Analysis of solar thermal systems for domestic hot water production in a nursing home

The current state of climate change urges the world to consider alternatives concerning the use of energy. In Norway, electricity is a common energy source in buildings, but heating is a purpose which can be conducted using other energy carriers. In 2017, SINTEF Byggforsk and NTNU initiated the project VarmtVann2030 to improve the knowledge about the use of domestic hot water (DHW) in the country. This thesis examines the possibilities of using solar collectors as energy source for the heating of DHW in a nursing home. Some of the results are based on measurements carried out on a nursing home in Drammen, as a part of VarmtVann2030. The capacity of the sun is 15 000 times larger than the earth’s population’s total need for energy. Solar collectors transform radiation energy from the sun into heat, which again is transferred to an energy carrier, most often a liquid. A solar thermal facility is usually dimensioned to produce 300-600 kWh/m2sc and cover 40-60 % of the energy needed for DHW during a year. The annual DHW energy demand for the Drammen nursing home is 53.9 MWh. The existing standard on DHW energy use at nursing homes, SN/TS 3031, gives consumption values which are almost twice as large. Simulations were done using a software called Polysun Designer and calculations were performed in Excel. The focus was on a pressurised system in combination with an electric water heater. A solar thermal system was chosen based on advices from SGP Armatec, a supplier of pressurised installations in Norway. SGP Armatec also offered examples of prices of materials. Considering different sizes of solar collector areas and accumulator tanks, the most profitable solution was found. The most profitable system was the one with the lowest Levelised Cost of Energy (LCOE) out of solar collector areas of 10-100 m2 with accumulator tank dimensions of 50 l/m2sc, 62.5 l/m2sc and 75 l/m2sc. The best tilt angle was found doing specified simulations. In addition to the LCOE, the payback period and annual cost were considered. Technical parameters included in the results were the solar fraction, area specific collector field yield and maximum collector temperature. The most profitable system based on the collected consumption data from the nursing home consisted of a solar collector area of 40 m2 with a tilt angle of 50° and an accumulator tank of 2000 l. For this solution, the LCOE was 66.9 øre/kWh, the payback period was 23.2 years and the annual cost was 17 798 NOK/year. The solar fraction was 38 %, the area specific field yield was 512 kWh/m2sc and the maximum collector temperature was 90 °C. Alterations in accumulator tank volume and collector area gave various effects in the parameters. A large tank gave the best technical performance because of the increased storage capacity and the lowest economic values occurred for a tank of 1500 l. Regarding construction size, a small system achieved better outcomes than a large one due to its adaptation to the DHW consumption, but the one at 40 m2 was most profitable. For the large system (80 m2), the LCOE was 75.7 øre/kWh, the payback period was 27.2 years, the solar fraction was 56 %, the area specific field yield was 388 kWh/m2sc and the maximum collector temperature was 130 °C. For the small system (20 m2), the LCOE was 73.9 øre/kWh, the payback period was 26.3 years, the solar fraction was 22 %, the area specific field yield was 594 kWh/m2sc and the maximum collector temperature was 76 °C. The annual cost was subject to negligible changes for different system sizes. Sensitivity analyses were done on the most profitable system for both the investment cost and the electricity price, with alterations of ± 30 %. Not surprisingly, all the economic parameters favoured a low investment cost. The minimum values were an LCOE of 46.8 øre/kWh, a payback period of 15.2 years and an annual cost of 15 928 NOK/year. For variations in the electricity price, changes in the LCOE was negligible. The payback period and annual cost was subject to larger effects, their lowest values being 16.9 years and 14 329 NOK/year, respectively. Additional outcomes of the thesis research gave indications that the DHW consumption should be of a certain magnitude for the use of solar collectors to be adequately profitable. A tripling of the Drammen nursing home DHW demand gave an LCOE of 53.3 øre/kWh. Simulations of a demand based on SN/TS 3031 gave reason to believe that the standard overestimates the best size of solar thermal facilities for nursing homes. SN/TS 3031 resulted in a most profitable system size of 50 m2. All the parameters, with an exception of the annual cost and solar fraction, achieved worse results than expected from the standard when implementing the measured DHW consumption on the 50-m2 construction. This kind of estimation of the demand can give very different outcomes than predicted. The results in this thesis show the importance of enhanced research on the use of domestic hot water. Both costs and use of energy can be minimised if the actual consumption of the building in each individual case is examined in advance of the installation of a solar thermal construction. A decrease in the costs of solar thermal facilities and/or an increase in the electricity price would make it a more desirable alternative