Article on cabin temperature (and traction battery temperature) when parked

Hypermiling in stop-n-go and slow-n-go rush hour city-suburb traffic takes about 20% to 50% longer than normal driving, so a normal 40 minute commute takes 60 minutes or more. The Prius (as well as most other vehicles) normally come standard with windows with about 15% tint which still exposes the driver (especially to the left side of the driver's face) to a great deal of skin damaging Ultraviolet rays. So I put on broad spectrum sunscreen to protect against this. I first noticed this phenomena about 15 years ago when I was commuting for +75 minutes to work from MD-VA (+32 miles one way) I noticed that the left side of my face getting more age spots than my right side - even when the windows were rolled up so I started wearing sunscreen for long commutes/trips (before I was even tried doing this hypermiling thingy). Dermatologist have a special term for this type of one side ultra violet ray sun damage - it is called... unilateral dermatoheliosis[1]. I found sunscreen with zinc oxide and titanium dioxide more effective than most - albeit it can make your face sort of whitenish - it is a drawback I'm comfortable with.

HTH
Walter Lee
aka "HyperDrive 1" on cleanmpg.com
2010 Toyota Prius III, Blue Ribbon, OE floormats
Yokohama Avid S33D

[1] two sources with the same study and photo.

Bill McElligott, Delivery Truck Driver, Has Severe Sun Damage On One Side Of His Face (PHOTO)

Trucker accumulates skin damage on left side of his face after 28 years on the road - HealthPop - CBS News

Thanks for the response.

According to this post 2010 Prius Window Specs | PriusChat, the front windows of a Prius filters 91% of the UV (SPF 11). Throw in some 99% UV cut tint films, you are only getting .09% of the UV. In SPF terms, it would be SPF 1,111. Better than any sunblock.
I am a cyclist and normally use SPF 50 when out training for 3-4 hrs at a time. No problems yet. Skin damage while driving is the least of my concern right now.

I think your hands take the brunt of sun exposure when driving. Most of the time I wear driving gloves. The wheel feels better even with my wheelskinz and the interior of the car stays cleaner. Its alot easier on your hands too.
All that white stuff you see on the dash is shedding skin from the steering wheel. The Gen II stock wheel with no cover I find to be extremely abrasive.

I think modern auto glass has better UVA protection than it used to? I'm guessing the truck driver in the pictures above drove most of those years with glass that had little or no UVA protection. But he's still an extreme case. I wonder if the table linked to above, which I've reproduced here, is still correct for MY 2012. I don't think the water repellent coating is still used.

It's interesting that there doesn't seem to be a lot of correlation between the tint and the UV cut rate. I assume that "UV cut rate" refers to UVA since glass already blocks UVB?

GLASS LOCATION	COLOR	GLASS TYPE	UV CUT RATE	SOLAR HEAT REDUCTION RATE	VISIBLE LIGHT TRANSMISSION RATE
Windshield	Green	Laminated (Sound Insulated)	100%	55%	80%
Sliding Moon Roof	Dark Gray	Tempered (UV Cut)	96%	23%	19%
Front Quarter	Green	Tempered (UV Cut)	92%	46%	74%
Front Door	Green	Tempered (UV Cut)	91%	49%	75%
Front Door (Prius IV and V)	Green	Tempered (Water Repellent Coated)	91%	49%	75%
Rear Door	Green	Tempered (UV Cut)	90%	51%	76%
Rear Quarter	Green	Tempered(UV Cut)	89%	47%	74%
Rear Hatch	Green	Tempered (UV Cut)	89%	47%	74%
Rear Hatch Lower	Dark Gray	Tempered	92%	32%	29%

FYI, auto glass blocks a large amount of UV light, especially in the spectrum that gives you sunburn (UVB). Tinting can provide a benefit in blocking UVA (which is still damaging, but won't give you sunburn), because many plastics inherently block UV, including the plastic used for the tint. (The plastic used to laminate the windshield blocks most UVA too, so you're already well-protected in the front.)

Here's an abstract of a study that measured UV transmission in some cars, and their conclusion:

Not to discourage a practice that I'm sure a dermatologist would be pleased with, of course. I've just never heard of somebody needing to use sunscreen while inside a car before.

Also the battery is about 70 lb, not 110.

Agreed

This is an incorrect way to look at it; the test is showing the rate of heat transfer through the tinting film and glass as compared to un-tinted glass. The tinting film slows the rate of transfer, both of incoming and out going heat energy. Thus the un-tinted glass allows the air behind it to heat up faster, but it also allows it to cool faster when sun exposure stops. The peak temps still wind up within a few degrees of each other, the laws of physics predict this, and the test confirms it.

This is the point, you want to eliminate as many variables as possible so you can create a direct comparison of the effect of the window tinting by itself.

Very interesting. Thanks for posting the link.

In what way do you find it incomplete? Their methodology looks quite thorough to me.

What difference does that make in this discussion? These tests were done to determine if the different heat blocking methods offered any real protection to humans and animals left in closed vehicles exposed to direct summer sun. The danger zone for human and animal life begins at roughly 40 degrees Celsius. These tests show that human and animal life is still exposed to dangerous air temps no matter what heat mitigation is applied. Actually this correlates well with the Prius because it is the cabin air temperature that threatens the “health” of the Traction Battery. The cabin air temperatures reached in all circumstances are still too hot for the HV battery without the immediate use of the cabin air-conditioner at startup.

Of course; the test used to show the difference between having the windows up and having them down 45mm. How is this incomplete, or jumping to conclusions? The tests would have been incomplete without it.

These tests were thorough and well done; and they show that the only real benefit of tinting and sun screens is to lower the possible surface temperatures of the seats and steering wheel. For some people, this is good enough to make their application worth the expense and effort, for some it won’t. In any case the need to run the cabin air-conditioner to protect the Traction Battery and the health and comfort of the cabin occupants remains, in a car exposed to the sun for any real length of time while parked. Actually the tinting may be counter productive in a situation where you can have the vehicle shaded at the end of the day before you enter it for the ride home.

The discussion of UV protection is not related to these tests, especially when protection can be applied to the person or persons in the car whether the car has tinting or not. This might actually be preferred as the person would be protected both in and out of the vehicle.

When parked next to each other under the sun, my 2005 Blue had roof temperature of ~80C while 2010 blizzard white was ~60C. Which paint/crearcoat will last longer?

- Alex

It's always good to double check the number ... sources need to be verified.
So I double checked my information with Toyotas Technical Information System at
TIS

and this is what officially Toyota numbers are:

The 2012 Prius c NiMH battery is 68 pounds [1]
The 2010-2012 Prius Hatchback NiMH battery is 90 pounds [2]
The 2012 Prius Plug Li-Ion Battery is 168 pounds [3]
The 2012 Prius V NiMH battery is 90 pounds [4]
The 2004-2009 Prius NiMH battery is 86 pounds [5]
The 2001-2003 Prius NiMH battery is 100 pounds [6]

Yep. I was wrong ... but you are too! RFLOL.
However, thank you for reminding me to double check my sources...
And this is always a good thing.
Humbling as it is for me - that's how I stay on track with the truth
regardless of how many wrong turns I make.

HTH
Walter Lee

[1] see page 14 of 33
https://techinfo.toyota.com/techInfoPortal/staticcontent/en/techinfo/html/prelogin/docs/priusc.pdf
[2] see page 15 of 38
https://techinfo.toyota.com/techInfoPortal/staticcontent/en/techinfo/html/prelogin/docs/3rdprius.pdf
[3] see page 44 of 74
https://techinfo.toyota.com/techInfoPortal/staticcontent/en/techinfo/html/prelogin/docs/priusphvdisman.pdf
[4] see page 15 to 34
https://techinfo.toyota.com/techInfoPortal/staticcontent/en/techinfo/html/prelogin/docs/priusv.pdf
[5] see page 15 of 26
https://techinfo.toyota.com/techInfoPortal/staticcontent/en/techinfo/html/prelogin/docs/2ndprius.pdf
[6] see page 16 of 33
https://techinfo.toyota.com/techInfoPortal/staticcontent/en/techinfo/html/prelogin/docs/1stprius.pdf

I know what I'm doing sounds awlfully odd to many - but it is working out for me.
I'm using Broad Spectrum UVA/UVB SPF 30+ when I'm out doors for any extended time frame.
When selecting a sunscreen I go by the amount of Zinc Oxide and Titanium Dioxide when selecting sunscreen.
Here is a list of ones I think are effective:

Blue Lizard : Baby SPF 30+ Titanium Oxide 5% Zinc Oxide 10%
Blue Lizard: Sensitive SPF 30+ Titanium Oxide 5% Zinc Oxide 10%
Neutrogena: Pure & Free Baby SPF 60+ Titaium Oxide 4.9% Zinc Oxide 4.7%
Johnson's baby daily face & body lotion SPf 40 Titanium oxide 12.2% Zinc Oxide 5%

Beyond the cosmetic issue, one side effect of putting on too much sunscreen is vitamin D deficiency - but this is manageable with supplements and dietary changes. The newer synthetic sunscreen have the advantage of being more transparent and less expensive but they degrade quicker (hence provide less protection) so they need to be reapply more often (which is not possible when I'm driving). Over the last two years, I was using the synthetic sunscreen (SPF +30 to +75) on my arms and was using the traditional Titanium oxide and zinc oxide sunscreens (listed above) on my face. Over that time, I saw my hands-arms tan slight darker than my face. While not a perfect test - this suggest to me that the Titanium oxide and zinc oxide sunscreens were more effective than the newer synthetic sunscreens.

Walter

From a fuel economy standpoint as well as long term health of the HV battery I would suggest NOT turning on the A/C immediately upon entering the car. The A/C system is woefully ineffective at removing so much heat for the first minute or two. The high load (1500-1800watts) may also raise battery temperature even higher than simply rolling down the windows and venting heated air for the first few minutes. We already know what the A/C will do to mpg in this situation.

Justin, do you have the graph I made of AC power consumption ? Looked to me like ventilation was equal to a 1500 watt AC draw for the better part of 15 minutes on a hot day starting from a baked car.

We must keep in mind that this study is represented in such a way so as to make it appear that sunshades, cracked windows and tinting are not very effective at controlling heat in the car but when added together there can be a substantial difference in interior heat. Of course we cannot change the laws of physics but we can reduce the impact of solar insulation by using various methods to reduce heat soak and it's negative effects on us, the car and our mpg. Also keep in mind that these measurements were in Celsius. Most of the differences they found we over 5 degrees F and some as high as 20 degrees F if I remember correctly. That is quite a bit of difference when you jump into a car!

Today it was 99F outside. My car sat in direct sunlight from 6am to 2pm. I jumped in the car after work (2pm) and I could barely discern a temp difference between outside temp and inside temp thanks to the sunshade (PriusChat Shop), window tinting, cracked windows and the solar roof. Had I parked in the shade it would have been even cooler.

I could fire up the old PC and get it. I didn't want to share it online until you were done with it and I had permission.

Please do. I did change the look of the graph in the google Doc, if you are inclined to use that instead.