Everett D. Howe

Twenty years of work on solar distillation at the University of California

Abstract Solar distillation investigations at the Sea Water Conversion Laboratory, University of California, began in January 1952 and have continued to the present time. These studies have led to the development of still units of relatively small size, designed for furnishing potable water to isolated residences or small communities. Designs have been completed using wooden frames, precast concrete frames, and precast styrofoam basins. This paper gives information on the construction and performance of the several units; indicates the need for more effective utilization of solar energy; and offers a conceptual design of a solar collector for furnishing low-pressure steam for operation of a seawater distillation plant of advanced design with a capacity of 10,000 U.S. gal. (37·85 m 3 ) per day.

Nocturnal production of solar distillers

Abstract The accumulated production of the deep-basin solar still and that of the tilted-tray solar still with longitudinal baffles are compared. The comparisons show that evaporation in the deep-basin still continues during the entire 24-hour period while the tilted-tray still ceases to produce a relatively short time after sunset. Thus, nocturanal production is a maximum for the deep-basin type and nearly zero for the tilted-tray type. A small experimental still was constructed to determine the factors affecting the nocturnal production of solar stills. The experimental results indicate that a substantial increase of product water could be obtained from the continuous addition of warm water to the still. This increase was found to be a function of flow rate, feed-water temperature, evaporating and condensing areas, and ambient temperature. Using this data, an atmospheric still was laid out to use waste heat from a diesel-electric generator.

Comparison of plastic and glass condensing covers for solar distillers

Abstract This paper compares the productions of several solar stills of different designs, some with double-strength window-glass covers and others with plastic-film covers. Two small identical solar stills were designed and tested over a period of two years. One was covered with a double-strength window glass (0·125 in. thick) and the other was covered with a Tedlar plastic film (0·002 in. thick) which was mechanically treated to produce a wettable surface. Of the four other solar stills tested, three were covered with the Tedlar film and the fourth was covered with the double-strength window glass. These units were of differet designs. Three of them were of the same size (48 sq. ft) whereas the fourth was considerably larger (240 sq. ft). The data indicated that production of the stills covered with the Tedlar film was consistently less than that covered with glass for both small and large stills. The operating and design problems connected with both covers are reviewed.

A solar-assisted heat pump system for heating and cooling residences

Abstract A significant impact of solar energy applications on the total energy demand requires systems or devices which can be retrofitted to existing energy users. The all-electric residence unit, which includes about 10 per cent of all such units in the U.S.A. and constitutes over half of those completed in 1973, seems particularly suited to a solar modification. It is proposed that heating and cooling of the all-electric residence unit be accomplished by using a solar-assisted heat-pump system. The proposed system makes use of a conventional air-conditioning unit which would be modified by fitting controls to reverse the flow of refrigerant for the heating mode and by changing the outdoor heat exchanger from refrigerant-to-air to refrigerant-to-water. In addition, there would be provided a solar collector and two insulated water-storage tanks. Water from one tank would be circulated through the refrigerant-to-water heat exchanger when needed and then returned to the other tank, so that essentially a source of heat of constant temperature would be maintained, thus decreasing the temperature interval for the heat pump and thereby saving energy. In the cooling mode the stored water would be cooled by exposure of the solar collector to the night sky to decrease the temperature interval for the heat pump, thereby reducing energy consumption. Calculations were made for an existing residence unit for which the total energy input is known and to which the proposed solar-assisted heat-pump system is applied. An estimated cost of equipment and of its operation is compared with the cost of owning and operating fuel and electrically heated systems. It is concluded that the solar-assisted heat-pump system with current fuel prices can provide immediate economic benefit over the all-electric home and is possibly on par with residences using fuel oil or liquefied petroleum gas, but it yields higher cost over systems using natural gas. The effect of a two-phase expander to replace the expansion valve in the refrigerant circuit has been theoretically investigated. It shows a significant energy saving worthy of further economic and practical consideration.

The use of energy from salt-gradient solar ponds for reclamation of agricultural drainage water in California: Analysis and cost prediction

Abstract The cost of water from multi-effect distillation (MED) plants of various evaporator designs using thermal energy from salt-gradient solar ponds is calculated. The criterion U C , the heat-transfer capacity per unit cost for the evaporator (ratio of the overall heat-transfer coefficient in the evaporator, U, to the cost of the evaporator per unit area of heat-transfer surface, C) is varied between 12 and 105 kJ/h°C

Chapter 2.4 Measurements and control in solar distillation plants

(3 and 25 kcal/h°C

Solar distillers for use on coral islands

) to evaluate its effect on plant capital cost and performance. Other parameters varied in the study include number of MED effects, solar pond temperature, and cost of steam from the solar pond. Compilation of the results from hundreds of computer simulation runs identify the conditions for minimum distilled water cost and corresponding plant productivity per unit area of solar pond. It is found that minimum distilled water cost results from the use of evaporators with high values of U C . In addition, it is found that distilled water cost is lowest when the brine temperature in the lower convecting zone of the pond is about 60°C (compared to the other temperatures considered of 50, 65, 70, and 80°C). For the case of brine temperature of 60°C, the results show that by increasing U C from 12 to 105 kJ/h°C

Pacific island water systems using a combined solar still and rainfall collector

(3 to 25 kcal/h°C

Solar-assisted still with vapor-compression option

), distilled water cost is decreased from 3.16 to 1.63

An assessment of vapor compression distillation

/ton (11.95 to 6.18