) + re-emitted (longwave)

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Shading Coefficient

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

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Solar Heat Gain Factor “g-value” Total Solar Gain Incident Solar Intensity

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Peak Solar Gains - UK

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Peak Solar Gains - UK

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Thermal Comfort- Radiant Temperature
LONGWAVESHORTWAVE

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SHORTWAVE

depends on
– transmittance of glass – external shading – internal shading – sun position

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

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Maximum Dry Resultant Temperature 100% glazing 38 36 34
Dry resultant temperature

includes shortwave solar radiation

32 30 28 26 24 22 20 1 3 5 7 9 11 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 Strongly heat absorbing double glazing

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Frequency of occurrance of dry resultant temp at 2m from the glazed facade
2500 3.5m BS 2000 includes direct solar 5m BS

Hours per year

1500

1000

500

0 25 26 27 28 29 30 31 32 Dry resultant temperature

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Asymmetric radiation
LONGWAVESHORTWAVE

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ISO 7726

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Variation in Asymmetric Radiation with distance from window and Glass Surface Temperature 30 25 CIBSE max 20 15 10 5 0 0 2 4 6 8 10 distance from window, m
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100% Glazing to one wall, blinds closed, sunny day

Asymetric Radiation,

o

C

50oC 45oC 40oC

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

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flexibility Want a glazing system that can cope with this:

Variable solar performance

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Possible solutions? • Ventilated cavity • Adjustable external shading • photochromic

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Ventilated cavity
Warm air out

G=0.15

Cool air in

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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
Martin Ratcliffe LSBU/Roger Preston Environmental 31


				
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