Integrating Solar Energy in Hot Water Generation by a Steam Boiler: a Case Study of a Hospital

Abstract

In many countries, efforts are being made to limit the use of fossil fuels as a source of energy. The use of fossil fuels for many years has led to increased emissions of gases responsible for climate change. In a number of cases, the reduction in use of fossil fuels is being compensated for by using renewable energy; especially solar and wind power. Among high fossil fuels users are hospitals that use fuel fired boiler systems to produce hot water and steam, which are vital utilities in hospitals. Among alternatives to thermal energy source for hospitals is solar thermal heating. Though solar is a clean source of energy, its variability and dependency on weather makes it impossible to fully replace fossil fuels. However, if well integrated to existing systems, can significantly reduce the fuel use. The objective of this study was to evaluate the viability of integrating a solar thermal system to an existing fuel fired hot water/steam boiler system in a hospital (H1). Three hospitals were involved, all located in Nairobi. Two of the hospitals use fuel oil while the third use electricity to generate hot water. The hospitals, H1, H2 and H3 have bed capacities of 225, 176, and 103, respectively. Hospitals H1 and H2 have a fuel fired boiler systems, while H3 has an electrically heated boiler system. Energy costs for thermal water heating for hospital H1 and H3 were US$ 0.88 and 2.14 per inpatient bed day, respectively. There were no records for thermal water heating for hospital H2. A thermal solar heating system contributing a 40% heating component for was designed for integration to Hospital H1. The initial investment cost was US$ 60,197. Economic analysis showed that the annual energy cost saving would be US$ 23,766. This would lead to a simple payback period of 2.53 years and a return on investment (ROI) of 39.5%. At a discount rate of 15%, the net present value of the integrated system would be US$ 59,083 with an internal rate of return (IRR) of 40%. The study established that electrical water heating was more costly per inpatient bed day compared to thermal heating. Integration of solar heating to thermal heating at a 40% contribution would save 945 GJ per annum equivalent to 75.5 tons of CO2. The analysis indicated that incorporating a solar heating system to the existing heating system for H1 is economically feasible. A comparative study on energy saving on a working solar integrated water heating system is recommended.