Thermal insulation for heat retention
comes as no surprise that well-insulated buildings consume considerably
less energy for heating.
Roughly 40% of energy used in
Europe today is for space heating in buildings. This is a significant
cost for households and businesses. It uses scarce energy resources and
contributes to carbon dioxide and other greenhouse gas emissions that
are important factors in global warming.
consume considerably less heat energy. Not only can mineral wool help to
considerably decrease heating bills but it can also help to make an
important contribution to reducing European greenhouse gas emissions.
Better insulation warms the
home - not the planet. Thus the intelligent, forward-looking use of
energy is dependent on the optimum use of thermal insulation.
Often the costs of installing
suitable thermal insulation will have been paid off in the form of lower
utility bills within a few months. The average energy 'payback' of a
building insulated to recommended standards is from 1 to 12 months. 450
million tonnes of CO2 could be saved annually through thermal
insulation and practical energy savings.
Thermal Insulation for Low Temperatures
Keeping heat out and
maintaining low temperatures is just as vital a role for effective
insulation as heat retention. Indeed many of today's industrial
processes can only be carried out in controlled cold environments. But
generating low temperatures is even more costly than producing heat. A
lot of storage takes place at low temperatures and a lot of insulation
is used for this.
Increasingly important within Europe is the role of mineral wool in
insulating air conditioned, cooled space applications within office and
Meeting the demand for thermal
insulation for low temperatures has been perhaps the single most
important driving force behind the continuing technological development
of insulating materials. Products using mineral wool have consistently
proved to be the most cost effective solution.
The basics of heat transfer
The principles of heat transfer
help to understand how insulation works. Heat flows from warm to colder
surfaces until the temperature of both is equal.
These flows can take three forms:
Conduction is the direct
transfer of heat between adjoining molecules. A warmer molecule
transfers some of its energy to colder neighbours. A good example is
when one sits down on a cold metal chair, one can feel the cold from
the chair as heat from the warmer body is quickly transferred by
conduction to the chair.
Convection is the transfer
of heat through liquids and gases. An example is warm air rising
from a hot surface and being replaced by cooler and denser air that
sinks. Heat is carried away from the surface by the warm air.
Radiation is the
transmission of energy through space by electromagnetic waves.
Radiated heat moves at the speed of light through the air without
heating the space between, just as one feels the warmth of the sun
on one's face, heat radiates from the sun to earth without heating
the space between.
Mineral wool thermal insulation
prevents convection by holding air still in the matrix of the wool.
Still air is a good insulator. Mineral wool also stops radiation and
limits the conduction of heat through the body of the insulation. The
effectiveness of the mineral wool in reducing heat transfer depends upon
its structural properties such as density, thickness, composition and
the fineness of the wool as well as the temperature at which it is used.
The heat transfer through
insulation is a combination of solid and gas conduction, convection and
radiation. This gives a thermal conductivity versus density
characteristic which is non-linear and has a minimum.
How well a material transmits
heat through itself is known as thermal conductivity.
Thermal conductivity, l,
(lambda, measured in watts per meter per degrees Kelvin, W/mK) of a
material represents the quantity of heat that passes through a meter
thickness per square meter per time unit with one degree difference in
temperature between the faces.
The Lambda value compares the
ability of materials to transmit heat through them under these fixed
conditions. The lower the lambda value the better the insulator the
material will be. (Lambda values of typical materials are for example,
Copper 380 W/mK, Aluminium 210 W/mK; Steel 46 W/mK; Wood 0.21 W/mK;
Mineral wool 0.045 W/mK; Air 0.026 W/mK).
For construction purposes a
material is defined as insulating if it's thermal conductivity is less
than 0.065 W/mK. A typical mineral wool has l of 0.035-0.040.
The insulation capacity of the
mineral wool products is based on the low thermal conductivity of air in
the pockets of the wool material.
Thermal resistance or R value,
is a measure of the ability of a given thickness of a material to
prevent the passage of heat. The thermal resistance, R, of a material
with thickness, d (meters) and thermal conductivity, l, is equal to R=
d/l (Units are square meters degrees Kelvin per Watt (m2K/W).
Thermal resistance, R, is the
inverse of the coefficient of thermal transmission whilst thermal
conductivity is an inherent property of a material.