Data: Heating & Cooling Degree-Days
Although degree-days are most commonly used
in agriculture, they are also useful in building design
and construction, and in fuel use evaluation.
The construction industry uses heating degree-days
to calculate the amount of heat necessary
to keep a building, be it a house or a skyscraper,
comfortable for occupation. Likewise, cooling
degree-days are used to estimate the amount
of heat that must be removed (through air-conditioning)
to keep a structure comfortable. Just like
growing degree-days, heating and cooling
degree-days are based on departures from
a base temperature. 65º F is almost always
used as this base. It is assumed for heating
load calculations that the occupants, lighting,
equipment, appliances, cooking, bathing and
other activities will raise the temperature
from 65º to 68º.
One heating degree–day is the amount of heat
required to keep a structure at 65ºF when
the outside temperature remains one degree
below the 65ºF threshold for 24 hours. One
heating degree–day is also the amount of
heat required to keep that structure at 65ºF
when the temperature remains 24ºF below that
65º threshold for 1 hour.
Likewise, one cooling degree–day is the amount
of cooling required to keep a structure at
65ºF when the outside temperature remains
one degree above the 65ºF threshold for 24
hours. One cooling degree–day is also the
amount of cooling required to keep that structure
at 65ºF when the temperature remains 24ºF
above that 65º threshold for 1 hour.
Depending on the calculation method, both
heating and cooling degree-days can accumulate
in the same day. Also, note that there are
no negative degree-days. If the temperature
remains below the threshold, there is no
degree-day accumulation.
Heating and Cooling degree-days may be calculated
by either the High/Low method or the Integration
method.
High / Low method:
In the high/low method, the software uses
the highest temperature and the lowest temperature
for a given day to calculate the average
temperature for that day. The difference
between the average temperature and the base
threshold are assumed to be the number of
degree-days accumulated on that day. For
example, if the average of the highest and
lowest temperatures is 24º below the base
threshold, the software assumes 24 heating degree–days
for the entire day.
Integration method:
In the integration method, the software calculates
degree–days using the average temperature
for an interval and the interval time. For
example, if the average temperature during
a 15 minute interval was 24º below the base
threshold, the software would calculate 0.25 heating
degree-days during that interval (24 * 15
minutes in interval/1440 minutes per day).
The number of degree-days during each interval
are added together to arrive at a degree-day
total. This method calculates degree-day
totals more accurately than the high/low
method.
The West Juneau Weather Station uses the
Integration method; except that for data
prior to November 2002, the High/Low method
is used.
Below are some representative heating and
cooling degree-day totals from different
parts of the United States.
Table data source: Williams, Jack. 1995.
The USA TODAY Weather Almanac and the West
Juneau Weather Station.
Source: Davis Instruments with modifications and additions by David Kent
SITEMAP | HOME | CONTACT | CURRENT WEATHER | GRAPHS & MONTHLY/YEARLY HIGHS & LOWS | ARCHIVES/RAIN DATA