Post on 31-Mar-2015
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
10
20
30
40
50
60
70
80
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]
0
50
100
150
200
250
300
350
400
ho
urs
cooling demand
heating demand
number of hours above 26 C
Influence of the U-værdi
0
20
40
60
80
100
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
450
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