How hot does a glass roof get?

[Dr Barnacle Luffy]

"dibs" pointed out that CT glass is made out of Alon a transparent ceramic aluminum. Aluminum has a very low emissivity coefficient for IR which means it is highly reflective. Thus may not need a coating of any kind. Would love to know what the emissivity coefficient for IR of Alon is.
"ajdelange" pointed out emissivity cart for infrared.

Advertisement

 

[carpedatum]

Tesla's been improving the heat management coatings it applies to glass roofs very steadily over the years. It's kind of easy to spot, on later models, because moisture on the roof (e.g. in the morning or in rain) causes the glass to look a bit more colorful.

https://www.carthrottle.com/post/teslas-weird-orange-glass-roof-is-layers-of-cool-science/

It has also been steadily improving the algorithms and hardware it uses to vent and cool the vehicle automatically when it is parked in the sun, while wasting as little energy as possible. If you can ever spot a lot of them parked together in the sun on a hot day, it is amusing to note how many of them will be sitting there with fans purring away.

On top of that you can cool the thing down before you get in, with your phone, and schedule that kind of thing in advance. I imagine by the time the CT rolls out, user control over cabin temp will incredibly flexible and easy, and the truck will also be learning your habits to help make sure you're pleased with cabin temps, without having to give it too much thought.

The glass roof is an awesome experience in current Teslas in part because Tesla continues to address the side-effects with rigor and creativity. I'm really looking forward to experiencing it in the CT.

 

[ReddykwRun]

-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

Reminds me of the old Apollo Lunar Lander, all wrapped up in Gold Foil like a bad Christmas wrap job.

 

[Dr Barnacle Luffy]

Tesla's been improving the heat management coatings it applies to glass roofs very steadily over the years. It's kind of easy to spot, on later models, because moisture on the roof (e.g. in the morning or in rain) causes the glass to look a bit more colorful.

https://www.carthrottle.com/post/teslas-weird-orange-glass-roof-is-layers-of-cool-science/

It has also been steadily improving the algorithms and hardware it uses to vent and cool the vehicle automatically when it is parked in the sun, while wasting as little energy as possible. If you can ever spot a lot of them parked together in the sun on a hot day, it is amusing to note how many of them will be sitting there with fans purring away.

On top of that you can cool the thing down before you get in, with your phone, and schedule that kind of thing in advance. I imagine by the time the CT rolls out, user control over cabin temp will incredibly flexible and easy, and the truck will also be learning your habits to help make sure you're pleased with cabin temps, without having to give it too much thought.

The glass roof is an awesome experience in current Teslas in part because Tesla continues to address the side-effects with rigor and creativity. I'm really looking forward to experiencing it in the CT.

It appears that they are extremely good at unlearning what they have learned and is key to their rapid innovation.

 

[ajdelange]

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.

Well you are right to do that. emissivity actually has little to do with it. My error. Not thinking clearly last night. Another little detail I thought I screwed up on but as it turns out I don't think I did is the linear relationship between power transfer and temperature. Over DC to daylight that goes as the 4th power of temperature but over a 2000 - 9000 nm range (where most IR cameras and thermometers work) it appears to be more linear though I need to keep checking on that.

Where the emissivity of glass comes in is that the camera in recording my image is receiving energy from me reflected from the glass at the same time the glass is throwing heat at the camera from the fact that it has high emissivity and is at room temperature. In order to estimate the reflectivity we have to go to temperatures high enough that the reflected energy swamps the black body radiation from the glass. Experiments today with such higher temperature suggest that reflectivity is only about 23%.

But IR does not pass through glass. That is easily demonstrated by putting a hot object on one side of a piece of glass and trying to photograph it in the IR band from the other. With that same kitchen door one cannot see a 233 °C hotplate from the other side. More to the point and what should be of more direct interest to readers here is that one cannot see the hot lights on the ceiling of my garage from inside my Tesla.

 

[Dr Barnacle Luffy]

Well you are right to do that. emissivity actually has little to do with it. My error. Not thinking clearly last night. Another little detail I thought I screwed up on but as it turns out I don't think I did is the linear relationship between power transfer and temperature. Over DC to daylight that goes as the 4th power of temperature but over a 2000 - 9000 nm range (where most IR cameras and thermometers work) it appears to be more linear though I need to keep checking on that.

Where the emissivity of glass comes in is that the camera in recording my image is receiving energy from me reflected from the glass at the same time the glass is throwing heat at the camera from the fact that it has high emissivity and is at room temperature. In order to estimate the reflectivity we have to go to temperatures high enough that the reflected energy swamps the black body radiation from the glass. Experiments today with such higher temperature suggest that reflectivity is only about 23%.

But IR does not pass through glass. That is easily demonstrated by putting a hot object on one side of a piece of glass and trying to photograph it in the IR band from the other. With that same kitchen door one cannot see a 233 °C hotplate from the other side. More to the point and what should be of more direct interest to readers here is that one cannot see the hot lights on the ceiling of my garage from inside my Tesla.

God I remember years and years ago in my first college physics class. We were talking about orbital mechanics. I rose my hand and said, "There has got to be a simple answer to this question." He responded, "Complex questions often have complex answers."

I found the specs for Aton- optical-ceramic

surmet.com/technology/alon-optcal-ceramic/index.php

Looked at the specs and determined that you would not see red crisp through the glass. Next page confirmed it. The last page they showed domes for IR servailance. What? how can that be and I am back to square one.

 

[Dr Barnacle Luffy]

At 74 my brain just doesn't run as fast as those younger than myself. But I was still able to study for and pass my exam for my FAA UAV license last year. Apparently, I need to brush up on my physics. Going to check out the classes on Brilliant.or... If I don't post, hopefully I am studying and have not kicked the bucket.

 

[ajdelange]

At 74 my brain just doesn't run as fast as those younger than myself. But I was still able to study for and pass my exam for my FAA UAV license last year.

I can, as they say, relate to that. I too did a "can I still learn" exercise too but in my case it was for the EPA HFC certification. Not only was I able to pass the test but the dividends have been huge. Not only have I been able to fix the bungles of my fellow certificate holders but have saved thousands on repairs over the years after buying all those neat digital manifolds, extraction machines, vacuum pumps etc. An unexpected benefit came when the gas igniter on our furnace went out during a cold snap late on a Friday afternoon (have you noticed it always happens on Friday especially if it is a 3 day weekend). So off I go to the local HVAC supply store, find the part on the shelf and take it up to the counter. "Company name?" says the clerk. I tell him it's personal. "Can't sell it to you." he says. "Why not. I've been doing business with you guys for 15 years." I say. "It's an electrical part." says he. "So what. I've got and advanced degree in electrical engineering" say I. "Doesn't matter. Store policy." At this point the guy working the adjacent register walks over and says "Do you have an HFC card?". When I said yes he said "Why didn't you say so?" and opened an account. The logic is evidently that someone who knows he should not release R22 also knows how to safely install an igniter in a furnace. WTF?

Apparently, I need to brush up on my physics. Going to check out the classes on Brilliant.or...

That's one of the things I love about the BEV revolution. So many different areas of EE, physics and chemistry come up. Here I am integrating the Planck equation in order to see if I am justified in my IR reflection estimates based on temperature estimates from IR images. I haven't done anything like that since I tried to find submarines by looking at radiometric estimates of ocean surface temperature many many years ago, Nostalgic, interesting and it keeps the rust out of the hinges

 

[Dr Barnacle Luffy]

I think where I got off coarse was when I was raising plants under LED lighting. I had to add IR LEDs or thier leaf surface temperature would not get high enough and they would do poorly. The Planck equation says every wavelength has energy. But, I got the idea that no energy was transferred unless it hit a resonant body.

 

[ajdelange]

Remember Compton scattering? It's been a long time but I think that might be the explanation.

 

[Dr Barnacle Luffy]

My inital understanding was Compton scattering explains what happens but not necessarily why. I will dive deeper.

 

[ajdelange]

As I say it's hazy but I think the seminal finding was that photons have momentum which they can transfer to other particles (such as an atom or an electron or even another photon) thus increasing the target's kinetic energy (temperature) with the energy lost by the photon resulting in shift to lower frequency (longer wavelength).

 

[Dr Barnacle Luffy]

ajdelange, I sent you mail (started a conversation with you)

yes it explains what happens but I am interested in why it happens.
I postulate that every molecule has it's own unique harmonic signature. Kind of like the signature of a heart beat but on a molecular level. Compton demonstrated what happened with an x-ray and said that it would be true from visual light through x-ray. He did not explain why one target would exchange energy and why another would not. I postulate that the packet has to be able to resonate with some part of the target's signature for the packet to exchange energy.

 

[ajdelange]

Each molecule in a particular state has its wave function dependent on a whole bunch of quantum numbers and, being very broad, recall that Borne hypothesis says that probability density function of one of the molecules parameters depends on the magnitude of the wave function operated on by some operator. The simplest example, and to be honest the only one I understand at all, would be the wave fuction of the hydrogen with a single electron in the ground state. That wave function consists of a set of concentric spheres. Thus the aziumuth and elevation of an electron are uniformly distributed (i.e. the electron is equally likely to be at any "latitude" or "longitude" but its distance from the nucleus is not distributed uniformly, It is more likely to be at a particular distance from the nucleus than it is to be at twice that distance. Thus the chance of a photon aimed at a hydrogen atom may or may not collide with its electron. It is completely a probability game.

 

[Dr Barnacle Luffy]

Each molecule in a particular state has its wave function dependent on a whole bunch of quantum numbers and, being very broad, recall that Borne hypothesis says that probability density function of one of the molecules parameters depends on the magnitude of the wave function operated on by some operator. The simplest example, and to be honest the only one I understand at all, would be the wave fuction of the hydrogen with a single electron in the ground state. That wave function consists of a set of concentric spheres. Thus the aziumuth and elevation of an electron are uniformly distributed (i.e. the electron is equally likely to be at any "latitude" or "longitude" but its distance from the nucleus is not distributed uniformly, It is more likely to be at a particular distance from the nucleus than it is to be at twice that distance. Thus the chance of a photon aimed at a hydrogen atom may or may not collide with its electron. It is completely a probability game.

maybe I misled you, it has been some time since I tried to communicate with someone on this level. I am talking about compounds not individual atoms. I do not have the equipment in my lab to go past spectroscopy on discovery.