Objective To demonstrate on three inhabited houses;- the contribution that a thermosyphon solar-energy water heater can make to satisfy typical domestic hot-water requirements;- the effect of different hot-water consumption patterns on the long-term solar-energy contribution to the domestic hot-water requirement;- the reliability and effectiveness of three different methods of protecting the system from damage due to freezing of the circulating liquid.To provide a realistic data base upon which a detailed economic analysis can be undertaken, and criteria for selecting heating systems established according to locality.Total energy production was 0.2 TOE/year; payback 48 years.INSTALLATION PROCEDUREThe total installation time of one system was approximately 2 man days. But considerable time was additionally lost due to bad weather conditions, insufficient material delivery and waiting time of the arrival of tradespersons with particular skills. A further substantial reduction of these 2 man days seems unrealistic. Skilled and interested workmen are of highest importance for a solar installation.INSTALLATION EXPERIENCEThe collectors weight was 63 kg, which is very heavy and therefore difficult to handle. The glass reinforced plastic collector box was prone to cracking at the mounting points. The piping connection to the collector was too short. Hence the collector employed did not ensure a simple and efficient installation. The collectors were left empty on the roof during three weeks. Laying stagnant under levels of high insulation, the selective coating (MAXORB) did not withstand the high temperature of 150 C, it began to wrinkle and to peel.FROSTPROTECTIONOnly the glycol filled installation withstood the frost periods during winter time. The drain down system as well as the electric heating system failed and these two solar system were seriously damaged.USER RESPONSEThe handling of a third tap for solar heated water proved to be not practical. The user had to wait when using this tap, and was never sure if the solar heated water was at an acceptable temperature level. A remote temperature indication is necessary for such kind of installation. A preheating mode yields higher solar fractions.THERMAL RESULTSThe overall solar fraction was expected to be 40%. After thirteen months of monitoring the average of the glycol filled third tap installation was 17% with a maximum of 37% in July 1986. The highest daily solar fractions recorded for the different houses were 92%; 57%; and 68%. The third tap installation was not successful due to the negative user response. The overall efficiency of all system has to be considered aspoor, but could be improved by optimizing the different componants e.g. by a better thermal isolation of the total installation in the loft. The monitoring results of the solar plants yielded a payback time between 35 and 48 years.Three basically identical thermosyphonic solar-energy water-heating systems have been installed on three adjacent dwellings. These houses are owned by the Cranfield Institute of Technology and are normally occupied by married students and their families. During the three year monitoring period the three houses were occupied by five different families, thus the effect of up to five different patterns of hot-water consumption on the system's performance could be demonstrated. These houses are typical of many in rural areas of Europe in that they are some distance away from a mains gas-supply. All three houses employed originally coal-fired back-boilers for water heating with an additional electric immersion element water-heating : both these systems being manually controlled. One of the dwellings has since been converted to oil-fired to radiator central and water heating. Each of the three systems installed provide 1.8-2.0 GJ per annum which constitutes approximately 20% of the annual energy requirement for hot-water production of each dwelling.In two of the houses the solar-heated water is provided directly to the points of use by means of a third-tap on the bath and the basins. The occupants of the houses receive instructions to try the third tap first when hot water is required, running it for a short while to draw off any cool water in the supply pipe, and then (if the water temperature is hot enough) continue to use it until the temperature falls below that desired.Each system comprises the following elements :A 4m2 flat-plate solar-energy collector single-glazed with a selectively coated surface. Each unit is mounted "on-tile" with fixing bolts through the rafters. The roof is properly sealed and weather-proofed.A 200 litre hot-water store and vent, insulated on all surfaces by a 5 cm thick layer of fibrous insulant.A 12 litre independent unpressurized cold-water header tank.A hot water supply pipe to provide solar-heated water to three additional taps located above the kitchen sink, the bathroom hand-basin and the bath respectively in two of the dwellings.All thermosyphon flow circuits are manufactured from light gauge 22 mm diameter copper to reduce flow resistance. There are no acute pipe bends and all pipe-work is approximately inclined to prevent air locks. A drain facility is provided in the lowest point in the thermosyphon flow circuit. The systems installed also differ in their respective methods of preventing damage due to freezing. In one unit, an electrical heating element taped to the lower header of the collector, heats the water in the collector when the temperature falls below zero. The second system is of the automatic "drain-down" type. The third system contains antifreeze and heats DHW via a heat exchanger. Programme(s) ENG-ENALT 2C - Programme (EEC) of demonstration projects relating to the exploitation of alternative energy sources and to energy saving and the substitution of hydrocarbons, 1983-1985 Topic(s) 6.2 - THERMAL Call for proposal Data not available Funding Scheme DEM - Demonstration contracts Coordinator Cranfield University EU contribution No data Address Silsoe Campus Wharley End MK45 4DT Cranfield United Kingdom See on map Total cost No data
