28 FEBRUARY 2003
DATA SET PAGE 13: BUILDING ENVELOPE LOADS. Figure 2-13 is an
example of Data Set Page 13. Data Set Page 13 consists of charts summarizing a site's
mean heating and cooling degree days.
Explanation of Charts
Calculation of Cooling Degree-Days. Cooling degree-days are derived by
multiplying the number of hours that the outdoor temperature is above the base
temperature of 65 F (18 C) times the number of degrees of that temperature
difference. For example, if 1 hour was observed at a temperature of 78 F, that
observation adds 13 degree-hours to the annual total. The sum of the degree-hours is
divided by 24 to yield degree-days.
Calculation of Heating Degree-Days Heating degree-days are calculated
similarly, against the base temperature of 65 F, so a 1-hour outside temperature
observation of 62 F adds 3 degree-hours to the annual total. Heating degree-days are
summed separately from the cooling degree-days. Heating and Cooling degree-hours
do not cancel each other out, since both heating and cooling conditions may occur over
the course of a given day.
Alternate Cooling Degree-Days Calculation. A separate file has been
added to the AFCCC W eb site to include the cooling degree-days based upon a base
temperature of 50 F. This file is located on the Engineering W eather Data page under
the Standard EW D Package file. This data is intended to allow selection of the proper
Building Envelope Requirements table from within ASHRAE/IESNA Standard 90.1 of
2001 for energy conservation design. The cooling degree-days based on 65 F
tabulated and graphed here are historically used to estimate loads as suggested in
paragraph 2-10.2 below.
Suggestions for Use. Degree-days are used to estimate the sensible heat
and sensible cooling loads on the building envelope. Degree-day loads can be used to
estimate the annual energy consumption of a building, provided that the loads from
ventilation and infiltration air are also considered (see paragraph 2-11).