Energy in Agriculture最新文献

Recovery of heat from animal houses takes place in 1% of all Danish farms. At the beginning, which means in the Seventies, air/water evaporators of copper-aluminium were mostly used. Because of problems with corrosion, most of the heat pumps today are water/water types with external heat exchangers of artificial material such as PVC and PEL.

Field testing is complete with 17 heat pumps for animal houses, and experiments with an additional 20 units have been initiated. The results show that the mean effect factor is 2.3, taking into account the total energy consumption for compressor, ventilator, circulation pumps etc. The mean effect factor concerning the compressor alone is 3.0.

In the near future an effect factor of 2.5–3.0 seems to be possible.

Significant developments of the past decade in the area of solar crop drying are reviewed. Increasing energy prices stimulated research on solar drying in highly mechanized agricultural systems. However, in those countries solar drying has to compete with automated crop dryers using fossil fuels as the energy source. Studies have shown that neither the temperature required nor the quantity of heat necessary in high-temperature batch type or continuous-flow dryers can be reached with solar collectors. Therefore solar energy cannot be adapted economically to high-temperature drying systems.

Solar energy is considered more applicable to low-temperature in-storage drying systems which has gained more importance in the last decade for drying grain and hay.

Conditions in tropical and subtropical countries make the use of solar energy highly recommendable. The introduction of solar crop dryers seems to be a way to lower mass losses compared to traditional drying methods and improves the quality of the product considerably. Solar drying can be a way to increase the food supply and it also can be a possibility to increase the income of the rural population.

The main applications for solar collectors in agriculture are drying of agricultural crops and for the heating of animal houses with great energy demands. Different types of active airtype solar collectors have been examined for these applications. In both cases there are benefits if the solar collector is integrated into the building. The types which have been tested have the potential to compete economically with oil as a heat source.

For greenhouse heating with solar energy, different techniques can be used: separate solar collectors, solar collectors integrated in the greenhouse, and the use of the greenhouse itself as a solar collector. These techniques are described and results are presented for climatic conditions in Germany and Mediterranean countries.

Studies conducted during the last few years show that the various ecological conditions in Romania determine different pathways of energetic phytomass production and transformation into fuel. There are approximately 22 million ha of land covered by terrestrial vegetation of which 10 million is arable land and one-fifth of this is of poor productivity. Waters (lakes, ponds, rivers) cover approximately 0.7 million ha. The technologies used for the production of energetic phytomass from various agricultural, forest and aquatic species tend to yield 20–25 t of dry matter for the terrestrial forms and 20–40 t of dry matter for the aquatic ones (Pistia, Eichhornia, etc.); this represents a mean annual output of 2000–2500 l of ethanol per ha. The investigations performed so far suggest the main phytomass sources to be explored for obtaining the various forms of energy; e.g., for agricultural lands having a high fertility, the following species were shown to be important from an energy point of view: sugar beet (roots), sweet sorghum at the milk-dough stage, kernel maize, Jerusalem artichoke (tubers and green above-ground parts), potatoes (tubers), and oil rape. Some laticiferous plants are also being studied. On fertile soils in the southern irrigated areas, high yields of energetic phytomass were obtained in stubble crops with maize, sorghum × Sudan grass and grain sorghum.

Special attention is paid to the utilization of the pulp which remains after sweet juice extraction from plants for alcohol fermentation. This pulp may be used as fresh forage or may be ensiled.

Investigations are being conducted with a view to improving the fertility of poorly productive soils, which cannot be used for agricultural purposes at the present time. Species with a rapid growth, such as poplar, willow and osier are being grown on river meadows and in the Danube Delta. Studies aimed at the energy utilization of wood and plant wastes remaining after harvest (straw, cobs, stalks, branches) are also being conducted.

This paper discusses the design of hybrid solar greenhouses with subsurface heat storage. The thermal analysis is presented followed by a description of the flow of the control operations. Finally, a microcomputer controller is designed which is capable of implementing the necessarily fairly complex control strategy.