Glass Roof - This is not how it's supposed to work

[TeeEmCee]

Just stepped outside to grab something from the car. I got in and felt that the glass roof was as hot and annoying as ever, so I grabbed an IR gun and measured its temperature. Below you have the reported temperature for the top part of the windshield and that of a spot on the roof equally close to the front crossbeam (to account for eventual heat radiating from the metal).

The app reports the car interior temperature to be 94 F and it's 84 F outside, halfway cloudy. The car had been sitting outside for a couple of hours and the AC had been running for a few seconds since it turned itself on when I unlocked the car. The sun incidence angle was more shallow for the windscreen, but I suspect that had little effect since the car's been sitting long enough to allow the windshield to collect enough energy. The temperature difference (estimated by simply touching the glass) was consistent with what I felt on every sunny day drive so far.

Windshield:

Roof:

 

[Lasairfion]

Being from the UK, I'm a bit confused.





What is this "sun" thing you keep talking about?

 

[diamond.g]

Is the temp from the other side the same?

 

[TeeEmCee]

Is the temp from the other side the same?

Well, that is a very good question. Let me go check.

 

[SMAlset]

When you roof gets wet does it have the red glow to it?

 

[TurnFast]

We've packed up the sun in the Seattle area, it's nothing but gray skies and rain for the next 9 months here.
However I can report the glass roof does well with mid 50s weather.

If you live in a climate that is still mid 80s in October, maybe getting a little more tint on the roof would help?

 

[TeeEmCee]

It's been cloudy for the last 20 mins and it cooled down a bit.

Same spots measured from outside:

Windshield:

Roof:

 

[Eno Deb]

I'm not sure what's so surprising about this. The tinted glass lets less energy into the interior than the untinted windshield. Part of the difference is reflected, the other part absorbed by the dark glass. The latter heats up the roof.

 

[eprosenx]

Also note that those IR thermometers depend on the reflectance properties of the surface you point them at. Mine has a calibration option to try to adjust for the surface you point it at.

I wonder if pointing at the part of the roof glass that has the red coating vs. the part without the coating makes a difference in the accuracy of the reading. (Also the coating might result in different temperatures for different parts of the glass)

 

[TeeEmCee]

When you roof gets wet does it have the red glow to it?

Yes. Just the top panel, not the back window. Looks like the back window is worse (measured from inside again).

Top of rear window:

Roof panel:

 

[Kirby64]

Also note that those IR thermometers depend on the reflectance properties of the surface you point them at. Mine has a calibration option to try to adjust for the surface you point it at.

I wonder if pointing at the part of the roof glass that has the red coating vs. the part without the coating makes a difference in the accuracy of the reading. (Also the coating might result in different temperatures for different parts of the glass)

Was just about to note this. Don't trust IR thermometers on surfaces that are either clear or shiny. Metal's are particularly bad. You won't get an accurate reading unless you adjust the emissivity property, which I guarantee that thermometer won't do. Or if it does, it won't do it by default and you'll have to figure out the emissivity of the glass you're measuring (which I guarantee is different between the windshield and the tinted sunroof).

 

[TeeEmCee]

I'm not sure what's so surprising about this. The tinted glass lets less energy into the interior than the untinted windshield. Part of the difference is reflected, the other part absorbed by the dark glass. The latter heats up the roof.

Exactly. The point of the advertised IR protection though is not to keep the seats from heating up a couple extra degrees and radiate the better part of that energy onto my head. As it is, it's providing some marginal protection to air conditioned interior surfaces while ruining the driver and passenger comfort.

A proper design would recognize the fact that humans most enjoy having hot ass and cool head, not the other way around.

 

[Eno Deb]

One interesting experiment might be if you could drive into a shaded location and quickly measure the temperature again. This would exclude any residual IR from the sun that might get through the tinted glass, i.e. you'd measure only the radiant heat from the glass itself. If the tint works as well as advertised, the difference should be small.

 

[S4WRXTTCS]

I would test it with a thermocouple, and not IR.

 

[SMAlset]

Since hot air rises and the windshield and side windows are generating heat inside, I kind of would expect the glass roof inside to be hotter. No where for the heat to go, but it should mix with the AC cooled air and cool off quickly. Maybe a tint shop can give you a better idea if the IR on the roof glass is as expected.

I recall a thread on here where someone was told that there are 3 glass manufacturers for the windows in the Model 3 and the companies incorporate their IR treatment somewhat differently so the appearance might not be uniform across the roof but the IR is there. My back window is also "black" and not "red". It's also a window with a larger surface than the front driver/passenger roof window so may trap in more heat at the interior surface of it.

 

[gtmotor]

After going through one of the hottest summers on record in Arizona I can say I'm happy with my glass roof. Everyone is always amazed at how little heat comes through it...

 

[TeeEmCee]

After going through one of the hottest summers on record in Arizona I can say I'm happy with my glass roof. Everyone is always amazed at how little heat comes through it...

Very hot weather may mean AC blasting harder than it does for me this time of year and therefore creating enough draft to cool the roof somewhat. I also don't like the AC blowing straight at my face and split the jet and have it go around me. You probably don't do the same.

All I can say is this is in line with most everything else about Teslas. Way cool (not the temperature kind of cool), but otherwise half-baked. My audis have even larger panoramic roofs. The glass gets just as hot at times but, when it does, I just close the rolling sunshade and I never get any uncomfortable heat radiating from above.

I spoke to a number of people about this problem and some opined that an extra layer of IR-rejecting film would do nothing (might even overheat and crack the glass). Since I don't care to get into glass roof design and fix Tesla's product, I just bought that crummy-looking mesh insert. I bet it will help, but it does nothing for the back seats.

 

[SMAlset]

Let us know if you think the sunshade helps.

 

[Twiglett]

pretty sure that's exactly how its supposed to work.
IR coating prevent the transmission of infrared, but it can't prevent heat transfer from conduction.
Just been through the usual hotter than Hades Texas summer without issues or a roof shade

 

[Uncle Paul]

Measuring the temp of the roof is missing the point.

The coating is supposed to reduce the IR going into the vehicle.

Better to get a reading off a seat surface that is getting direct sun.

It is designed to take some load off the Airconditioning system, and reduce radiant heat to keep the occupants more comfortable.