[ingliz]

the external heat source has been removed

No, it hasn't.

The sun radiates heat to earth in the day. At night the reverse happens when the warmer earth radiates heat to the cold night sky.

[Truth To Power]

No, it hasn't.

Yes it has:

The sun radiates heat to earth in the day. At night the reverse happens when the warmer earth radiates heat to the cold night sky.

See? You agree that at night, the heat source has been removed.

[Truth To Power]

Blocking air is not a heat source.

<yawn> Do you feel warmer with a blanket on your bed or not?

Energy does not magically appear from blocking air movement.

Blocking warm air from leaving a place makes the blocked place warmer. There's nothing magical about a blanket. People buy them and use them because they work. I'm not sure there is any clearer or simpler way to explain that to you.

You need a source of energy.

The sun is the energy source.

[Pants-of-dog]

<yawn> Do you feel warmer with a blanket on your bed or not?

Not at first. This is because the sheets are cold and are absorbing heat that is radiating from my body.

Eventually it heats up for several reasons. The most important one is the insulating effect of the duvet and thick blankets. Blocking convection is not significant in comparison.

Blocking warm air from leaving a place makes the blocked place warmer. There's nothing magical about a blanket. People buy them and use them because they work. I'm not sure there is any clearer or simpler way to explain that to you.

Blocking air exfiltration is only one aspect of how to stop heat transfer through convection. Greenhouses do not, for example, block the movement of interior air inside the building. They only stop the movement of interior air through the building envelope, and even that is intermittent.

The sun is the energy source.

Exactly.

Greenhouses work (i.e. heat the interiors) by exploiting solar radiation.

[ingliz]

the heat source has been removed

No, it has not.

The source of the heat is still the Sun stored heat or not. The Sun heated the earth.

And the heat source is still 'external' to the greenhouse; the carport itself is unheated.

[Truth To Power]

No, it has not.

Yes, of course it has. You are just denying a self-evident and indisputable fact of objective physical reality because you have already realized that it proves you wrong.

The source of the heat is still the Sun stored heat or not. The Sun heated the earth.

But at night, the sun is not shining. It has been removed. You know this. Of course you do. You are just denying a self-evident and indisputable fact of objective physical reality because you have already realized that it proves you wrong.

And the heat source is still 'external' to the greenhouse; the carport itself is unheated.

Right: it's unheated because the heat source has been removed. You are just denying a self-evident and indisputable fact of objective physical reality because you have already realized that it proves you wrong.

[Pants-of-dog]

@Truth To Power

If you are arguing that the sun is the heat source for a greenhouse, then you are agreeing with us and contradicting your previous claim that greenhouses are heated by blocking exfiltration of air.

[ingliz]

@Truth To Power

At night the IR radiates from the ground. There is no radiation* entering the carport/greenhouse from above.

The cars outside remain frosty.

The car inside the wall-less greenhouse is frost-free.

All the cars receive the same dose of radiation from the ground.

The only difference in experimental conditions experienced by the outside cars and the inside car is the carport roof.

The only heat source (radiation) that can heat the inside car sufficient to keep the car frost-free is the backscatter from the ceiling of the wall-less greenhouse.

The only heat source (radiation) lacking outside is the backscatter from the ceiling of the wall-less greenhouse.





* Not strictly true as there is moonlight, but the effect is minuscule.

[QatzelOk]

...the heated air inside the greenhouse reaches the roof, the heated air will transfer this heat to the glass which makes up the roof...

Interesting that you provide this description without noticing that the materiality of the greenhouse is very different than the materiality of the earth's atmosphere.

You often use metaphorical comparisons without noticing when they fall apart. I think this is due to lack-of-big-picture reasoning.

Logic isn't a game of chess where *words* are the playing pieces.

[ingliz]

@QatzelOk

I thought we were discussing how greenhouses work, in this particular instance, not the atmosphere.

[Truth To Power]

@Truth To Power

At night the IR radiates from the ground. There is no radiation* entering the carport/greenhouse from above.

So you're saying a greenhouse doesn't heat up at night?

Who'd a' thunk it?

The only difference in experimental conditions experienced by the outside cars and the inside car is the carport roof.

Have you done this experiment with a glass greenhouse roof that blocks IR and a polyethylene one that doesn't? Until you have (and we both know that you have not), you are just bloviating.

The only heat source (radiation) that can heat the inside car sufficient to keep the car frost-free is the backscatter from the ceiling of the wall-less greenhouse.

The only heat source (radiation) lacking outside is the backscatter from the ceiling of the wall-less greenhouse.

You don't understand the mechanism by which the greenhouse roof stops the car from getting frosty. It doesn't keep the car warm (easily proved with a thermometer). It just stops condensing water vapor falling out of the air from reaching the car; an IR-transparent polyethylene roof does it just as effectively. If you were right, and the IR from the roof was doing it, then the roof itself would also not be getting frosty, as it can't make the car warmer than it is itself. But the greenhouse roof does get frosty, proving you wrong and me right. Inevitably.

You may consider yourself schooled.

[ingliz]

@Truth To Power

Wrong.

The roof of the greenhouse exposed to the winter air is frosty. Inside it's frost-free in all but the coldest winters.

The ground, water butts, trestles, etc., in a greenhouse, radiate IR at a rate of approx 75 watts per square meter* at night, and most of that is being re-radiated, back into the greenhouse, glass being practically opaque to radiation with a wavelength higher than 5 µm.

It just stops condensing water vapor falling out of the air from reaching the car

Of course, it does because warm air holds more water.

An unheated greenhouse can keep overnight temperatures as much as 5°C warmer than outside.





* If the temperate zone's surface radiation winter average is about 81 W/m^2, then the day/night numbers work out to about 7.7% variation between them, about 87 W/m^2 during the day and about 75 at night. That's a pretty good estimate I think. I'm open to a better estimate if someone can think of a way to do it.

[ArthurTandy1]

No, it hasn't.

The sun radiates heat to earth in the day. At night the reverse happens when the warmer earth radiates heat to the cold night sky.

There is no such thing as the sky. There is only space outside the Earth.

[Pants-of-dog]

So you're saying a greenhouse doesn't heat up at night?

Who'd a' thunk it?

Have you done this experiment with a glass greenhouse roof that blocks IR and a polyethylene one that doesn't? Until you have (and we both know that you have not), you are just bloviating.

Do you have a link to such an experiment?

Because your last link did not. It merely looked at the U value of the two materials, as well as the IR transmittance.

You don't understand the mechanism by which the greenhouse roof stops the car from getting frosty. It doesn't keep the car warm (easily proved with a thermometer). It just stops condensing water vapor falling out of the air from reaching the car; an IR-transparent polyethylene roof does it just as effectively. If you were right, and the IR from the roof was doing it, then the roof itself would also not be getting frosty, as it can't make the car warmer than it is itself. But the greenhouse roof does get frosty, proving you wrong and me right. Inevitably.

You may consider yourself schooled.

Frost does not collect on things because water vapour falls on things.

First of all, water vapour does not fall. Even when water vapour condenses in midair, it becomes mist or fog. It does not fall. If enough water vapour condenses out at the same time, it would fall as rain or snow. But that is obviously not what you meant, unless you are arguing that it snows or rains inside greenhouses.

Besides, the warm air inside the greenhouse would stop the water from “falling” because warm air holds more water.

The roof collects frost because water vapour condenses on the bottom of the glass. Note that this is impossible if the water vapour fell out of the air, since things do not fall upwards.

It also disproves the claim that greenhouses work by blocking convection, since this warm moist air loses heat to the cool roof glass after travelling to the underside of the roof through…..you guessed it, convection.

[Truth To Power]

@Truth To Power

If you are arguing that the sun is the heat source for a greenhouse, then you are agreeing with us and contradicting your previous claim that greenhouses are heated by blocking exfiltration of air.

Why always choose to be wrong? The sun is equally the source of heat for both the greenhouse and the open field beside it. The greenhouse is just warmer than the open field because it blocks heat loss via convection.

[Pants-of-dog]

Why always choose to be wrong? The sun is equally the source of heat for both the greenhouse and the open field beside it. The greenhouse is just warmer than the open field because it blocks heat loss via convection.

So when you said that a greenhouse works by blocking convection and not by radiation, you meant it works by blocking exfiltration and it also works by solar radiation.

[Truth To Power]

So when you said that a greenhouse works by blocking convection and not by radiation,

I said it works by blocking convection, not INFRARED radiation.

you meant it works by blocking exfiltration and it also works by solar radiation.

It works by admitting visible-spectrum sunlight that heats the ground, which heats the air just above it, and then blocking the resulting convective current that would otherwise let the warm air escape to the open atmosphere.

[Pants-of-dog]

@Truth To Power

I know what you said, and I was explaining what you should have said to make it clearer and more correct.

And once again, the convection inside the greenhouse is not blocked. The air circulates from the ground to roof and then back again, transferring heat from the ground to the roof.

[Truth To Power]

I know what you said,

Then why did you misstate it?

and I was explaining what you should have said to make it clearer and more correct.

No, what I said was clear and correct. You changed it to make it unclear and incorrect.

And once again, the convection inside the greenhouse is not blocked.

Right: the convection INSIDE the greenhouse is CREATED by the roof BLOCKING convection to the open atmosphere.

See how that works?

The air circulates from the ground to roof and then back again, transferring heat from the ground to the roof.

So you are saying that would happen just the same if the roof wasn't there??? Or are you only claiming that it would happen just the same if the roof was made of staggered layers of glass that blocked IR radiation but allowed the warm air to escape?

[late]

@Truth To Power

I know what you said, and I was explaining what you should have said to make it clearer and more correct.

And once again, the convection inside the greenhouse is not blocked. The air circulates from the ground to roof and then back again, transferring heat from the ground to the roof.

He'll keep shoveling BS as long as he keeps getting paid...