Factors influencing greenhouse heating and geothermal heating systems

Low profits, stagnation and other negative consequences of the energy crisis of the early '70s gave renewed impetus to research and development programs in the European countries in an attempt at reducing the energy demand of the rural sectors and discovering new sources of energy. The results of these efforts can be summarized as follows: (1) The specific energy demand in agriculture has been reduced in a number of European countries. New, so-called “energy-saving” technologies have been developed and introduced in plant cultivation and animal husbandry. (2) Renewable resources have been re-discovered and are under exploration or commercial utilization: solar and wind, biomass, industrial waste, geothermal. But the significance of these resources in energy terms is not determined only by the amount consumed and the amount of other resources saved, but also by their role within the economy of the country and the effects on the trade balance. The alternative energies were therefore very much a question of policy, of assessing the influence on more productive sectors and on energy consumption on the whole. These were the factors that determined the different approaches taken in the European nations, and the different results achieved, rather than the availability of the resources. Geothermal energy could make a contribution to the energy requirements of most European countries, for the following reasons: (1) high enthalpy resources can be found in some countries (e.g. Turkey); (2) large quantities of low enthalpy resources at temperatures of 30–80°C can be found in aquifers in most European countries; (3) the rational utilization of low grade heat in district heating, agriculture and process heating could lead to considerable savings of imported fuels, since these sectors account for 40–60% of the total heat demand in Europe; (4) great progress has been made in the last few years in know-how and technology for utilizing different temperature ranges of geothermal fluids in agriculture, animal husbandry, food processing and other applications. It is difficult to assess the future of geothermal energy in agriculture in Europe, in the current world energy market. The factors influencing our assessment vary from country to country, depending on the development stage, short- and long-term policy for resource development and utilization, economic climate, investments available, etc. It is therefore equally difficult to compare the validity of the investment of the various countries in geothermal development and utilization. Much depends on the quality and quantity of the technical, technological and economical information required to reach an accurate estimate. For this reason the first target of the collaboration of scientists from different European countries is to collect all the information available in Europe, then select and reorganize this data in such a way that it can be used by different countries with different local circumstances for different types of assessment. At the present level of technology, there are many possible applications of geothermal energy. The limits change continually with advances in technology. In greenhouse heating, for example, nearly all the temperature ranges required for hot beds and hot water irrigation are actually available, which explains why the most widely developed application of geothermal resources is in agriculture, food processing and greenhouse heating. Many projects in European countries are successful, showing profits. However, the main drawback is the relatively high investment costs compared to conventional heating systems. Some technical problems have also to be solved in order to achieve the specific light, ventilation and other conditions required in greenhouse systems. An important factor in low-temperature installations is location of the installation, which affects climatization and heat transfer. This paper will discuss the different aspects of this problem.