Summer Months - MPG Benefit from Tint?

[kuzzi]

So, it's starting to get warm in the Southern States and the A/Cs are starting to run hard.

 

We have found from another thread that a large improvement may be made to economy when the A/C is under low load.

 

Tint can help to keep the temps down, but enough to see a significant increase in economy?

 

I had hoped to maybe document this over the summer by getting tint halfway through, but maybe others can chime in.

 

Thoughts/Opinions? Admittedly, it would be pretty weird to see a 5+ mpg improvement just by making the windows darker, but maybe there's some proof out there.

[acdii]

You dont need to make them darker, just the UV blocking itself can help keep the heat down inside. It is strange when you think about it though, dark colors absorb heat, yet darkening the windows, makes it cooler? So when you think about it that way, is it really the darkerness, or is it the UV blockage?

[kuzzi]

You dont need to make them darker, just the UV blocking itself can help keep the heat down inside. It is strange when you think about it though, dark colors absorb heat, yet darkening the windows, makes it cooler? So when you think about it that way, is it really the darkerness, or is it the UV blockage?

I should have known better than say darker. Ran a project in college using different light sources through various filters to see what the end light spectrum result was. Used multiple "clear/opaque" filters that blocked IR and UV ranges. Cannot remember what they were, but some were VERY expensive.

 

As far as I know, it is only IR that causes the heat in the vehicle, it is absorbed by the seats/dash/etc and transferred to the air in the car. Cracking windows can help to circulate the hot air out, but the items absorbing the radiation will remain heated. If you make the windows darker, the windows would absorb the heat instead of the seats/etc and re-radiate it both outside the car and a small amount in to the seats/dash as well, thus reducing the amount of radiation reaching the seats/items inside. The windows would transfer small amounts of heat to the air and the items in the car would transfer much less heat to the air than without dark windows (assuming the air temp outside and inside are relatively the same, the outside air would remain cooler if the interior air started heating up and heat loss to the outside air from the window would then be larger and be the more preferential heat transfer route neglecting fluid flow i.e. outside air = giant stagnant heat sink). So interior would heat up to a point until heat loss to outside air is preferentially easier or there's an equilibrium between heat loss to outside of car vs infrared absorption of seats/dash.

 

I've always had light colored vehicles for the radiation reflection reasoning, so the argument about the darker windows absorbing more heat makes sense. A clear IR filter/reflector would be nice to keep heat down. I've never had to actually sit down and think about this :headscratch: haha, but now I have the Bordeaux Reserve and want to use the A/C less to maximize my efficiency.

 

Edit: I neglected to include microwaves and radio waves as well as IR.

Edited May 23, 2013 by kuzzi

[acdii]

man, that made my head hurt! LOL IR does make more sense than UV(questioned that in my mind after posting too).

[kuzzi]

Check this out, blocked 97% of IR in the 900 to 1000nm spectrum (even though IR exists in 700-1000nm).

 

http://solutions.3m.com/wps/portal/3M/en_US/ScotchgardAutoProtection/Home/CarBuyers/Home/Products/WindowFilm/CrystallineWindowFilm/

[kuzzi]

Check this out, blocked 97% of IR in the 900 to 1000nm spectrum (even though IR exists in 700-1000nm).

 

http://solutions.3m.com/wps/portal/3M/en_US/ScotchgardAutoProtection/Home/CarBuyers/Home/Products/WindowFilm/CrystallineWindowFilm/

 

So this film blocks 32% of all IR. 3M has other films that block 40% of all* IR.

 

*They don't specifically state the wavelength, but I assume it is all IR.

[bcrisp]

So this film blocks 32% of all IR. 3M has other films that block 40% of all* IR.

 

*They don't specifically state the wavelength, but I assume it is all IR.

 

Kuzzi & acdii,

 

You may be interested in Prestige's Spectra PhotoSync nano tint product as well (http://www.prestige-films.com/auto_photosync.shtml). It purportedly rejects up to 98.5% of IR between 950nm - 2500 nm: http://www.prestige-films.com/docs/Photosync_DataSheet.pdf

[kuzzi]

 

Kuzzi & acdii,

 

You may be interested in Prestige's Spectra PhotoSync nano tint product as well (http://www.prestige-films.com/auto_photosync.shtml). It purportedly rejects up to 98.5% of IR between 950nm - 2500 nm: http://www.prestige-films.com/docs/Photosync_DataSheet.pdf

That still leaves 700nm-950nm unaccounted for. But I do not know how much heat it generated in that small spectrum. My guess it's that it doesn't generate much heat being so close to the visible light spectrum. Otherwise the color red would generate heat, and that would just be freaking weird, haha.

[acdii]

That still leaves 700nm-950nm unaccounted for. But I do not know how much heat it generated in that small spectrum. My guess it's that it doesn't generate much heat being so close to the visible light spectrum. Otherwise the color red would generate heat, and that would just be freaking weird, haha.

Why are heat lamps red then?

[Guardian_Bob]

That still leaves 700nm-950nm unaccounted for. But I do not know how much heat it generated in that small spectrum. My guess it's that it doesn't generate much heat being so close to the visible light spectrum. Otherwise the color red would generate heat, and that would just be freaking weird, haha.

 

 

So a couple of things, words like block and reject are marketing terms. You care about absorption and reflection. A material may "reject" a wavelength by absorbing it, and you're no better off (the material heats up and then radiates that energy out, right into your car).

 

3M specifically talks about reflecting; however, this is not quantified. I mean you don't really want to know what you're buying, right?

 

So a brief talk about wavelengths, energy and absorption.

Take a gamma ray. Lots of energy, very hard to produce. 100 keV. Can go through most thin materials without breaking a sweat. The wavelength is tiny. Smaller than an atom. In order to absorb such a wave, the energy of the wave must be completely transmitted to the object. Usually this translates into heat, by vibrating molecules. In some cases (especially with high energy waves) this will result in knocking an electron off, damaging DNA, etc. This is why sunscreen works on ultraviolet light. Damaged DNA leads to mutation which generally takes the form of cancer. Nasty stuff, wear your sunscreen people.

 

On the other side we have radio waves. (Sound waves are a result of compression of air, not strictly part of the EM spectrum.) Radio waves are long. Very long. The energy needed to create such waves can be as small as a 9 volt battery. (Actually smaller but you get the idea.)

 

So absorption of this energy doesn't result in much heat at all, which is good. Take for example 2.4 Ghz, water absorbs that range especially well. That said your WiFi router doesn't give you the equivalent of a sun burn. But in greater doses it can be used to heat food, in what's known commonly as a microwave. That's right kids, you want to know why your WiFi dies when you start making popcorn? The microwave floods the area with 2.4 GHz radiation and chokes out your signal.

 

So where does this leave us:

Small wavelengths = lots of energy

Long wavelengths = less energy

 

So it turns out that ultraviolet waves are shorter than visible waves (starting at violet going to red) and visible waves are shorter than infrared waves.

 

So which wavelengths would you like to reflect? Well if you're trying to prevent energy transfer (keep the inside cooler in the summer based on energy from the sun) the longer wavelengths are your friends and should be invited to the party while rejecting the shorter wavelengths.

 

Oh and don't be fooled, visible light does generate heat. Remember what you see is only the light that is reflected, not what is absorbed.

 

Okay so all this talk, but no conclusion. Well, remember your dash is mostly black, so any and all light energy coming through the front window will be absorbed and radiated. While tinting can help a little with this, the three biggest factors will be, the color of your car, can heat escape and if you can block all the energy.

 

So use a windshield screen, preferably in white or silver on your front window. That will work the best. Tinting at best will have a minor effect. We're talking .1 MPG, if that. Cracking your window so heat can escape would do more. Also white cars have much less heat gain, due to the reflection of all visible light.

 

TL;DR version:

No, tinting won't help your MPG in the summer. Have you considered cracking your windows?

Edited June 3, 2013 by Guardian_Bob

[hybridbear]

Thanks Guardian_Bob for the excellent explanation!