House Tau - John Dunn, Consultant, Ambertec, P.E., P.C.

Hurricane Sandy came through this area on October 29, 2012. We had some house damage. Although nowhere near what was being shown in the news, our electric power failed at 7:20 PM. Power stayed off for five days and was then restored, only to fail again on November 8th in the midst of Nor'easter Adele that brought a really heavy and wet snowfall. This second failure was repaired on November 9th at 10:37 AM. All in all, we came though things relatively unscathed.

I was up and awake when the second power failure occurred. It was 2:15 AM. I checked the house's hall thermostat and saw that the temperature reading was 68°F. I decided to record the temperature reading from time to time while the power was off. This was the result: 

I decided to fit an exponential equation to the data points using the method shown at the following URL:

http://licn.typepad.com/my_weblog/2010/11/fitting-exponential-equations-to-data-john-dunn-consultant-ambertec-pe-pc.html

I used the zero, 450 and 785 minute points and found an essentially exponential temperature decay versus time relationship with a thermal time constant, or tau, of 16.6 hours. I take that number to be the thermal time constant of the house.

This could be useful because we have two parakeets to consider, "Featherfoot" (left) and "Monet" (right). We're told that they need a room temperature no cooler than 50°F so now, when the next power blackout happens, I will have some idea of how much time I have before I will need to take these two birds somewhere else.

 

 

Comments

[Don Humphrey]

Hi John,
Don't take them into a Mine for protection.

[Gene]

Your result would differ for different outside temperatures and climates; i.e. the Tau would be shorter in Winter on a cloudy, rainy day than in Summer on a bright, sunny day. Also, you assumed a constant outside temperature when taking your data, and that was likely not the case from 2:15 am to 7:35 pm.

[John Dunn]

Actually, I didn't make any assumptions at all. I simply fit an exponential equation to the actual data and found it tracked rather well which surprised me a bit. That night and through the dawn and into the evening, the outside temperature fell a little, then rose a little after sunrise and then fell a little, but not by very much.

[Don Humphrey]

Wouldn't this data say something about
your home insulation. Looks good to me.