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Friday, November 4, 2011

A Greenhouse Effect?

I will probably delete this post in favor of the one linked above. For now, I will leave things as they are.

A Greenhouse Effect

Quite a few people have and intend to experiment with how the Greenhouse effect works, in simulated greenhouses. Woods did his experiment. A Vaughan Pratt did his experiment. Myth Busters did their experiment. I think even Al Gore commissioned an experiment. What do all these experiments have in common? None of them were actual Green Houses.

While a greenhouse gets its warmth from the sun it is the retention of that warmth that makes a greenhouse useful. The warmth it retains is from the surface or ground. In addition to proper greenhouses, there are also cold frames and a variety of other methods used to retain surface heat. Plants need sunlight to survive, so a greenhouse can’t use highly efficient insulation to retain heat, it has to use less efficient transparent materials. In very cold climates, these transparent materials need to include double glazing and if one can accord, triple glazing, to prevent excess heat loss to the environment.
Greenhouse are also equipped with ventilation systems to prevent over heating in the day, which damages the plants watering and misting systems to maintain humidity and in some cases, CO2 injection to improve plant growth rate.
So if someone wants to study a greenhouse, why not use a greenhouse?

Simple experiment number 1. Build two greenhouses of identical construction. In the first, till the soil and plant directly in the ground. In the second, insulate the ground and provide a moisture barrier. Then plant in pots or use hydroponics. Since the solar input is roughly the same, why is the second so much less efficient? There ya go, the surface is the source of the heat we are trying to retain.

Since some labs have limited space, how would you simulate a greenhouse accurately on a small scale?
Tip one, not by shine heat lamps on poor unsuspecting items, but by simulating a surface source with a upper sink and measuring how conduction, convection and radiant heat flow are all impacted. The percentage of each is the greenhouse effect, just as it is in our atmosphere.
Since our atmosphere has layers, why not include layers in your greenhouse effect experiment.

Comments are misbehaving again, either spammers or Foxfire issues:


True, the question is what are the limits? A true greenhouse seem to be just a more applicable model for determining those limits. A nursery would allow more ventilation if it became too warm. The atmosphere seems to have the same option. The tropics for example.

If there is not enough sunlight, the greenhouse doesn't work, the Antarctic for example.

Things have to be tuned for best performance, the Northern hemisphere for example.

So other than opening a window, what else can be done to control temperature in a Northern hemisphere greenhouse? More plants? More water? Less water? A nurseryman on a budget may grow more tomatoes and fewer impatients. In other words, land use may have a much greater impact than estimated.

1 comment:

  1. If greenhouse has some benefits then naturally, it has some effects also. Everybody knows the effects of greenhouse which may be harmful.