When compared against the benefits of modern living…………….

” when an IR photon is absorbed by something it ceases to exist and cannot be reemitted” Not really. When a photon is absorbed by say CO2, the molecule can return from the excited state by emitting a photon of exactly the same energy that was absorbed. Is it the same photon that went in? Since we can’t label photons, the question really is moot.

Solar e
nergy can be transmitted, reflected or absorbed by the greenhouse covering. The transmitted
portion of the visible (PAR) light is needed for plant growth, but only a small fraction (1
–
5%) is
actually utilized by the plant. The unused PAR (and the remainder of the solar radiation other than
PAR) is absorbed by the plant and the greenhouse internal components (soil, concrete) and structure.
The absorbed energy, warms the components, and they reemit the energy as infrared (IR) heat, and
warm the greenhouse air. This “greenhouse heating effect” is the welcome result of radiation transmission into a closed space, and the prevention of some of the heat from leaving through the cover
of the space

The more insulated the cover of the greenhouse, the lower ra
te of heat lost, and thus the easier to
maintain air temperature in the cool season. The insulating ability of transparent coverings is primarily
dependent on whether it is a single or double
–
layer. This obviously is a very important consideration
when s
electing a glazing where supplemental heating is required. If the cover is constructed of two
layers (for example, double
–
layer, air
–
inflated PE, or structured two
–
layer rigid PC), then it can insulateagainst heat loss better than a single layer (for example glass, or PC). Always select a double-layermaterial over a single-layer for greater heat energy savings. Double-layer covers will require less solar energy in the day, and fossil fuel energy at night, to maintain the inside air temperature, than will singlelayer covers during the cool season.

However, the night heating costs can be further reduced if the cover has an additive that acts as an
infrared heat barrier (low transmission of infrared radiation). Glass has traditionally had an excellent
barrier to infrared transmission, but the plastic film covers (such as PE) may not. The IR barrier
improves the “greenhouse heating effect” by trapping the IR radiation so that it can be absorbed within
the greenhouse for warming the air, instead of pass
ing through the glazing to the outdoor environment

no.. this is not right… if you dont want to start growing earlier in the season, then i guess you can forgoe the IR blocking which makes it warmer which makes for an extended growing season.

but even if the air was still, the temperature would even out. see the laws of thermodynamics. (and note that they are not even correct as they are actual special laws, not general laws – so they have caveats. Sci Amer did a great article on this part of them)

the only way to prevent convection is to have even temperature. where the temps are not even, you get convection… as warmer air is thinner than colder air, and we live in a gravity field. though i guess in space, you can avoid convection as well being in microgravity.

now that is referring to boyant convection, but diffusion is also convection… and there is no way to stop this process in the circumstances of a green house.

same is true of our atmosphere as a whole, convection moves air from the surface, to higher areas till it pushes the heat out to space, and then cools and drops again. such convective events are waht powers hurricanes, tornadoes, updrafts that can cause a plane ride to become a roller coaster, etc.

NYer: no, I don’t have such a blog. I would suggest reading wattsupwiththat.com on a daily basis. Anthony has at the top of the page a reference section for all the relevant data. A treasure trove of factual material. Dr. Roy Spencer is another valuable resource http://www.drroyspencer.com/