What is Thermal Insulation?
Insulation is defined as a material or combination of materials which retard
the flow of heat. The materials can be adapted to any size, shape or surface.
A variety of finishes are used to protect the insulation from mechanical
and environmental damage, and to enhance appearance.
Where
is Mechanical Thermal and Acoustical Insulation Installed?
Mechanical thermal insulations are materials that insulate the components
of mechanical systems in commercial buildings and industrial processes. In
buildings such as shopping centers, schools, hospitals, and hotels, mechanical
insulations are installed to improve the energy consumption of the buildings'
cooling and heating systems, domestic hot and chilled water supply, and
refrigerated systems including ducts and housings.
For
industrial facilities, such as power plants, refineries, ethanol plants, and paper mills,
mechanical thermal insulations are installed to control heat gain or heat
loss on process piping and equipment, steam and condensate distribution
systems, boilers, smoke stacks, bag houses and precipitators, and storage
tanks.
Functions
of Insulation
Insulation is used to perform one or more of the following functions:
•Reduce heat loss or heat gain to achieve energy conservation.
•Protect the environment through the reduction of CO2 , NOx and greenhouse
gases.
•Control surface temperatures for personnel and equipment protection.
•Control the temperature of commercial and industrial processes.
•Prevent or reduce condensation on surfaces.
Increase operating efficiency of heating/ventilation/cooling, plumbing,
steam, process and power systems.
•Prevent or reduce damage to equipment from exposure to fire or corrosive
atmospheres.
•Assist mechanical systems in meeting USDA (FDA) criteria in food
and pharmaceutical plants.
•Reduce noise from mechanical systems.
Understanding
Heat Flow/Heat Transfer
In order to understand how insulation works, it is important to understand
the concept of heat flow or heat transfer. In general, heat always flows
from warmer to cooler surfaces. This flow does not stop until the temperature
in the two surfaces is equal. Heat is 'transferred' by three different
means: conduction, convection and radiation. Insulation reduces the transference
of heat.
Conduction
Conduction is direct heat flow through solids. It results from the physical
contact of one object with another. Heat is transmitted by molecular motion.
Molecules transmit their energy to adjoining molecules of lesser heat
content, whose motion is thereby increased. For example, when people first
sit down on cold metal chairs, they instantly feel the discomfort that
comes from the contact of a warm body with a cold chair as body heat is
quickly transferred from the skin, and through clothing, to the chair
by conduction.
Convection
Convection is the flow of heat (forced and natural) within a fluid. A
fluid is a substance that may be either a gas or a liquid. The movement
of a heat- carrying fluid occurs either by natural convection or by forced
convection as in the case of a forced-air furnace. For example, people
usually detect a draft when standing close to a single glazed window in
the winter. Air within the room tends to stratify so that the air near
the ceiling is warmer because it has become less dense when heated and
so it rises. This is natural convection. That warm air loses heat to the
vertical window because heat flows from hot to cold. This air becomes
cooler and denser, so it begins to sink. This is the draft felt by people
and is another example of natural convection. Warm air entering a room
from a supply duct is an example of forced convection.
Radiation
Radiation is the transmission of energy through space by means of electromagnetic
waves. Radiated heat moves at the speed of light through the air without
heating the space between the surfaces. An example is the warmth you feel
on your skin from the sun. The sun is unbelievable hot, and the space
between it and us is still unbelievable cold.
How Insulation Works
The basic requirement for thermal insulation is to provide a significant
resistance path to the flow of heat through the insulation material. To
accomplish this, the insulation material must reduce the rate of heat
transfer by conduction, convection, radiation, or any combination of these
mechanisms.
