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R = THERMAL RESISTANCE FOR THICKNESS GIVEN, HR- SQ.FT. °F/BTU
U = COEFFICIENT OF HEAT TRANSFER, BTU/ HYR./SQ.FT./°F
K= THERMAL CONDUCTIVITY, BTU-IN./HR./SQ.FT/°F
- Conduction is the transfer of heat through a solid object.
A good example would be how the elements on an electric stove or clothes
iron work. The molecules stay cool until they are restricted and start
to bump one another. This action causes energy to be released in the
form of heat. The faster heat moves through a material the higher its
conductivity.
- Convection is the transfer of heat by the movement of a flowing
medium such as water, air, etc. When you hold hand over a light bulb
and feel the heat rising through the air, you are experiencing the convection
process.
- Radiation is a direct transfer of heat from one object to another
without a heating medium in between. This is the same process by which
infrared heat works. Radiant energy is transmitted as an electromagnetic
wave until it strikes an object. Silver or foil act as a radiant barrier.
The main component of insulation is trapped air. These air spaces help to block
the transfer of heat. The better the material is at not conducting heat, the better
the insulation. Insulation works to keep heat in and out.
The basic types of insulation are:
- Fibers: Loosely woven to trap air (fiberglass, wool).
- Foam: Air bubbles trapped in a resin or solidified plastic material
(polyurethane and polystyrene).
- Particles: Loosely placed small pieces allowing for air spaces (sawdust,
cellulose).
The Alternative Buildings Yurt system has the following values:
- 0.17 R value - outside air film
- 0.08 R/inch - fiberglass
- 8.00 R/inch - high-density expanded polyurethane foam
- 0.08 R/inch - fiberglass
- 0.62 R value - inside air film
Our panels are comprised of 3" foam with an R value of 8 R/inch R = 24.
Every material in the home will offer some type of
insulative properties or values. This value can be expressed as the coefficient
of heat transfer (U) or the resistance to heat loss (R). The values are
inversely proportional, or U = 1/R. So the lower the U value, the better
the insulation and the higher the R value, the better a material resists
heat loss. Resistance can even be expressed as the inverse of conductivity
(K) or R = 1/K.
These numbers will help determine the effectiveness of a building envelop in protecting
your living space from losing too much energy.
Air exchange is a very important feature for the new
energy efficient home. Building envelopes have become so tight that indoor
air quality can suffer if no ventilation is present. Replacing stale,
humid air with fresh air that will reduce humidity and create a more comfortable
air motion is necessary. You may achieve this by passive ventilation --
opening your windows and doors -- or by using active ventilation fans.
Alternative Buildings Yurt systems are very tight and need
to be ventilated. Smaller units may use passive ventilation while our
large home-sized units will need an "air exchanger" to help move the old
humid air out and fresh air in.
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