NETWORK DESIGN Marafeq Qatar designed the distribution network of approx. 170 kmwith strategically placed loops and isolation valves. To assure high quality, Marafeq Qatar selected an all welded pre-insulated steel piping system with integrated leak detection system; all certified in accordance with the EN 253 family of standards. The key to EN 253 is that the pipe is fixed in place by transmitting strain energy from thermal expansion / contraction to the ground through the insulation. If the bond between the insulation and the pipe or casing fails then the pipe slips and strain energy is transferred to pipe bends or valve bodies. Marafeq Qatar also discouraged flanged connections except in special cases. Extensive industry practice in Europe has demonstrated flanged valves installed in chambers are weak links in the distribution system, and the European trend is to use an all welded system.
In line with the local codes to save precious potable water, make up water in cooling towers is designed with Treated Sewerage Effluent (TSE) water supplied by the local utility company. Chiller plants are designed with Ultra Filtration and Reverse Osmosis systems to filter and polish the TSE water to protect the major equipment from potential fluctuation in TSE water quality. TECHNICAL CHALLENGES Lusail City is developing across large areas (both north and south) which meant Marafeq Qatar had to closely communicate with the master developer about the changes in master plan and phasing. Changes in the master plan and phasing schedules required modifying the District Cooling System phasing strategy. Plants’ capacity phasings were continuously monitored and updated along with the main utilities required—power, water and drainage.
Coordinating the various segments of the distribution network also proved challenging since the network was divided into multiple construction packages, and these were in various stages of development. Interconnection of these sub packages into one network and preserving the earlier completed networks proved to be challenging. Since plot locations for distribution plants were somewhat limited, Marafeq Qatar had to carefully analyze network design and pumping to make sure all customers could be served and with some margins to allow for the inevitable changes that come with such an immense effort as Lusail City.
PLANT PRODUCTION DESIGN When planning the plant production, Marafeq Qatar assured the design was well thought, incorporated with redundant elements in order to maintain chilled water availability, and with design lives of 25 years for electrical and mechanical equipment and 50 to 60 years for civil works and pipelines. To minimize the impact on the electrical system grid, the Lusail City district cooling system will use stratified chilled water Thermal Energy Storage (TES) to shift demand from the peak period to off-peak periods. Although the primary benefit of TES is peak shaving, using TES benefits efficiency because chillers can operate more often near maximum efficiency region and can operate more often in the evening (off-peak period) when wet bulb temperatures may be lower, which makes the entering condenser water temperature lower and the chiller efficiency higher.
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