Summary:

The installation of an energy-saving facility must be preceded by analysis
of its financial effectiveness. Among methods enabling such evaluation is the
basic net profit calculation method. For this, the annual consumption of electricity
for ventilation or of thermal energy for heating must be determined. The calculation
formula uses the sum of energies for temperatures within the range from
the calculation temperature for the area in question to the long-term average of
the maximum temperature at the site, or to the temperature at which the heating
power is zero. It is necessary to know the summary time of occurrence of a given
temperature during a year. The site data can only be assessed based on long-term
meteorological information. In fact, data used by current national standards to
describe climatic conditions in the Czech Republic are from the years 1901 to
1950.
The dependence of the average yearly temperature on altitude is shown in
Fig. 1 for the 1961 – 1990 and 1991 – 2000 periods. It is evident that the average
temperatures for the latter period are nearly 0.6 K higher than those for the former
period, irrespective of the altitude.
In this paper the climatic conditions are assessed based on daily data
measured throughout the period from 1 January 1991 to 31 December 2000.
Weather stations were selected so as to achieve a uniform coverage and continuity
of measurement at each site (as far as possible). All the stations lie in the
Czech Republic between 48.8° and 50.8° north latitude at altitudes from 158 m
to 1324 m. It was the objective of this examination, based on the meteorological
data collected to calculate the average number of days and hours during whichthe temperature during the year is lower than a specific limiting level, in
dependence on the average yearly temperature of the site.
Fig. 3 shows the average number of days in a year during which
a temperature lower than a selected limiting level occurs, as calculated for the
1991 – 2000 period. The results are presented for 4 areas with average yearly
temperatures of 6 °C – 7 °C, 7 °C – 8 °C, 8 °C – 9 °C, and 9 °C – 10 °C, respectively.
The graphs enables us to ascertain the number of days during which
a heating facility is in operation if the facility is activated by outdoor air temperature
decrease to below a specific limiting level.
If a typical daily temperature wave is considered, the method makes it possible
to estimate the number of hours during which the air temperature is lower
than the limiting level chosen. The difference between the data for various limiting
levels allows us, for an area with a specific average yearly temperature to
ascertain the time of occurrence of outdoor temperature within various ranges.
The results of calculations are shown in Fig. 4 and Table 1.
The method applied enables underlying data to be prepared for the assessment
of energy demands for air heating at a given site and for estimation of the
energy savings that could be achieved by installing economical air heating facilities
in livestock buildings.