Saturday, July 19, 2008

How hot is it?

Last time you were in your neighborhood feed store (yes, we still have one here), you might have noticed a thing hanging on the wall that looked like the picture above, only much, much older.

What was probably being recorded were Heating Degree Days.

In the U.S., we usually use 65-degrees as the base temperature. The idea is that if it's 65 outside, you probably do not need to run your furnace or your air conditioner inside.

"Days" here does not mean actual days.

If it's 40-degrees outside than 65 - 40 = 25 Heating Degree Days (for today).

You do the same to calculate Cooling Degree Days.

Say it's 95 outside, then 95 - 65 = 30 Cooling Degree Days (for today).

Who cares?

Actually bunches of people. As Heating Degree Days increase, the demand for heating and natural gas increase. Forecasts of the number of Heating Degree Days in a Winter are used by your utility to figure how much energy it will have to supply to homes and businesses to keep warm. Forecasts are also used by commodity speculators trying to guess what the prices of energy will be next winter.

As Cooling Degree Days increase, the demand for electricity increases. Same deal, utilities use the forecast of Cooling Degree Days to estimate how much energy they will need to produce or buy during the air-conditioning season.

The Heating Degree Days devices used to be in feed stores so farmers could see when the sun was generating enough energy locally to grown certain crops. My impression is that the devices are still just in the old feed stores because they simply haven't been taken down. The local feed store still has its, I guess, because it is also a propane supplier.

Click HERE for a nifty site that will calculate a Heating Degree Days and Cooling Degree Days chart for your city. Remember, "Days" are not 24-hour periods but rather units of measurement. Below are some sample cities:

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