Thursday, September 6, 2018

Preventing heat absorption in my Prius

Sun, heat and it consequences are always on my mind here on south Texas where you have high temperatures and high humidity therefore high heat index.  The last project I shared here was how to make my Prius more comfortable when riding back home from work. I tested the solar roof vented effectivity which resulted a very expensive option when bought my car and that a cheaper windshield sun shade would work better.  I made my own buying reflective Mylar and some corrugated carton which prove to be good but difficult to store inside the car, at least it lasted a couple of years. Later I have an idea to take the sunshade out of the car, so that the heat absorbed by it will be dissipated outside and not trapped inside.  Using the same reflective Mylar I bought before I cut it to the size of the windshield, and added some strong neodymium magnets so that it can be maintained in place. It worked great, except when there was some high winds which sometimes unsticked the magnet and have it hitting my glass. Thinking, millions of brains may have better ideas, I checked on Alieexpress  (Chinese version of amazon, where it takes like a month to receive your purchases from China), and found that they already had a similar idea: A reflective cloth on one side, and a soft cloth to prevent scratches or rubbing with the car body, and instead of my magnets they made some longer ears that you insert on driver and passenger doors just before closing them. 

I tested it for a year, but unfortunately the reflective cloth started to degrade and suddenly I got glitters inside my car. 

Next year I bought it from a different brand, this time it looked better, stiffer, and the side pointing to the car was black preventing any reflection of the internal heat. Unfortunately the degradation of the shiny side started after a few months too.
Placing the sunshade on and off takes time, practice until you dominate it, but it is not convenient. Thinking that the main source of heat for the car is the black dash absorbing the sun energy I considered those “carpet” like mats that you place over your dashboard. Knowing already that black colors absorb more energy than whitish colors I discarded those dark mats, but I was worried about the glaring that will come from it.  Finally I decided for a light gray mat, and as thought the glare is really annoying because it is reflected on your windshield to you so it is not good for your eyes. Fortunately I have polarized eye glasses that almost eliminated the glare, so with them it is more comfortable. 

From my previous experiments I decided that the interior temperature when entering the car when leaving work is the best variable to measure, so instead of having the temperature recorder all day I just bought a small thermometer that I installed in my dash on the area that the sun does not touch it. 

Does not require battery so it is convenient.  Coming back to the mat, I checked no significant improvement on temperature having the sun shade and the mat, but having only the mat it was like 5 or less degrees Celsius hotter than with the sun shade on. It is not that bad, considering that the sunshade alone reduces around 20C, so I can estimate the mat reduced 15C.

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