Feasibility of using heat-recovery exchangers in livestock buildings at a site at a specific altitude with a specific average outdoor air temperature

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 which the 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.