Solar
greenhouses, as their name suggests, utilize energy from the sun in
order to meet their temperature needs. The solar radiation from the
sun passes through their surfaces to heat the ground. The greenhouse
design then traps this energy in order to maintain the higher temperature
it needs.
The walls and ceiling of these useful structures also serve to prevent
the warmer air within from mixing with the cooler air without. A more
technical way of saying this is that they prevent convection (heat transfer
through moving gas or liquid) and conduction (transmission of heat from
particle to particle within solids) from equalizing inner and outer
temperatures.
Solar greenhouses will also serve to control internal temperature by
controlling the transparency to the solar and terrestrial thermal radiation
bands.
For a warmer temperature than the surrounding environment, more transparency
is presented to the solar radiation band. At the same time, more resistance
to the thermal radiation band serves to trap the heat. A surface that
is more reflective to solar energy while less restrictive to the thermal
radiation band will of course have the opposite effect- a cooler environment
than the sounding temperatures.
Generally, solar greenhouses are utilized for the purpose of creating
a warmer environment. For this, a material is chosen which absorb some
of the infrared (IR) radiation which is leaving the space. A portion
of this will be radiated back into the greenhouse. As a result, there
is less energy lost to the sky than would happen without such a structure.
So it can be seen that both heatloss through conduction and IR can be
discouraged with good insulation and glazing which absorbs infrared
radiation.
Another effective aspect to solar greenhouses is the optimized usage
of the soil base. A portion of the available heat during daytime will
be absorbed by this mass. At night, this becomes a source of radiant
heat. If the enhancement of this effect is desirable, it is possible
to do so by installing tubing for subterranean air circulation.
In addition to this, while a subterranean design can provide heating
at night, it can also encourage cooling during the daytime through this
same method of absorption. Another method of encouraging this same effect
of absorption include utilizing storage materials with a high capacity
for heat. Bins of sand and rock or containers of water are such examples.
Greenhouse overheating during the daytime can be prevented while the
temperature during the more cool periods, such as night, can be maintained
simply and effectively.
It is not very surprising that as both human civilization and science
progress, better and better design develops as well. Solar greenhouses
benefit greatly from the newest and latest plastic surfaces and glazing
options. With better material and design, a greenhouse owner is better
able to control both the wavelengths of incoming solar radiation as
well as those of outgoing thermal infrared radiation. Better insulation
for the reduction of the conductive loss through glazing is another
area which sees ongoing achievement. Some owners will even use a "greenhouse-in-a-greenhouse"
technique to provide extra warmth where it is needed in particular.
