## Friday, November 5, 2010

### Is a ‘mean temperature’ just bad tempered?

No, actually the word is a meteorological term that refers to the averaging of two or more temperatures. In many cases, it is the result of taking the high and low temperature that occur over a twenty four hour period. It’s an important number for anyone who wants to get a feel for how warm or cold a day was ‘on average’ The term is also used quite often in figuring how many heating or cooling degree days were needed to heat or cool a home or business. One popular approximation method to get this number is to take the average or mean temperature on any given day, and subtract it from the base temperature of 65F. If the value is less than or equal to zero, that day has zero HDD. But if the value is positive, that number represents the number of HDD on that day. Here’s an example:

Let’s assume the high for the day at your location was 54 Fahrenheit and the low was 32F. The average therefore would be (52+32)/2 = 43. We then subtract this from the bas temperature (65) to get a twenty-two degrees. Therefore there were 22 heating degree days (HDD) for that period of time.  Now that I’ve confused you completely, you might want to go to this article on degree days for a good explanation. A wonderful calculation for figuring your degree days for the year is here.

In my research on heating my home for this winter, I’ve developed a rough approximation of how hard my furnace will have to work for the next day by just looking at the mean temperature that is expected. How I arrived at this will be the subject of a future blog.