SAMPLE (GIF 56kb)
Base temperatures for daily values are 15.0, 15.5, 17.0, 18.0
and 18.5 ° C
- Degree days give a measure of the effect of the seasons'
temperatures on crop growth and fuel requirements, especially
in the case of a building which is continually heated.
For each day that the average temperature is one degree
above the base temperature, one degree day has accumulated.
- Probably the most widespread application of the degree
day concept is the management of industrial and domestic
heating. Heating degree days are indicators of household
energy consumption for space heating. The air temperature
in a building is on average 2° C to 3° C higher
than that of the air outside. A temperature of 18° C
indoors corresponds to an outside temperature of about
15.5° C. If the air temperature outside is below 15.5° C
, then heating is required to maintain a temperature of
about 18° C. The sum of the degree days over periods
such as a month or an entire heating season is used in
calculating the amount of heating required for a building.
Degree Days are also used to estimate air conditioning
usage during the warm season.
- Because of the relationship between temperature and the
rate at which plants grow and develop, the concept of accumulated
degree days has been found useful in quantifying the accumulated
energy of a region or season. Such heat units have widespread
use in agriculture, particularly in the vegetable processing
industry to predict the date of harvest and the timing
of successive harvests.
- Monthly and daily Degree Day values are available from
and Climate stations. The base temperature for monthly
values is 15.5° C.
The method used
in calculating Degree Days is as follows, 4 cases are considered:
- Daily maximum and minimum temperatures
- Daily degree days above and below the base temperatures
- Monthly degree day values and the mean maximum, mean maximum, and mean
The minimum air temperature (Tmin) above the base temperature (Tbase). In this
case there are no degree-days below the base temperature and the degree-days
above are given by 1/2(Tmax + Tmin) - Tbase.
The maximum air temperature (Tmax) below the base temperature. In this case there
are no degree-days above the base temperature and the degree-days below are given
by Tbase - 1/2(Tmax + Tmin).
The maximum air temperature above and the daily minimum air temperature below
the base temperature but the mean temperature which equals 1/2(Tmax + Tmin),
greater than the base temperature. In this case degree-days above are given by
1/2(Tmax - Tbase) - 1/4(Tbase - Tmin) and degree-days below by 1/4(Tbase - Tmin).
The maximum air temperature above and the minimum air temperature below the base
temperature but the mean temperature which equals 1/2(Tmax + Tmin), less than
the base temperature. In this case degree-days above are given by 1/4(Tmax -
Tbase) and degree-days below are given by 1/2(Tbase - Tmin) - 1/4(Tmax - Tbase).
If the mean temperature is equal to the base temperature the same results obtain
using either the formula for Case 111 or Case IV
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