Green on Green Crime: Energy Efficient Windows Melt Toyota Prius
January 26, 2012 11:47 AM
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National Association of Home Builders has promised an investigation into heat-glare from window treatments
Heather Patron of Studio City (Los Angeles, Calif.)
her neighbors of a dastardly crime -- melting her Toyota Motor Comp. (
. No, really. This was no Hawaiian Baby Woodrose-induced optical illusion, her neighbors’ energy-efficient window treatment had melted the plastic molding of her Prius' mirror housings.
Los Angeles is a seasonable southern city on the west coast. Its average monthly maximum temperatures are historically confined to the 64-77 ºF range year round [
]. Unsurprisingly, the big concern for residents in terms of energy efficiency is the cost of air conditioning. One of the major sources of heat entering the house is through window light. So southern Californians, like residents of other longitudinally southern U.S. states, have taken to applying reflective windows treatments, both as a cost-saving measure and as a "green" energy saver.
But in this case the approach backfired, as the neighbors' energy efficient reflective gloss created a brilliant beam during daytime hours that directed itself directly at the car port.
"The side view mirrors were melting. Anything that was plastic on the car was melting," the Prius-owner recalls.
Ms. Patron shows offer her damaged Prius. She claims her neighbor's energy-efficient window treatment did the damage. [Image Source: CBS]
And Ms. Patron says her Prius wasn't the only ones damaged -- a neighboring vehicle saw similar melting. She comments, "I'm positive that this window is what is causing the damage to my car. I just don't feel like it’s fair. I feel like it needs to be known that this is happening. And a lot of people probably have damage out there, that they aren't aware that it’s the windows that are causing this."
She claims to have measured the temperature in the car port when it's exposed to the beam and found it to be 120 ºF.
The damage occurred in Studio City, a suburb of southern California's biggest city, Los Angeles. [Image Source: Google Maps]
Similar claims of reflective windows burning people or plastics were
leveled in Sept. 2010 by a lawyer staying at the Vdara hotel
in Las Vegas, Nevada. Reportedly in that case the situation was even more severe as the reflective windows were acting as a hyperbolic solar dish, focusing sunlight into a "death ray", which swept across the pool deck.
Reportedly other homeowners have also complained about plastic-melting reflective beams coming off windows with certain energy-efficient treatments. The
National Association of Home Builders
has promised a thorough investigation into this problem.
What makes Ms. Patron's story more curious is that automotive mirror housings are usually primarily composed of ABS (acrylonitrile butadiene styrene) [
] -- the same type of plastic found in LEGO blocks and plastic pipes. Pure ABS has a melting point of 221 ºF [
], so it's unclear how the beam was able to melt the plastic, even if the air temperature was 120 ºF.
One possibility was that the black mirror plastic absorbed the light, and heated up to a temperature far hotter than the surrounding air (think of an Easy-Bake oven).
The Prius is the best-selling hybrid electric vehicle in the U.S. (and in the world).
[Image Source: Jason Mick/DailyTech]
The Prius is the best-selling hybrid electric vehicle in the world. As of March 2011,
3 million Prius vehicles had been sold
worldwide, with 1 million sold in the U.S. alone by April 2011.
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1/26/2012 1:22:39 PM
The open carport receives enough radiant heat to raise the air from 77 to 120 degrees? Peak solar about 1kw per meter sq. So 1KW direct from sun and assume 1kw for reflection. With 120 degree ambient. So at what point does the black body mirror housing obtain convective heat balance with the incident radiation of 2kw/meter? Yep about 200C, good melting point for most PVC's
1/26/2012 5:02:38 PM
Your figure is way too lax.
The black body mirror cannot have 1kw per sq. meter surface area, that's a huge mirror housing.
More like 250cm^2= 0.025m^2.
Reflection is not 100% efficient either, I'd say 90% since you are assuming a 1sq. meter window project all it's reflection on the mirror with no missed beam.
So the radiation input is 0.925kW
1/26/2012 5:53:37 PM
Yep the 2KW / meter sq. is general, but is the rate that a surface receives heat, regardless of the surface area (assuming no lens or focusing effect). This basically cancels area out of this, "back of the envelope" type "is it possible," calculation. Area cancels because convective heat transfer (cooling) very proportional to surface area, as is heating (the area exposed to the radiation (light)).
To be more accurate looks like 85% of infrared ration is reflected for the below film:
PVC melts from 100-260C
So 1.85KW/meter sq. is still enough to melt some PVC. (1kw from sun, .85 from reflection)
Solar Absorption for black paint is 0.98 (white is like 0.25)
From this we can see that if painted white it wouldn't hit over 100C...at least on the back of the envelope.
From the pic, looks like the convective currents (at the more vertical parts) get cooled enough. Its just the top has a slower moving air currents and then heats up, then melts.
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