degree days

[nh3simman]

After 20 years in the field of thermal engineering, I has asked for the first time yesterday to give the degree days.

Can someone give a simple definition?

Why is it useful?

When would you use it?

[NoNickName]

Have you tried either on wiki or on google by searching for "growing degree days" or "Allen method"

[Argus]

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In its simplest form, degree days are the aggregate of the maximum and minimum ambient temperatures in a particular location or area over a number of years.

Obviously there is far more to the application of degree day data than that and some very complicated computer models exist. They are extensively used in the UK in the analysis and prediction of building carbon efficiencies and in carbon reduction technologies.

To work effectively they need the careful collation of climate trends over many years. The UK bench mark is 20 years, though data goes back much further than that, hence it is not something you can pluck out of the air, so to speak, without the benefit of supporting weather trends in the area for some considerable time and the ability to interpret the information.

If you search the internet there is a lot of technical detail out there.

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[Abby Normal]

The degree days are often used to estimate energy usage, they are proportional to the amount of heat needed for a heating season. There are also cooling degree days as well.

A degree day muiltplies out similar to kilowatt hours.

A heating degree day could be based on an 18C ambient in metric.

If the average outdoor temperature was 17C over a 24 hour period, then it was one degree lower than the base temperature of 18C for one day, it would have the value of one degree day.

If the outdoor average was 8C for a 24 hour period, then it would be 10 degrees below the base line for an entire day and it would represent 10 degree days.

If the outdoor average was -22C for a 24 hour period then it was on average 18-(-22)= 40 degrees below the base line for a day, so that would represent 40 degree days, based on 18C.

In Canada, a heating season could tally up 6000 or more such degree days in a heating season. The amount of fuel needed to keep warm is proportional to the number of degree days.