Evaluation of alternative sanitary water heating configurations for demand side management

Abstract

The largest percentage of sanitary hot water used in South Africa is heated by means of electrical resistance heaters. This is one of the major contributing factors to the undesirable high morning and afternoon peaks imposed on the national electricity supply grid. Water heating therefore continues to be of concern to Eskom, currently South Africa's only electrical utility company. New water heating technologies have been developed for large-scale sanitary water heating in the form of the so-called in-line heater (ILH) and stratified in-tank (SIT) configurations. The purpose of this study was to evaluate the performance of these newly developed water heating technologies under load shedding conditions. The performance of the ILH and SIT water heating technologies was evaluated via an existing simulation model under load shedding conditions. Furthermore, an extensive empirical investigation was conducted on a number of real-world water heating plants in order to evaluate the actual performance of the ILH-configuration. The results obtained via the empirical investigation were also employed to further verify the existing simulation model. A new model simulating the standing heat losses suffered by water heating systems was developed. The model can be used to simulate the standing heat losses suffered by a typical centralised water heating facility with good accuracy. It was found that the ILH-technology performs excellent under load shedding conditions. The ILH-plants under investigation were able to shed their entire load during peak demand periods while still supplying the occupants with sufficient hot water throughout the day. The SIT-technology proved to be a good alternative where the ILH-technology is not economically viable, realising the maximum load shedding potential in under-utilised water heating systems. It was also found that the implementation of these water heating systems on a national scale would provide the utility with substantial load shedding potential. The facilities at which the systems are installed would also benefit greatly with annual savings potential on electricity cost ranging from 8.5% to 24%.