THE THERMAL SAFETY OF CHROMATICS PRODUCTS FOR
THE MIDDLE EAST
Summary:
The Middle East is a relatively aggressive area as far as the risk of thermal fracture for
opaque glazing is concerned: however, in many areas, Chromatics will be safe in many
applications, even in dark colours (which are the most vulnerable).
Introduction:
The surface of the Earth receives radiative energy from the Sun, the power of which can
be expressed in Watts per Square Metre (W/SqM or WM-2).
Figure one, below, shows the maximum solar power experienced in various parts of the
World:
Distribution Of Solar Radiation All Over The World
Up to 1000 W/SqM
Up to 750 W/SqM
Up to 650W/SqM
Figure one
A piece of Chromatics exposed to this radiation will naturally heat up, and if part of it is
shaded, or behind a frame, differential heating across the panel may be set up, with
resulting thermal stress. Such stresses can be calculated and risk of thermal breakage
assessed.
Major factors in these calculations include:
1. The Solar Radiation Power (the higher, the greater the risk);
2. The Stress Relieving Factor for the panel (the higher, the greater the risk);
3. The Safe Break Temperature (the lower, the greater the risk).
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Document Created by AR Walker
April 2009
The other major factor is Diurnal Temperature Range. This is simply the maximum
ambient temperature difference experienced in a particular geographical location in a
single day. In areas where this is high, glass panels will be relatively cold in the mornings
when the Sun comes up. This makes the risk of thermal breakage higher, whereas in
locations with a low diurnal range, the risk is proportionately lower. Note that a high
diurnal range does not necessarily mean a “hot” location: some tropical areas have
little difference in temperatures between day and night (low diurnal range), whilst some
areas in the far Northern latitudes have a very high diurnal range.
Figure two, below, shows the diurnal range around the World:
Figure two
By using these factors it is possible to calculate a “Basic Temperature Difference” for a
given piece of Chromatics in a given colour in a given geographical location: this is
then modified by a number of factors, including aspect, frame type & colour, type of
backup, any shading etc. etc. Because of the multiplicity of these factors, it is important
to recognise from the outset that it is impossible to give a general case answer, and
say, for instance, that the products will be safe in one geographical area, and not in
another. However, it is possible to give some general guidance, and to identify areas of
high or low risk of thermal fracture.
Procedure for making a thermal safety check:
1. Basic Temperature Difference (BTD) is calculated using the expression:
(For Single Glazing)
BTD = RI x α +DR x he
(he + hi)
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Where:
BTD
RI
α
DR
he
hi
=
=
=
=
=
=
Basic Temperature Difference
Radiation Intensity
Absorptance of the glass
Diurnal Range
External Heat Transfer Coefficient
Internal Heat Transfer Coefficient
(K)
(W/m2K)
(K)
2. A calculated temperature difference is then found by modifying the BTD
according to any factors present in the application – for example, static shadow,
blinds, different backup etc.
3. The final calculated temperature difference (FCTD) is then found by multiplying
the value obtained in 6, above, by the Stress Relieving Factor. (0.625 for
Chromatics)
4. Assessment of risk is now made by comparing the FCTD with the design strength
(51°K for Chromatics)
5. If FCTD ≤ 51°K, then the application is deemed to be safe
If FCTD > 51°K, then the application is deemed to be at risk of thermal fracture
Factors to be used:
Stress Relieving Factor: A Stress Relieving Factor (SRF) of 0.625 shall be used when
making an assessment of thermal safety (80 Micron foil)
Safe Break Temperature Difference (Design Strength): A Design Strength (DS) of 51°K
shall be used when making an assessment of thermal safety (80 micron foil)
The Middle East:
Let us now consider the region in question: the Middle East (Figure three):
Figure three
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Let us start by considering the Solar Radiation Intensity & the Diurnal Range
experienced by the region (Figure four):
Figure four
As can be seen, much of the region experiences rather high Solar radiation (orange &
brown areas) of 750-1000W/SqM. Most coastal areas on the Arabian Peninsula receive
around 800W/SqM.
In terms of Diurnal Range , apart from the South-West tip of the Yemen, all of the area
has a high range of 15-20K.
Thus, in broad terms, we can summarise the region into three distinct areas:
1. Coastal areas, receiving about 800 W/SqM with a diurnal range of up to 18K
2. Inland areas, receiving up to 1000W/SqM in the North, diurnal range of up to 20K
3. Inland areas, receiving up to 900W/SqM in the central Arabian Peninsula, diurnal
range of up to 20K
For these three ranges, the basic temperature difference for Chromatics can be
calculated:
REGION
BTD (White) BTD (Black)
Coastal Area
41.1
52.5
Inland Area
49.9
64.2
Central Arabian Peninsula
46.3
58.9
Table One
(Assumed: he=10 hi=8, glazed perpendicularly)
By taking the calculation further, we can reach final temperature differences – if
assumptions are made that will vary from building to building. Assume: no blinds,
backup factor=23, shading factor = 1.301, frame factor =0.75)
REGION
FTD (White) FTD (Black)
Coastal Area
39.7
46.8
Inland Area
45.2
54.2
Central Arabian Peninsula
42.8
50.8
Table Two
Comparing these numbers to the Safe Break Temperature (51K) it is clear that much of
the region will be a “safe” area for Chromatics.
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Specific locations:
Consider these key specific locations in the region:
Location Light Colours Dark Colours
Kuwait
■
■
Qatar
Bahrain
Oman
Jeddah
Dubai
Riyadh
Tehran
Istanbul
Cairo
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
Definitions: (Risk is for the Chromatics Products, not for any other type).
■ OK – final calculated temperature likely to be less than 45K
■ Calculation should be undertaken – final calculated temperature likely to be 45-48K
■ Calculation should be undertaken with particular attention to static shadow – final
calculated temperature likely to be 48-52K
■
Calculation must be carried out – final calculated temperature may be above 52K
These figures are indicative only, and we recommend that a thermal safety check is carried out using data
from a specific building design and location.
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Document Created by AR Walker
April 2009