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.
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:
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:
- Prius PV Cell Fan
- The effect of turning ON my battery charger controller using the PV cell.
- Sunshield
- 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:
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.
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.
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.
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.
