1. Internal environment in ETFE foil covered building enclosures
James Ward and John Chilton
School of Architecture, Design and Built Environment
Nottingham Trent University
Alex Heslop and Lance Rowell
Architen Landrell Associates
16 September 2010
TensiNet 2010 Sofia

2. Outline Introduction Thermal/optical properties of ETFE foil
Design considerations for ETFE-covered enclosures
Visible light transmission and quality
Internal environment
Overheating
Ventilation
Glare
Noise levels
Conclusions
Photo: Alastair Gardiner
16 September 2010
TensiNet 2010 Sofia

3. Introduction A recent conference paper highlighted:
“Limited research regarding the modelling of ETFE in building applications and limited availability of information on material properties...”
It also pointed out that:
Previous ETFE studies have focused mainly on structural properties and related issues, while little research has been carried out in order to determine energy transmission properties and characteristics in terms of environmental building design.
Source: Poirazis, Kragh and Hogg (2009)
16 September 2010
TensiNet 2010 Sofia

4. Thermal/ optical properties of ETFE foil
Source: Dyneon™ Fluorothermoplastics Product Comparison Guide (2009)
16 September 2010
TensiNet 2010 Sofia

5. The properties of ETFE
80 µm clear
100 µm clear
150 µm clear
200 µm clear
100 µm white
200 µm white
light transmittance
0.93
0.91
0.9
0.45
0.37
light reflectance
0.07
0.08
0.09
0.5
0.59
solar direct transmittance
0.94
0.92
0.55
0.47
solar reflectance
0.06
0.39
solar absorbence
0.01
total solar transmittance
0.57
0.49
short-wave shading coefficient
1.08
1.07
1.06
1.05
0.63
0.54
long-wave shading coefficient
0.03
0.02
total shading coefficient
0.66
0.56
UV transmittance to 380 nm
0.88
0.86
0.83
0.76
UV transmittance to 400 nm
0.89
0.87
0.79
0.13
mean solar gain factors
0.85
0.84
0.52
sample thickness (mm)
0.082
0.105
0.155
0.206
0.097
0.205
Source: ETFE Foil Cushions as an Alternative to Glass for Roofs and Atria
Source: (2000)
16 September 2010
TensiNet 2010 Sofia

6. Design Considerations
ETFE foil is increasingly seen as the ‘wonder’ material for lightweight structural enclosures.
Some issues that affect architectural design decisions are:
Visible light transmission and quality
Internal environment
Overheating
Ventilation
Glare
Noise levels
Photo: Alastair Gardiner
16 September 2010
TensiNet 2010 Sofia

7. Light transmission and quality
Transmittance depends on the wavelength of incident radiation but for ETFE foil is fairly consistent over the visible spectrum nm.
This provides interior colour rendering close to that of natural daylight.
Ultraviolet light transmission (below 380nm) is higher than for glass and polycarbonate.
This has benefits for solaria and swimming pools and also for greenhouses.
Infra-red transmittance is also high for wavelengths up to about 7000nm.
16 September 2010
TensiNet 2010 Sofia

8. Measured transmittance ETFE 200μm samples
16 September 2010
TensiNet 2010 Sofia

9. Measured long-wave infrared transmittance of 200μm ETFE sample
2500
25000
10000
7000
Courtesy: Professor Wayne Cranton, NTU
16 September 2010
TensiNet 2010 Sofia 9

10. Internal Environment
ETFE cushions are still a relatively new solution for covering courtyards and atria.
Poor performance is sometimes inappropriately ascribed to the system rather than other aspects of the design.
Basic properties of the ETFE foil can be modified by fritting and low-emissivity coatings.
16 September 2010
TensiNet 2010 Sofia

11. Fritting to modify transmittance
Frit Ref #
Description
Ink Trans %
Coverage %
Trans %
n/a
Clear 200μ ETFE 87 1
Large dots 23 20
74.2 2
Static lines 28 30
69.3 3
Camo 35
64.6 4
Clouds 32 46
61.7 5
Med dots 50
59.5 6 55 7 62
47.32 8
Hex 70
45.7 9
Inverse Camo
42.2 10
Chequered 75 39
16 September 2010
TensiNet 2010 Sofia

12. ‘Intelligent’ fritting
Lancaster University, ISS Building, 2009
Architect/Designer: Wilson Mason Main Contractor/Customer: John Turner and Sons
16 September 2010
TensiNet 2010 Sofia

13. Overheating
The U-value and solar heat gain coefficient, or g-value, for glass and ETFE are often quoted as being quite similar.
U-value
(W/m2K)
g-value
6mm monolithic glass
5.9
0.95
Double Glazing Unit (DGU)
2.8
0.83
High Performance DGU
2.0
0.35
2 Layer ETFE Cushion
2.9
(with frit)
3 Layer ETFE Cushion
1.9
4 Layer ETFE Cushion
1.4
Glass and ETFE cushion thermal/solar data as cited in Poirazis, H., Kragh, M. And Hogg, C. (2009)
16 September 2010
TensiNet 2010 Sofia

14. Values are often taken to be interchangeable even though the physical characteristics may be different.
ETFE Atrium Roof
Thickness (mm)
Transmittance (%)
Layer Description
Clear Float 6
0.78
Cavity 12
Shading Device
None
EN-ISO U-value: glass only (Wm-2K-1)
1.9
EN-ISO U-value: inc. frame (Wm-2K-1)
G-value (BS EN 410):
0.30/0.74
Example of design data assumed by building services consultant for ETFE covered new-build atrium in the UK, May 2010.
16 September 2010
TensiNet 2010 Sofia

15. Kingsdale Comprehensive School, London, where, with the use of intelligently fritted three-layer cushions designed to reduced transmittance to as low as 5%, when necessary, and the provision of extensive high-level cross-ventilation, summer temperatures at high level were kept below 35°C, compared to up to 45°C predicted by initial thermal modelling.
[Source: Building Services Journal, 09/04, CIBSE, London, 09/2004, pp ]
16 September 2010
TensiNet 2010 Sofia

16. Nottingham Boys High School
2009
Architects: Maber Architects, Nottingham
ETFE cushion system: Architen Landrell Associates Ltd
16 September 2010
TensiNet 2010 Sofia

17. 16 September 2010
TensiNet 2010 Sofia

18. 16 September 2010
TensiNet 2010 Sofia

19. 16 September 2010
TensiNet 2010 Sofia

20. Nottingham Boys High School
2009
Architects: Maber Architects, Nottingham
ETFE cushion system: Architen Landrell Associates Ltd
16 September 2010
TensiNet 2010 Sofia

21. Ventilation
As with glazed atria, appropriate ventilation is essential.
Also, care must be taken in planning of occupied spaces to avoid the potential stratified layer of hot air immediately under the roof.
16 September 2010
TensiNet 2010 Sofia

22. 16 September 2010
TensiNet 2010 Sofia

23. Glare
Although translucent, ETFE foil does not have the transparency of glass.
In the following example, due to the orientation and the configuration of the enclosure (enveloped with ETFE foils) under strong sunlight it created an internal environment that was uncomfortable to remain in for any extended period of time.
This is chiefly due to light levels far in excess of any of the adjoining rooms or corridors (glare) and, in summer, the elevated internal temperature.
16 September 2010
TensiNet 2010 Sofia

24. William Smith Building, British Geological Survey
2008/9
Architects: Maber Architects, Nottingham
ETFE cushion system: Vector Foiltec
16 September 2010
TensiNet 2010 Sofia

25. 16 September 2010
TensiNet 2010 Sofia

26. Noise levels
Due to the taut drum-like nature of tensioned ETFE and ETFE cushions; in heavy rain there is a chance that a level of noise is reached that could be considered unacceptable in occupied areas under the cushion array.
This may be addressed with the application of an external mesh to attenuate the noise created by rain droplet impacts.
16 September 2010
TensiNet 2010 Sofia

27. 16 September 2010
TensiNet 2010 Sofia

28. Conclusions
Unlike for glazing, there are few readily identifiable sources available for universally applicable information pertaining to ETFE foil cushions.
Given the bespoke nature of most ETFE enclosures it is difficult to designate standard values
This leads to three possibilities:
Test each configuration for each enclosure.
Designate a standard cushion profile and for it construct ISO testing specifications based on existing specifications for physical and theoretical determination of attributes.
Increase knowledge of the properties of ETFE cushions to ensure ‘thermal models’ take into account the varying profiles and account for them.
16 September 2010
TensiNet 2010 Sofia 28

29. Conclusions
The current understanding of the thermal/optical properties of ETFE foil is somewhat limited.
The environmental performance of spaces such as atria enclosed by ETFE cladding is also sometimes poorly understood.
There is a clear need for further research in both of these areas.
16 September 2010
TensiNet 2010 Sofia 29