Degree Days

Heating Degree days (HDD) are a general indicator of household energy consumption for space heating. Cooling Degree Days (CDD) are an indicator of energy consumption for air conditioning/cooling. Simply put, these indicators allow energy professionals to estimate/anticipate for energy demand!

How the Weatherbit API calculates degree days

Our API calculates Heating Degree Days/Cooling Degree Days on an hourly basis. Taking into account each hour's temperature compared to the baseline (threshold) given. This method provides for the most accurate degree day calculation possible.

Why hourly historical temperature data matters

The simplest method for calculating degree days is done by simply using the Daily Mean Temperature Method:

Heating Degree Days (HDD) = (65F - ((max + min) / 2))

This method is a bad approximation on all accounts, as it assumes that the daytime maximum temperature "cancels out" the daytime minimum temperature.

Suppose that the daytime's maximum temperature is 80F, and the minimum temperature was 50F. According to the industry standard approximation the total number of heating degree days would be (assuming a 65F threshold):

HDD = (65F - ((80F + 50F) / 2)) = 0

Seem's odd doesn't it? This calculation suggests that there was NO heating demand on this day. Now, let's suppose the hourly temperature data for this day was:

Time - Temp - (Temperature - 65F)
1am  - 55F (-10)
2am  - 54F (-11)
3am  - 53F (-12)
4am  - 52F (-13)
5am  - 52F (-13)
6am  - 50F (-15)
7am  - 52F (-13)
8am  - 55F (-10)
9am  - 60F (-5)
10am - 65F (+0)
11am - 70F (+5)
Noon - 74F (+9)
1pm  - 78F (+13)
2pm  - 80F (+15)
3pm  - 80F (+15)
4pm  - 78F (+13)
5pm  - 72F (+7)
6pm  - 68F (+3)
7pm  - 65F (+0)
8pm  - 62F (-3)
9pm  - 60F (-5)
10pm - 60F (-5)
11pm - 58F (-7)
12am - 55F (-10)

HDD = (Sum of degree-hours exceeding 65F) / (24 hours)

CDD = (Sum of degree-hours below 65F) / (24 hours)

HDD = 3.33 degree days
CDD = 5.29 degree days

As you can see, by using hourly historical weather data we arrive at a calculation of 3.33 heating degree days, and 5.29 cooling degree days! Where as using daily max/min, and averaging gave us an estimated  zero heating degree days, and zero cooling degree days!

Conclusion

Our API allows for retrieval of the most accurate heating or cooling degree day calculation possible. Our Historical degree day data can be retrieved by using our Energy Weather API. This API is available to all of our premium API subscribers.

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