Passage III

Heating degree-days (HDD) and cooling degree-days (CDD) are used to estimate the amount of energy needed to heat or cool, respectively, any building on a given day. HDD are calculated by subtracting the daily mean temperature (Td) from a base temperature of 65°F. Each degree difference is one HDD. CDD are calculated by subtracting 65°F from Td.

Table 1 lists, for each of 10 US cities, the latitude of the city and the city's total HDD and CDD for a 1 yr period.

For the state of Illinois, the annual total HDD and the annual total CDD were determined for each of the years 1985-2010 (see Figure 1).

20. Consider the HDD equation and the HDD trend line shown in Figure 1. The slope of that trend line is nega­tive, which indicates that over the 26 yr period, the average value of Td:

Answer and Explanation

Your Answer is

Correct Answer is G

Explanation

You can answer directly based on common sense, or: HDD=65ºF-T (T<65ºF), HDD is getting smaller and smaller, indicating that the number of days when the temperature is below 65 degrees Fahrenheit is getting fewer and fewer, and the temperature is rising.