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Plexiglas, Glass, Greenhouse Materials
Name: Nicholas
Status: other
Grade: 12+
Location: NY
Country: USA
Date: N/A
Question:
The greenhouse effect (not an environmental reference, but an
actual greenhouse, made out of glass) is very efficient at retaining
infra-red light which heats the house. Does Plexiglas have the same
infra-red retention capabilities? If so, what is the common ground
between the two very different materials that provides this ability?
Replies:
Nicholas,
Greenhouses actually work by a somewhat different mechanism than the
environmental greenhouse effect. Although there is some trapping of
infrared, greenhouses primarily work by allowing visible light in (for
which glass or Plexiglass or even plastic sheeting can be made
transparent), as the light is absorbed by the environment (plants and
ground), energy is radiated out (convection) in the form of heat. The
heat is then trapped by the greenhouse structure. There is some energy
transmitted in the form of infrared, but this is minor as can be shown
by simply opening a small window on the roof of a greenhouse and noting
that the temperature within drops considerably (more than can be
accounted for by escaping infrared). Thus, the only requirement for
greenhouse material is that it be transparent to visible light, and be
sealed so that convection is maintained within the structure. Additional
considerations such as infrared reflectiveness, roof angles, and conduction
can be addressed for efficiency purposes, but are less important.
Greg (Roberto Gregorius)
Canisius College
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Update: June 2012
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