I How does BTU convert to heat in degrees in a greenhouse?

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The discussion highlights that the sun provides approximately 200 BTU per square foot in winter when directly perpendicular to greenhouse glass or plastic, with losses increasing at steeper angles. Calculating the greenhouse temperature at solar noon suggests a potential rise from an average of 50 degrees to 75 degrees during the day, though temperatures can drop to 25 degrees after dark. Winter plants can tolerate temperatures as low as 0 to -20 degrees, but growth halts below 40 degrees. The idea of building a test model with a visible thermometer is proposed to validate these temperature predictions. Additionally, factors like snow or cloud cover can significantly impact greenhouse heating effectiveness.
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Information online claims sun is 200 btu per sq ft in winter only when sun is perpendicular to plastic or glass of a green house. When sun hits glass or plastic at an angle there are losses. The steeper the angle the more losses will be.

Is it possible to calculate how warm a green house will get in full sun at solar 12 noon.?

Our average day temperature is now about 50 degrees a temperature rise for 25 degrees will make it 75 degrees in a green house tunnel during the day only. It will still get 25 degrees after dark. Winter plants are good down to 0 to -20 degrees but nothing grows below 40 degrees.

If I can prove on paper this will work then i will build it.
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Why not build a test model with some sort of thermometer inside that can be read visually from the outside?

One thing to be aware of is snow or cloud cover may further reduce its effectiveness.

In Texas, we would cover our plants with plankets. However where the plant leaves touched the planket we would see the effects of frost.
 
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