A numerical model of heat storage by buried pipes is developed and applied to the specific conditions of a greenhouse. In the first part, the model is tested against measured data given by an experimental heat-storage greenhouse system. Comparisons between model calculations and experimental results show a good agreement for both the temperature field and the energy exchange rate. Some results on daily and seasonal performance of the system are presented.
The effects of diesel fuel temperature on the efficiency of a 4.4-L diesel engine were studied. Fuel temperatures of 41, 67, and 81 °C were used with engine loads of 0 to 100% of full load at three engine frequencies. Regression equations were developed that predicted fuel economy as a function of PTO power at three engine frequencies. An increase in engine fuel temperature did not improve fuel economy, but did result in reduced fuel mass flow through the injector pump and reduced maximum PTO power. Reducing engine frequency improved fuel economy and supported the ‘throttle back shift up’ technique for saving fuel.
A mathematical programming model was used to forecast the impacts on Ohio's agricultural sector of a moderate increase in alcohol industry demand for corn. Because converting corn into ethanol yields byproduct feeds that can substitute for soybean meal and other commodities, most of the alcohol industry's demand for corn can be satisfied by switching land from the production of soybeans to the production of corn. For this reason, projected levels of ethanol production do not greatly affect crop or livestock prices. This finding is likely to hold for other corn-growing areas in North America.
Diurnal patterns of solar radiation, temperature and humidity are needed for energy and water use evaluations of greenhouses and other agricultural structures, as well as for plant growth simulation studies. Moreover, these diurnal weather pattern data are not readily available for most locations around the world. Somewhat more available are mean monthly values of total daily solar radiation, of maximum and minimum air temperature, and of vapor pressure. Some simple models were taken from the literature and modified to generate diurnal patterns from such data. Model values were then compared to actual diurnal data from a total of eleven locations in New Zealand, Denmark and the United States. For solar radiation a simple half-cosine model had an overall root-mean-square (rms) difference from observations of 16.3 W m−2, but the daylength was adjusted slightly to attain this low rms value. For air temperature, the model of Parton and Logan was modified to force the nighttime decrease in temperature to the minimum near sunrise. This modified equation had an overall rms difference from the observations of 0.64°C. The model for vapor pressure was a simple constant equal to the daily average, and it had an overall rms difference from observations of 0.042 kPa. Diurnal relative humidity values could then be calculated from the constant vapor pressure and diurnal temperature values. Thus, these simple models should be adequate for generating diurnal solar radiation, temperature, and humidity patterns for many applications.
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