The problem of energy consumption during heating and cooling with bang-bang control based upon room air temperature is studied. An analytical model is solved using the Laplace Transform technique, yielding an exact solution to the system. TMY weather data are used from four locations during the months of August and January to assess climatological effects. Approximate models are developed to explain the time lags observed during free response, and the observed chattering rate under bang-bang control. Results indicate the presence of a thermal mass effect due to the nonlinear interaction between the thermal wave penetrating the wall and the control function, with a greater effect for walls of massive construction, and in moderate weather conditions.
Incorporating the effect of diurnal variations and annual variations of the environmental parameters (in a way similar to the analysis of amplitude modulation), the performance of an earth-air tunnel of infinite dimension along the horizontal direction has been analysed; dimensionless parameters have been used. The effect of earth storage on the performance of the tunnel has also been taken into account. The effect of modifying the earth's surface conditions, by wetting and shading, on the performance of earth-air tunnel system has also been investigated under two conditions: first when the inlet air is drawn from the ambient, and secondly when it is drawn from a conditioned room for recirculation to the room.
A computer simulation study has been made for an open-cycle absorption solar-cooling system operated in a humid area. The system configuration is similar to the one proposed by Wood at Arizona State University. The system with a glazed solar collector/regenerator shows sufficient solar regeneration capacity for operation in Kaohsiung, Taiwan. Many parameters controlling the system performance have been studied, including the amount of solution storage, absorber effectiveness, absorber solution flow rate, and the thermal capacitance of the structure. System simulation, using average local weather data, shows that the solar system can provide 75 to 97% of the cooling load needed for the summer season (from May to October) under various operating conditions.
A new technique for optimizing silicon solar cell performances has been established. The parameters to be optimized are replaced by independent variables without constraints. The variables include diffusion and recombination parameters, as well as non ideal effects such as band gap narrowing. The method allows a simultaneous optimization of parameters leading to maximization of solar cell efficiency and open-circuit voltage. It suggests an allowable range of the efficient parameters, and a new cell design criterion in terms of a thin base with a low recombination velocity.
Part 1 was published in Int. J. of Solar Energy, 8, (3), 1990 Input/output diagrams are very useful for evaluating the daily performances of solar collectors. We present a simple and accurate method to generate such diagrams for solar collection subsystems. The introduction of new dimensionless variables leads to a simplified and universal expression of I/O diagrams. The performances of the entire solar systems can then be evaluated by combining I/O diagrams to day by day simulations, which is very helpful in order to check existing installations or for design purposes. All these procedures are based on and validated by experiments, measurements and studies performed over many years. Now that we have described the main characteristics of a solar collection subsystem we are going to focus only on the solar collection subsystem as a whole, in order to analyse and evaluate by means of the G3-Model, its daily performances.
The status of techniques for the production of sheets, ribbons, and foils of silicon for solar cells is reviewed. Technical problems and economic constraints are analyzed. The horizontal support web technique relies on a wedge-shaped growth interface which decouples the pulling velocity and the growth velocity which are nearly perpendicular to each other. The growing ribbon floats on a silicon melt that is contained in a long silicon crucible and is withdrawn to one side. In the ramp assistant foil technique, the silicon melt is contained in a relatively flat crucible that is open on one side. A preheated substrate is moved across this opening, and some of the melt solidifies on the surface. The silicon-sheets-from-powder technique starts from Si powder or granular silicon (grain size: 50-500 mu m). Three steps are needed to obtain the final ribbon. It is concluded that although the basic ideas as well as the results of these three methods are very distinct, evaluation of their respective merits is difficult.
