PV in glazed facadesThermal indoor climate

Søren Østergaard JensenIndustry and EnergyTeknologisk Institut

PV in glazed facades

First some theory

2 and 3 D heat losses

directly transmitted solar radiation

absorption

convection

long wave radiation

infiltrationconduction

reflection

Simple theory

heat loss – U-value [W/m2K]

directly transmitted light and solar energy

indirectly transmitted solar energy

absorbedsolar energyreflected

solar energy

solar radiation

transmittance for light – τ-value incoming solar energy – g-value heat loss – U-value

Parameters in the simple theory

PV-cells have impact on the g-value PV-cells haven’t impact on the U-value the U-value has impact on the g-value

Parameters in the simple theory

1 pane of clear glass 0.85 2 panes of clear glass 0.75 3 panes of clear glass 0.65 2 panes clear glass with low-e coating 0.60-0.65 Windows with solar screening 0.25-0.50

Examples of g-values

g-value

The PV cells are mounted in the external pane of a low-e window with Argon between the two glass

Product opening g-value light trans- area mittance Würth WSS0007 8% 0.13 0.06 Würth WSS0008 21% 0.19 0.15 Würth WSS0009 22% 0.20 0.16 MSK / Suntech MST-44T101OU 10% 0.13 0.07 MSK / Suntech MST-50T051OU 4% 0.11 0.04 Interpane – reference panel 31% 0.23 0.22

U-value: 1.2 W/m2K

Windows with PV-cells

The PV cells are mounted in the external pane of a traditional window with air between the two glass

Product opening g-value light trans- area mittance Würth WSS0007 8% 0.23 0.07 Würth WSS0008 21% 0.30 0.16 Würth WSS0009 22% 0.30 0.17 MSK / Suntech MST-44T101OU 10% 0.23 0.07 MSK / Suntech MST-50T051OU 4% 0.20 0.04 Interpane – reference panel 31% 0.34 0.23

U-value: 2.8 W/m2K

Windows with PV-cells

Example: small office building

Heated floor area: 650 m2

Window area: 31 % of heated floor area

Influence of the g-værdi

0

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

g-værdi

ener

gy

dem

and

[kW

h/m

2]

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cooling demand

heating demand

number of hours above 26 C

Influence of the U-værdi

0

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120

0.5 1 1.5 2 2.5 3 3.5

U-værdi

ener

gy

dem

and

[kW

h/m

2]

0

50

100

150

200

250

300

350

400

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ho

urs

cooling demand

heating demand

number of hours above 26 C

Cold down fall

U-valueWindow: 1,5 W/m²KWall: 0,2-0,4 W/m²K

”Cold down fall”

Solar shading

Solar shading

g-valueNu 0.17Suncool 0.32Float 0.65

PowerShades