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53
Thermal resistance of materials
The thermal resistance of a slab of homogeneous material is calculated
by dividing its thickness by its thermal conductivity:
R = l/X
where R is the thermal resistance (m
2
K/W), / is the thickness of the
slab (m) and A is the thermal conductivity (W/mK). Resistance to
heat flow by a material depends on its thickness, density, water con-
tent and temperature. The latter two parameters result from the ma-
terial's location within the structure. Insulating materials are usually
protected from moisture and the possibility of physical damage as
they are of low density and strength. The thermal conductivity of
masonry can be found from the bulk dry density and the moisture
content, which depends on whether it is exposed to the climate or is
in a protected position.
Block B
Lexical exercises
I. Answer the questions:
1. What factors are included in the decision on the siting of a heat
emitter?
2. Why may the water in large heating systems be pressurized?
3. How do heating systems alter the mean radiant temperature of a
room?
4. What safety precautions are taken in buildings occupied by very
young, elderly, infirm or disabled people?
5. How can radiant heating minimize fuel costs while providing com-
fortable conditions?
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