Degree Days: Heating And Cooling Contractors Use Them, And So Can You
Degree days refers to the number of degrees in one day that the average outdoor temperature is above or below a set reference temperature. The reference temperature represents the most desirable indoor air temperature for human comfort. And the most commonly used reference temperature in degree-day calculations is 65 degrees.
The difference between the average outdoor temperature and the desired indoor temperature for any given day equals the number of degrees an air-conditioning or heating system must condition the air. You can use degree days to determine Cooling Degree Days (CDD) and Heating Degree Days (HDD).
To find CDD, if the average temperature for a warm summer day in Wilmington, Del. is 80 degrees, and the reference temperature inside is a cool 65 degrees, then this particular day requires the cooling system to cool the outside air temperature down 15 degrees. Therefore, the CDD is 15. If every day during one week has an average temperature of 80, then the degree days for that week would be 105, or 15 multiplied by 7. In this way, you can calculate the amount of degrees your cooling system has to work for an entire season.
To find Heating Degree Days (HDD), calculate one day’s average temperature, for example, 35 degrees, and subtract the average from the reference: 65 subtracted by 35 is 30 HDD. You can calculate the HDD over an entire season using this knowledge.
Wilmington, Delaware, for example, has an average of 1,630 cooling degree days and 4,999 heating degree days per year. It’s easy to see from these numbers that the heating system has to work a lot harder than the air conditioner in this particular climate. Having energy-saving products installed in your home, such as an efficient heating system and insulation, means your heater doesn’t have to work as hard, and thus uses less energy, to keep that indoor temperature a comfortable 65. You can also use degree days to compare the efficiency of your systems over several seasons.
If you would like more information regarding high-efficiency heating and cooling equipment and how it can benefit your home comfort year ’round, please contact Sobieski Services today.
Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems).
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