Potential for load shifting in ventilation and cooling systems

Abstract

One of the major role players in the economy of South African is the mining industry. It forms almost 20% of the gross domestic product of South Africa, with sales of R 76.5 billion for 1999. Of this, gold sales were 33% of the total sales, or R24.99 billion for 1999. Platinum sales were 19.5% of the total sales, or RI4.92 billion for 1999. In 1999 the energy consumption of the mining industry in South Africa was 114 325.2 TJ or 31.757 TWh per year at an average consumption of 3.63 GWh. This constitutes 18.4% of the country's total energy consumption for 1999. This forms a big part of the annual expenditure of the mining industry and contributes a large part of the base load of the country. ESKOM is moving towards a price structure for electricity that reflects the real cost of generation, namely real time pricing (RTP). ESKOM developed various cost structures to coax customers to manage their electricity demand (DSM) to use more energy in off-peak periods (low cost of generation) and less energy in peak periods (high generation costs). To use these structures to the fullest potential, the mines need to investigate their energy consuming components and see where these structures can be implemented. The ventilation and cooling (Ve) system of mines use approximately 25% of the total energy used in the mining activities. This component is therefore a good place to investigate the implementation of such structures and their potential impact. Most of the price structures from ESKOM are based on the fact that the consumer needs to be I able to shift part of or its entire load for a period of time. The potential of this shift and the impact of it on the mine and ESKOM is complex and dynamic in nature. For such a purpose integrated, dynamic simulation software is needed. In the mining industry there is no integrated and dynamic simulation software. This simulation field is much more developed in the building industry. Therefore, with much effort, a building simulation tool" was used to find the potential for shifting load in gold and platinum mines. A first pilot study was done for the VC system of a pilot mine, South Deep (PDW AN). The mine has an installed cooling capacity of 28 MW and had a total energy consumption of 400 GWh for 1999. The mine was simulated and verified with measured results. The VC system or cooling cycle attributes almost 40 % of the total load caused by the mine. Using current and new control, along with some different system configurations, the total potential load shift on VC was determined to be 19 MWh, sustained for five continuous hours per day. This causes a recovery period of six hours with an increase of 4.5 MWh on the maximum load. If this could be replicated on all the mines in South Africa, a total load shift of 1,35 GWh could be achieved. But not all mines are that deep and therefore the influence of the cooling cycle might not be so great. If only half the potential load could be shifted it could still cause a load shift of 676 MWh for the South African network for a potential period of five hours a day. Only when the entire mining industry is able to achieve the same results as South Deep, can ESKOM successfully implement all their new pricing structures and can South Africa profit from such devices. Our experience with this project also showed that a new integrated, dynamic simulation tool, aimed specifically at mines, must be developed before the above mentioned results can be achieved by ESKOM.