Optimization of the in-line sanitary water heating system for demand side management in the South African commercial and industrial sectors

Abstract

It is currently estimated that South Africa will be running out of surplus electrical capacity by the year 2007. This estimate is based on the current growth in economy that primarily includes the electrification of half-a-million new households per year, with a final target of 5 Million households by 2007. This situation is forcing ESKOM to take action to reduce peak electrical demand by initiatives such as the implementation of Demand Side Management (DSM) programs. These DSM programs are currently aimed at the industrial and commercial sectors where bigger impacts in load shifting can be achieved than in the residential sector, which is the actual cause of the surplus capacity run-out. The reason for this is that the large amount of individual consumers in the residential sector presents several barriers to the implementation of DSM programs in this sector. 7his study addresses the optimisation of sanitary water heating systems in the commercial and industrial sectors, for DSM purposes. Commercial and industrial applications are considered separately, since a difference in application strategy emanates from the different tariff structures utilized in the industrial and commercial sectors. In the industrial sector where the focus lies on load shifting, an in-line electrical resistance heater will be utilized. In the commercial sector where the focus lies on both load shifting and energy efficiency, a combination of heat pumps and in-line electrical resistance heaters will be used. In both applications the heating equipment is connected in the so-called 'improved in-line heating' configuration developed in previous studies. The first part of the study provides results obtained from sanitary water heating DSM projects that were completed at several commercial and industrial sites. Firstly new hot water consumption patterns for hotels and mine residences are provided. The differences between these profiles, and those found in previous studies for the residential sector, were highlighted. This was achieved by a simulation study, which resulted in a design envelope for the most important system specifications, for different hot water consumption profiles. Results for in-line heat pump water heating systems installed in commercial buildings were then provided. These results show that direct benefits for both utility and building owner can be achieved in terms of peak demand reduction. Additional benefits are also obtained by the building owner in terms of energy efficiency improvements due to the utilisation of the heat pump unit. Results for a utility funded DSM project to install in-line water heating systems at several mine residences were then provided. A significant DSM load shift was achieved by this project, to the benefit of ESKOM. The results showed how the in-line heating systems enabled load shifting out of utility critical periods without any loss in hot water availability to system users. Part two of the study provides results of optimisation studies for sanitary water heating system design in both commercial and industrial sectors. This is achieved by first of all developing a water-heating system simulation program bared on simplified first law analysis. This model successfully demonstrated a high level of accuracy for hoth electrical demand and thermal availability prediction, for different configurations of sanitary water heating systems. Simulation results were verified with measured results obtained from the commercial building and mine residence projects as provided in part one of this study. The new simulation program, together with the new hot water consumption patterns for hotels, was then used in an optimisation study for commercial building water heating systems. The study provided optimal heating and storage capacities for a broad range of system parameters. The most optimal solution for designing a completely new water heating system was also provided. The study also showed that additional control upgrades resulted in improved cost- and energy efficiency for the system. Favourable economic returns are obtained by the proposed retrofits; an Internal Rate of Return of at least 47.1% is achieved for the different tariff structures employed in the commercial sector. Finally, a digital control algorithm was developed that optimises operational cost efficiency for sanitary water heating systems in the industrial sector, subject to Real Time Pricing (RTP). The study showed that significant savings are possible; a theoretical operational cost reduction of 20%-29% can he achieved at the case study plants. Cost reductions are mainly a function of system utilization: bigger non-dimensional heating and storage capacities result in higher savings potential. The optimisation studies done in this thesis provide 'real world' solutions with a well-balanced trade-off between simplicity and efficiency. Well-evaluated options for DSM programs in the different sectors are therefore presented, which can obtain benefits for both electrical utility and client. These options should therefore he able to boost the viability of sanitary water heating system DSM projects in the South African Energy Services Industry.