My contribution to reduce global warming

Another experiment I performed was about the exterior paint of the car. My Prius is dark gray so it is on the spectrum that absorbs most of the sun, having a scorching outside surface. It may not affect greatly the temperature inside the car but certainly increase the temperature of the air surrounding the car. I bought a thermal camera that is attached to an android cellphone (Seek) and that helped me understand better about the color of the cars and the temperature on them: it is incredible how the black cars can reach so high temperature compared with cars with white or light gray colors. 

 

But also colors like red gets really hot.   Well, painting my car to white is a very expensive option, so first I bought a couple of plastidip cans, and painted the hood on white, and then added some Jedi symbols on it with vinyl cut with my wife’s cricut. There was really a difference on the temperature of the hood compared with the surroundings. The downside of it was that the surface looks rough, I mean, I am not a professional painter and using a can to paint the hood is not as simple as you can think of.

 I ripped the plastidip and paint it again with it trying to be more careful, but still I was not totally OK with the results. So I kept it that way until winter when there is no longer need to keep the surrounding of the car cool.   

Before the next heat season, I brainstormed other ways to keep the outside of the car cool, and I hoped I could chrome my car. But thinking about the chroming process, it looked as an impossible idea. Then our friend Google images let me discover that you can actually chrome your car using vinyl! In fact, some guys chrome the complete car that way. But for my budget it would be too much money for my experiment.  I calculate if I take it to a shop they will cost around 500 dollars to, so I looked on amazon and eBay and I could get the vinyl, on several colors also. I bought a 10 dollar sample, just enough to cover the “black” spoiler of my Prius.

 I got the gold color because I thought it will combine with the silver/chrome if I decided to go this way. I discovered that applying the vinyl is not like covering the books when you were at school; it is a little bit trickier. But well, it was just the first trial and it looked good, the only back draws is that after a couple of months it started to discolored a little bit.  But well, I bought the cheapest vinyl as possible, not the 3M that can last more. So with that practice I purchase now the chrome/silver vinyl and installed it on the top flat surfaces of the car which are the ones that gets most of the sun. I really liked the look, half up of the car was reflecting the sky, the blue with the clouds, and it looks really nice.

 Measuring the temperature of the metal, it was a very big drop compared with the original dark gray areas. 

  Also measured the sun shade, and it was so much cooler.

They said that the cheaper is sometimes expensive; I installed them on April, and since July I started to see some degradation on the silver chrome: first on the sunroof it started with black dots that started to grow, then I tried to take off some portions of the frame of the window and it leaved shiny residues that will require me to use a heat gun to take them off.  Then on the Hood I just started to see the black spots I originally saw on the moon roof. I will wait until fall or winter to take it off, hopefully without damaging the paint of my car. But I may consider buying this time the 3M vinyl, hopefully it is not that expensive as the $80 dollars that the cheap vinyl cost me.

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.

Design of experiment: Does it really help to have the solar fan to reduce the heat accumulation on your car?

After having installed a solar charge controller on my Prius with solar roof, I was concerned if the performance of fan to decrease the trapped heat inside the car will be reduced. The only way I can do that is by monitoring the temperature inside of the Prius using the vent with and without the charge controller activated. So I looked for some cheap temperature logger and found this on eBay from a Chinese vendor:

I paid ~$30usd for it with free shipping, so after looking to different options available, I liked this because the high ranges of temperature it can measure. I can just program the frequency to record data, it can record Temperature, Relative Humidity and dew point. It took a month to arrive but it will give a chance to the winter to end so that I can use it under more warm and sunny conditions.

When I finally have it in my hands, I decided that it would be a good idea to check how accurate it is to measure the temperature... when connected by the USB on my computer, the software the comes with it showed approximately the same reading from my infrared thermometer and from another desk thermometer I have.   Good! enough... but how good is to detect changes on the temperature overtime?   Well I leave it on my porch for 2 days taking readings, and then I compared it with data downloaded from Weather Underground.

Blue line are the readings from my temperature logger, and green line is from Weather Underground historic data for those days. Just ignore the other lines since they are humidity. Also be aware that I am using Celcius, so no, those are not freezing temperatures.

The pattern is very similar but as you can notice from the second day there is an out of phase on the data for more than an hour! I am not worry about the magnitude changes since there are factors that can change the readings for a couple of degrees since underground weather stations are not exactly on the same place as my sensor, and may be the sun on my porch can increase the readings on my logger.

I checked again the logger view of data with the software and noticed that the clock of the logger is not synchronized with the computer. Well, that's what I get with cheap Chinese items. I sent an e-mail to the eBay vendor, and also to the manufacturer to see if they are aware of the problem and it is possible that it can be fixed with some firmware update, however I never received a response from them. But anyway, this is not going to stop me. I can still calculate a "factor" to adjust the time registered for each reading assuming the out of phase is linear. And I am going to have the logger to work only around 8 hours recording data every 5 minutes. Doing this way, every day I planned to take measurements first step will be to sync the clock of the logger, and a the end of the day I will stop the recording, then record how much time is out of phase and then obtain a factor to adjust for every 5 minutes of increments. Sounds complicated right? But thanks to Google sheets, which is the free excel from Google, I can easily adjust the time recorded for each of my logger readings.

Look at the following chart, this time the lines of the temp readings from my logger match better the readings from weather underground.

Now that I have a temperature logger data that I can trust I can start my Design of Experiment. A design of experiments is basically an statistical tool to investigate how certain variables can affect to the results that we want. My objective is to reduce the interior temperature on my Prius, but it can be also to reduce the difference between outside temperature and inside temperature. The variables I used to plan my experiment were:

1. Prius PV Cell Fan
2. The effect of turning ON my battery charger controller using the PV cell. 
3. Sunshield
4. Slightly open the moon roof to let hot air escape from inside the car.(3 fingers)

They looked like few variables so I decided to do the full experiment, which is basically all the possible combinations. Then I have to do the the experiment on 16 days, that is one combination per day.
I performed the different trials when parking my car at work, trying to avoid any other variables, i parked always with my windshield pointing to the west so the full sun of the afternoon can enter to the car. Also as a reference, all the morning the car receives shade since there is a wall from the building on the east of the parking lot so there was not a significant increase of the trapped heat in the morning.

The following table is an example of the experiment and the different combinations to evaluate:

RunOrder	Fan	Charging Controller	Moon Roof	Sunshade	Highest Temperature Difference	Inside Temperature when driving back home
1	1	1	-1	1	12.3	47.3
2	1	-1	1	1	10.2	44.4
3	1	1	-1	-1	17.9	51.7
4	-1	1	1	-1	16.5	50.5
5	-1	1	1	1	10.2	44.8
6	1	-1	1	-1	15.5	54.1
7	-1	-1	-1	1	11.3	47.2
8	-1	1	-1	-1	14.6	47.6
9	1	-1	-1	-1	15.6	49
10	-1	-1	1	-1	15	50.7
11	-1	1	-1	1	9	45.1
12	1	1	1	-1	15	52.8
13	1	1	1	1	12.2	48.4
14	1	-1	-1	1	9.8	45.9
15	-1	-1	1	1	8.1	45.3
16	-1	-1	-1	-1	15	56.7

 1   Turned on, or open moon roof
-1   Turned off, or closed moon roof.
Yellow, Red, Pink and cream colors are used to identify trials where the results should not be different because having the charging controller on when the fan is off, should not be very different since the charging controller does not cool down the car.
The green on the results section is to identify the days that were completely without clouds. A variable difficult to control on the experiment is the sun, since most of the days were partially clouded. Because of that I planned another experiment including Sunny/partial cloudy days as a variable. However that DOE I decided to use half factorial, otherwise I will have to spent 32 days taking data under the conditions I need. Half factorial DOE still give us a very powerful analysis without having to perform all the combinations trials.

RunOrder	Sunny/Clouds	Fan	Charging Controller	Moon Roof	Sunshade	Highest Temperature Difference
1	Sunny	FanOn	on	Open	On	12.2
2	Sunny	FanOff	off	Closed	Off	18.6
3	Cloudy	FanOff	on	Open	On	10.2
4	Cloudy	FanOn	off	Open	On	10.2
5	Sunny	FanOff	on	Closed	On	11.2
6	Sunny	FanOn	on	Closed	Off	15.8
7	Sunny	FanOff	off	Open	On	8.1
8	Sunny	FanOn	off	Open	Off	15.5
9	Sunny	FanOff	on	Open	Off	15.5
10	Cloudy	FanOff	off	Closed	On	12.3
11	Cloudy	FanOff	on	Closed	Off	13.7
12	Cloudy	FanOff	off	Open	Off	15
13	Cloudy	FanOn	on	Closed	On	12.3
14	Cloudy	FanOn	on	Open	Off	11
15	Cloudy	FanOn	off	Closed	Off	15.6
16	Sunny	FanOn	off	Closed	On	12.2

This time I placed the real condition on Minitab instead of the 1 or -1 that are as default.
If I was considering the lowest difference in external and internal temperature, the variable that most effect have on that is the sunshade. However, if I just consider the inside temperature at 5pm when I have to get inside the car, having a cloudy day or having the sunshade on are the variables have a strong effect.

To create the smaller difference of temperature outside/inside, then it needs to be Sunny, fan off, charging controller off, open moon roof, and sunshade installed. This is tricky because normally outside temperature will be lower than inside, so my goal is to have the inside temperature more near to outside.

For my goal to have a lower temperature inside my car when leaving work at 5pm the "optimal" combination based on the optimization plot from minitab is to be on a cloudy day, have the vent turned On, have the Charging controller off, the moon roof slightly open, and very important to have the SunShade blocking the Sun that heats the black dashboard of my Prius.

What about having the charging cell on or off? Does it affect the vent performance?

Based on these graphs, the steep angle lines are the ones with most effect, and as you can see fan and charging cell are almost flat, meaning they have not of a significant effect for my overall goal.

If you want to reduce the heat trapped inside your car, the solar cell vent is a really expensive option to have and the effect you will see to reduce internal temp does not worth the money. The most cheaper option and more effective will be the sunshade, but just don't buy those cheaper small ones, try to get those that fits better and covers most of the windshield in order to be more effective.