A project report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, 2016 / Underground chilling installations have an important role in deep mining operations because the total cost of cooling a mine is minimized when underground machines deliver as high a proportion of the required cooling as practicable. Thus the refrigerating load of an underground installation should be maximized to the extent permitted both by the environment in which the installation operates, and by the physical characteristics of the machines in the installation. This study analyses how, and to what extent, the refrigerating load of older, already installed water chilling machines rejecting heat into a limited supply of return water may be maximized through configuration of their water circuits and capacity control of their compressors. Multiple-machine installations are simulated in a range of scenarios, using the thermodynamically efficient series-counterflow arrangement, to predict both the potential maximum refrigerating load and the expected refrigerating load of such installations. The simulation results indicate significant potential for installations to chill water more efficiently and thus deliver larger, maximized, refrigerating loads. For scenarios where a larger-than-design flowrate of return water is available, so permitting machines to be operated with little or no capacity control, the simulated chilling efficiency and thus the expected refrigerating loads tend toward, and in some cases almost match, the potential maximum values. For simulations in which compressor capacity control is used to prevent the return water temperature from exceeding its maximum permitted value, expected refrigerating loads fall short of their potential values, by varying amounts, due to the low machine cycle efficiency caused largely by reduced compressor isentropic efficiency at part load. For a limited supply of return water for heat rejection, the simulations indicate that load maximization efforts should focus on the machines in an installation being connected in a series-counterflow arrangement and operated, as far as practicable, at or near full capacity to create the best prospect for approaching potential maximum refrigerating load.

Wind activated rooftop ventilators have recently been rediscovered as appropriate energy conserving alternatives and/or supplements to power ventilation. Designers of passive solar heating/ cooling systems, for instance, often use ventilators in various ways as important components of their systems. Unfortunately, results with present types of ventilators are often less positive than expected. In recent wind tunnel tests the commonly available turbine type ventilator, in a 10 mph wind, moved only 20% more air than an open stack with no ventilator at all. Given the turbine's poor showing, the development of a ventilator with significantly improved performance was seen as feasible and was adopted as the focus of this project. An extensive literature search revealed several design principles established by others in comparative tests dating as far back as 1842, and the existence of over 300 patented ventilators designs. For this project a speculative ventilator design was evolved incorporating (1) criteria established after preliminary tests, (2) the above mentioned design principles and (3) three new concepts. Eight 1/3 scale ventilator cowls were produced in molded fiber reinforced plastic and altered in various ways in an attempt to optimize performance. Also tested were a variety of simple forms and three experimental types that had previously been tested at a larger scale. The models were tested in a 3-foot diameter open-throat wind tunnel on a 4-inch diameter air shaft or "stack." Results are given in stack velocity, volumetric flow, and percentages of enhancements over an open stack. The percentage enhancement values allow ventilator tests done at different scales to be compared. / M.Arch.

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