7.3: Residential Heat Loss (III)

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Seasonal Heating Degree Days

In the previous section, we are assuming that the outside temperature remains the same for all 150 heating days in a season. This is not realistic, but it explains the method to calculate the HDD. In a more realistic example we need to find the temperature difference for each day and add all the temperature differences.

We will now look at Seasonal Heating Degree Days (HDD), which is the sum of temperature differences of ALL days - rather than just 1 day or 1 week - during which heating is required.

Table 7.3.1 provides Seasonal HDDs for selected places in the U.S. The higher HDD indicates a higher heat loss and therefore, higher fuel requirements.

HDDs are used to estimate the amount of energy required for residential space heating during a cool season, and the data are published in local newspapers or on the National Weather Service website.

Table 7.3.1. Annual degree days for selected places

Place	Degree Days
Birmingham, AL	2,823
Anchorage, AK	10,470
Barrow, AK	19,893
Tucson, AZ	1,578
Miami, FL	155
Pittsburgh, PA	5,829
State College, PA	6,345

Source: NOAA

Calculating Seasonal HDD

To calculate seasonal HDDs, use the equation

\[ Seasonal \, HDD = ((T_b - T_a) * (\# \, days \, in \, month \, 1)) + ((T_b - T_a) * (\# \, days \, in \, month \, 2)) + ((T_b - T_a) * (\# \, days \, in \, month \, 3)) \]

Remember, in months where the average temperature is equal to or greater than 65, there will be no heating degree days, so the value for the month will be 0.

Example Problems

Example 1

Given the following set of average temperatures, by month, for State College, PA, calculate the HDD for the heating season.

Jan.	Feb.	Mar.	Apr.	May	Jun.	Jul.	Aug.	Sep.	Oct.	Nov.	Dec.
25°F	28°F	37°F	48°F	59°F	67°F	71°F	70°F	62°F	51°F	41°F	31°F


Answer: The following video goes over the solution.

Example 2

If Ms. S. Belle moves from Birmingham, AL (HDD = 2,800) to State College, PA (HDD = 6,000) how much can she expect her heating bill to increase?

Answer: The following video goes over the solution.