Physical Properties
Light Transmission
The sunlight which reaches the surface of the earth has a wavelength
that ranges between 295 - 2140 nanometers (10-9
meters). This wavelength range is divided into the following sections:
| UV-B Middle ultraviolet region |
280 - 315 nm |
| UV-A Near ultraviolet region |
315 - 380 nm |
| Visible light region |
380 - 780 nm |
| Near infra-red region |
780 - 1400 nm |
| Middle infra-red region |
1400 - 3000 nm |
As shown in the Figure below, Multiwall PC sheet has the maximum transmission
in the visible light region.
Despite transmitting visible light very well, Multiwall PC sheet
is almost opaque to radiation in the UV and far infra-red region. This
useful shielding property can prevent discoloration of sensitive
materials such as fabrics or other organic materials placed under or
behind UV protected PC sheet glazing: e.g. a factory warehouse,
museum or shopping center., exterior and interior partitions.
Fig. 5
Temperature Increase Inside the Building
The same properties, in combination with the insulating multiwall
structure, contribute to a temperature increase inside the building.
Sunlight entering the building heats the air both directly and through
absorption by framework, furniture etc., and is released as infra-red
energy. The insulating properties of Multiwall PC sheet prevents this
heat from escaping faster than it is created, causing a temperature
increase - the so-called 'greenhouse effect'. The temperature can be
controlled by venting often in combination with specialty solar control sheet like
Polygal's Polycoolite®.
Solar Control
Transparent grades of Multiwall PC sheet have excellent light transmission,
between 64 and 82% depending upon thickness. However, for buildings
in hot climates or with south facing aspects, Multiwall PC sheet is
available in solar control grades of , solar control grey, blue, green and
opal white. These grades significantly reduce solar heat build up, helping
to maintain comfortable interior temperatures.
The specially tinted and non-glare sheet cuts down the brightness of sunlight to
a pleasing level and reduces air conditioning costs in the summer.
Solar Heat Gain
The solar radiation reaching the sheet is reflected, absorbed and transmitted,
as shown in Figure 6. The greatest proportion is transmitted and the
total solar transmission (ST) is the sum of the direct transmission
(DT) and the inwardly released part of the absorbed energy (A). Table
7 outlines the overall solar control properties of the Multiwall PC sheet .
Fig. 6
Fig. 7 Compare by dividing Light transmission/Solar
Transmission. The higher the value, the better the control of solar heat
gain.
| Total Solar Transmission (ST) in % |
| Material |
TW6
2RS |
TW8
2RS |
TW10
2RS |
TW16
3TS |
TW16
2NS |
TW16
4RS |
TW20
5RS |
| Clear 112 |
86 |
86 |
85 |
82 |
82 |
80 |
75 |
Bronze
|
5109
51914
515055 |
60
55 |
60
35 |
60 |
55 |
55 |
55 |
55 |
| White |
825074
825075
82995 |
50
30
76 |
50
30 |
30 |
71 |
71 |
71 |
65 |
