How hot does a glass roof get?

[ajdelange]

Cornell. But this physics I learned by getting into and out of various vehicles with sun roofs in warm/hot weather.

I almost said "Lookup greenhouse effect on the Web" but if you do that you will get pages and pages on global warming. Before people worried about such things (or there was a web) it meant this to a physicist:

"The greenhouse effect refers to circumstances where the short wavelengths of visible light from the sun pass through a transparent medium and are absorbed, but the longer wavelengths of the infrared re-radiation from the heated objects are unable to pass through that medium. The trapping of the long wavelength radiation leads to more heating and a higher resultant temperature. Besides the heating of an automobile by sunlight through the windshield and the namesake example of heating the greenhouse by sunlight passing through sealed, transparent windows, the greenhouse effect has been widely used to describe the trapping of excess heat by the rising concentration of carbon dioxide in the atmosphere." (http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/grnhse.html)


I gather from your tone that you are questioning what I have said. Look up the emissivity of glass. Stand in front of a window and take a picture with an IR camera.

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[Dr Barnacle Luffy]

Please site where you learned your physics and then perhaps we can have a conversation.

To answer your first question: "Why would you want to do something like this?"

Right now it is 111 degree F outside here at my ranch. It can get up to 129 degrees F during the summer. I can understand how someone who lives in a town where everyone lives under a waterfall might ask "Why would anyone want to build a shower in there house?" Here you can tell a local from an outsider because the local is standing in the shade even if it is only cast from a telephone pole. The outsider is standing in the sun complaining how hot it is. There are many types of glass here we are talking about Tesla Bullet proof glass. I do not know its composition. If is is a layered polycarbonate. I know from past experience that polycarbonate has a memory and my be why Elon's window broke. I disagree with your statement that IR is reflected by glass and would like you to site where you got your information. It is reflected by plexyglass.. The reason it is not used for solar water heaters.

 

[Dr Barnacle Luffy]

Cornell. But this physics I learned by getting into and out of various vehicles with sun roofs in warm/hot weather.

I almost said "Lookup greenhouse effect on the Web" but if you do that you will get pages and pages on global warming. Before people worried about such things (or there was a web) it meant this to a physicist:

"The greenhouse effect refers to circumstances where the short wavelengths of visible light from the sun pass through a transparent medium and are absorbed, but the longer wavelengths of the infrared re-radiation from the heated objects are unable to pass through that medium. The trapping of the long wavelength radiation leads to more heating and a higher resultant temperature. Besides the heating of an automobile by sunlight through the windshield and the namesake example of heating the greenhouse by sunlight passing through sealed, transparent windows, the greenhouse effect has been widely used to describe the trapping of excess heat by the rising concentration of carbon dioxide in the atmosphere." (http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/grnhse.html)


I gather from your tone that you are questioning what I have said. Look up the emissivity of glass. Stand in front of a window and take a picture with an IR camera.

Not sure where you are going but I will follow your lead. Did you read the article I sited at #39?

 

[Dr Barnacle Luffy]

thermoworks.com... emissivity chart

no reflectivity= 1.0, 100% reflective 0.0
Glass: .92
Pollished Aluminum .05
Water:.95
Distilled water .95
Human skin... .98
It did not have gold. but it think it is some were around .03
It also did not have silver but I will google these because will be nice to know.

This only seems to suggest that glass reflects very little IR I believe the article you have sited is pseudoscience trying to explain global warming. oops climate change...

I have a 100 x 30 foot greenhouse It is covered in plastic that has been dopped to keep out UV

I have a sun oven that uses tempered glass.

Perhaps the article you read neglected to state that the glass in the greenhouse had been treated.

 

[Dr Barnacle Luffy]

ya, pretty cool. I can't wait to get the samples. Since spacex is blowing up so many proto types, I hope it has brought down the price of scrap SS sheets. Hoping to buy some 12x12 inch squares. Put a thermometer under them and test with the different coatings.

 

[Dids]

Please site where you learned your physics and then perhaps we can have a conversation.

He is right. Visible light hits interior and is retransmitted at lower energy where the glass absorbs and reflects it. Typical glass has high ir absorb which is why it's hella hot in the sun..... BUT. CT will be using armored glass which is believed to be Alon which is not glass at all. It is transparent ceramic aluminum. It transmits UV to mid IR. I know you are thinking oh no now I will fry in the heat but instead of the it being trapped inside it just passes through the roof. CT will be a much cooler vehicle. Even cooler than a solid metal roof.

 

[Dr Barnacle Luffy]

He is right. Visible light hits interior and is retransmitted at lower energy where the glass absorbs and reflects it. Typical glass has high ir absorb which is why it's hella hot in the sun..... BUT. CT will be using armored glass which is believed to be Alon which is not glass at all. It is transparent ceramic aluminum. It transmits UV to mid IR. I know you are thinking oh no now I will fry in the heat but instead of the it being trapped inside it just passes through the roof. CT will be a much cooler vehicle. Even cooler than a solid metal roof.

Thank you for the info on the CT glass.

 

[ajdelange]

I disagree with your statement that IR is reflected by glass and would like you to site where you got your information.

Well I got it at Cornell many years ago, I've gotten it over the course of 60 years practicing as an engineer, I've gotten it every time I stepped into a greenhouse or a warm car on a cold but sunny winter day, and when I step into a hot car on a summer day even if it isn;t that sunny, I've gotten it every time I pick up a book on spectroscopy and etc. You might as well ask me where I got F = m*a or I = E/R. And every time I try to look into the yard with night vision goggles without opening the window. This is one of those things that one learns in high school or college and carries with him the rest of his life. So if you want to find a reference that's going to be your job, not mine. Start with a basic physics text,

What I would ask you to do, given that you don't believe IR is reflected by glass, is to ask yourself why IR cameras don't have glass lenses. I would also ask you to explain what you are seeing in this picture:

It should be clear from the picture that it is a "selfie" but not one taken with the camera pointed at me but rather at a mirror. The mirror, however, is not a silvered one. It is just a sheet of glass in an interior door with a dark hallway behind it, Note that the chandelier behind me in the room I am standing in had actually been turned off for several minutes when the picture was taken.

Now where this gets really interesting is when we look not just at the image but at the temperatures on it. My skin temperature is about 35 °C i.e. 328K. The temperature of my forehead in the picture is 26 °C ~ 319.7K. The power in a band B is simply k*T*B. Bolzmann's constant and the bandwidth are the same before and after the reflection so k*328*B strikes the glass from some pixel sized spot on my forehead but only k*319.7*B reaches the corresponding spot on the camera CCD. Thus 319.7/328 = 0.974695 is the measured emissivity of this piece of glass. 97.4% of the IR striking it was reflected and 2.6% went through. If you look up the emissivity of glass you will find values in the 0.92 to 0.97.

 

[ajdelange]

I do not know its composition. If is is a layered polycarbonate. I know from past experience that polycarbonate has a memory and my be why Elon's window broke.

Just noticed this bit. I have no idea as to whether the incorporation of polycarbonate had anything to do with shattering but I thought were were trying to get you to understand that glass reflects infrared, Although there was no intent to include anything about polycarbonate when I took the IR picture I'll note that the lenses in my glasses are polycarbonate. The picture makes it obvious they block IR too.

 

[Dr Barnacle Luffy]

Well I got it at Cornell many years ago, I've gotten it over the course of 60 years practicing as an engineer, I've gotten it every time I stepped into a greenhouse or a warm car on a cold but sunny winter day, and when I step into a hot car on a summer day even if it isn;t that sunny, I've gotten it every time I pick up a book on spectroscopy and etc. You might as well ask me where I got F = m*a or I = E/R. And every time I try to look into the yard with night vision goggles without opening the window. This is one of those things that one learns in high school or college and carries with him the rest of his life. So if you want to find a reference that's going to be your job, not mine. Start with a basic physics text,

What I would ask you to do, given that you don't believe IR is reflected by glass, is to ask yourself why IR cameras don't have glass lenses. I would also ask you to explain what you are seeing in this picture:

It should be clear from the picture that it is a "selfie" but not one taken with the camera pointed at me but rather at a mirror. The mirror, however, is not a silvered one. It is just a sheet of glass in an interior door with a dark hallway behind it, Note that the chandelier behind me in the room I am standing in had actually been turned off for several minutes when the picture was taken.

Now where this gets really interesting is when we look not just at the image but at the temperatures on it. My skin temperature is about 35 °C i.e. 328K. The temperature of my forehead in the picture is 26 °C ~ 319.7K. The power in a band B is simply k*T*B. Bolzmann's constant and the bandwidth are the same before and after the reflection so k*328*B strikes the glass from some pixel sized spot on my forehead but only k*319.7*B reaches the corresponding spot on the camera CCD. Thus 319.7/328 = 0.974695 is the measured emissivity of this piece of glass. 97.4% of the IR striking it was reflected and 2.6% went through. If you look up the emissivity of glass you will find values in the 0.92 to 0.97.

I usually walk away form a confrontation. I have obviously cased you some discomfort. For which I truly apologize. I do not intentionally go around trying to jack people up. However, I still disagree with you.

 

[Dr Barnacle Luffy]

ajdelang

I do not question your credentials. I don't know many people that would even know what a emissivity chart was. I do question how you are interpreting the data on the chart.

 

[Dr Barnacle Luffy]

My interests are in mods for a Desert CT. This admittedly is a small knitch market. I think it might be less confusing if I started a new thread called "mods for a Desert CT"

If you agree please leave a "like". If you don't please leave a unhappy face. If you don't care please leave a big eyes face. Thanks

 

[Newton]

-if im reading correctly, the thought was gold wrap for heating the exterior metal less?

sounds like a win/win. Im cooool and look like a baller

 

[Dr Barnacle Luffy]

-if im reading correctly, the thought was gold wrap for heating the exterior metal less?

sounds like a win/win. Im cooool and look like a baller

You are correct. Two interesting things have come up in this thread. I need to go back through the threads so I can site the correct people that came up with the information.

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