What is the best time to close your blinds? Temperature logging with Arduino (Part 2)
Over the last three weeks or so, I have been recording the temperature inside and outside my room to see when the best time to close my blinds is, in an attempt to keep my room warm. Part 1 details the equipment used to record the temperature, and this second part is going to detail the data analysis.
If you are here simply to find out the best time to shut your blinds, this blog post is going to be a disappointment, as I don’t reach a strong conclusion. In saying this, lets have a look at the data and see what we can conclude from it.
Firstly, the sample size is far smaller than I would have liked. Between work, life, and the weather, I didn’t get as many samples as I was aiming for. I often found myself away from home in the early afternoon, inhibiting my ability to close the blinds between 12:00 – 16:00 (my housemates were not home either). I had to move out of my room earlier than planned (new housemate was moving in, and I had to relocate to another room in the house which was north facing), and with the weather being as variable as it is, getting days with a similar external temperature profile, and with the blinds being shut at the correct time was a challenge. So with this limiting the recordings I was able to take, I have selected eight days which best represent the data I was attempting to record. With all of this in mind, and considering that the extent of my data analysis was staring at the data in various forms for half an hour, let’s get into it.
I figured the best way of seeing how warm it stayed inside with respect to outside, was to plot the difference in temperatures (difference = inside – outside), with the more positive the value, the warmer (i.e. better) it was. This is shown in the above plots, and as you can probably determine by observation, there seems to be no correlation between the time the blinds are shut and how warm it is inside.
The above table shows the external and internal minimums, along with the maximum difference between the two temperatures. One thing that I noticed whilst I was compiling the table was that the external temperature profile was inconsistent on a day to day basis, even when it reached a similar low temperature outside. With this in mind, I selected the four days with the most similar external temperature profiles, and compiled them into a table as shown below.
As the table shows, three of the days reached minimum external temperatures of -3.5oC ± 0.5o, with the minimum for the fourth entry being at -1.5oC. Looking closer at the plots with respect to time (at top of page), it can be seen that the external and internal temperatures intersect at around 16:00. This also coincides with the best time to shut the blinds to keep the room warm, as shown in the above table. This seems to make sense, as closing the blinds at the latest time that you can whilst the room is still warming up will allow for the most heat to enter the room, whilst leaving it any later will allow for that heat to be lost outside.
This explanation, combined with the (limited) data recorded, would suggest that the optimal time to close my blinds would be when the internal temperature equals the external temperature, which occurs at around 16:00 for my room. However, due to the lack of data points, and the large variations in the temperaure recordings as a result of the varying weather conditions, I cannot be too sure of this conclusion. In the best case scenario, closing my blinds at 16:00 would result in my room being 2oC warmer than closing it an hour later at 17:00. This result was underwhelming, as I was expecting to see at least a 5oC between the best and worst cases. To see if having the blinds shut actually made a difference, I left them up overnight, however the minimum temperature of that night was only -1oC, and the difference between external and internal was 7oC, and as such no conclusions can be made. I would however assume the blinds make a non insignificant difference, as anecdotally it is noticeably colder in my room when the blinds are left open compared to when they are shut.
So in conclusion, it appears that closing your blinds when the external and internal temperatures are equal is the best time, and in my case that is at 16:00. In the best case scenario, this should result in the internal temperature being up to 2oC higher than if the blinds were shut an hour later. If the blinds are left open constantly, you can assume you are in for a cold night. Even though it does not make a major difference, if I’m heading out in the afternoon, and won’t be back until the sun has/is going down, I think I will make an effort to close my blinds earlier, so that my room stays a bit warmer, and the cold winter nights are made slightly more bearable.
I’d be interested to see if anyone has done anything similar, even if it is anecdotally. If you have, or have any comments on this post, please let me know in the comments below.