COOLING TOWERS | WATER CONSERVATION In contrast, the USGBC Leed certification requirements have included a specific water efficiency credit for CT water usage. The intention of the credit is to conserve water used while controlling microbes, corrosion and scale within the condenser water system. One point is available if the following five parameters are not exceeded in the maximum concentrations up to a maximum of 10 cycles. This requires water analysis to be carried out, including measuring maximum concentrations. Alternatively, two points are available under the following two options: 1) I f a minimum of 10 cycles of concentration can be achieved by the CT by increasing the level of treatment 2) Meeting the maximum number of cycles with 20% recycled non-potable water. Option Treatment method Chemical Notional treatment only Total water supply use Regeneration RO waste water concentrate water CT bleed water Total recoverable waste water m3.h-1 m3.h-1 m3.h-1 m3.h-1 m3.h-1 21.72 0.70 Nil 5.95 0.70 6.1 Chemical with RO treatment 15.30 0.59 1.47 1.32 2.06 6.2 Chemical with packaged side 16.47 stream and membrane filtration 0.62 Nil 2.03 0.62 6.3 Chemical with packaged side stream and EM treatment 19.87 Nil Nil 7.95 Nil 6.4 Ozone treatment 15.49 0.59 Nil 2.98 3.57 6.5 Ozone treatment with RO pre-treatment 15.30 0.59 1.47 1.33 3.39 Table 1: Water use and recovery summary (excluding water use recovery systems) A 20% water saving is significant when you look at the volume of water used for the evaporative cooling process. To give consideration in terms of a single solution is difficult, due to the cost implications with the proposed treatment options, and the material selections required to suit, having impact on both capital and operating costs. To summarise, there are a number of considerations to be taken into account when seeking the optimum solution, which will vary according to project requirements. Each water treatment option would be suitable for use as CT water make-up but, if combined with other water-recovery systems within the building, the overall consumption of potable water for mechanical uses can be reduced by approximately 22-33%. Significant water savings are possible withthe water treatment options considered, with annual water costs being reduced by up to 14,000. It is worth noting the notional building analysis used UK weather data, and savings would be even greater in other regions such as the Middle East. Additionally, all the options are above the minimum 20% recycled water figure required to achieve the additional Leed credit for water efficiency associated with CT water use. Such solutions will become more common as the sustainability accreditation for new developments drive the need for these watersaving methods. A combined approach, which includes this water usage within the overall project water balance, will make a significant contribution to reducing overall water consumption in new buildings. CJ A NDREW RUSSELL MCIBSE MSOPHE is a project director at Hilson Moran in Qatar and has an active role in the SoPHE Middle East regional group Recovered water contribution Annual water use using recovered water Annual water supply saving m3 m3 % 5,505 576 28,237 24 3,029 5,505 576 21,632 30 33,125 3,029 5,505 576 24,015 28 Chemical with packaged side stream and EM treatment 41,526 3,029 5,505 576 32,146 22 6.4 Ozone treatment 31,140 3,029 5,505 576 22,030 29 6.5 Ozone treatment with RO pre-treatment 27,670 3,029 5,505 576 18,560 33 Option Treatment method Annual water supply use Annual rainwater harvested Annual greywater harvested Annual condensate harvested m3 m3 m3 Notional Chemical treatment only 37,347 3,029 6.1 Chemical with RO treatment 30,742 6.2 Chemical with packaged side stream and membrane filtration 6.3 Table 2: Total water use and recovery summary (using water recovery systems) Rainwater harvesting Greywater harvesting Condensate recovery 2% 13% 9% Potable water supply Water softeners Cooling tower water make-up supply Cooling tower water make-up storage 76% Figure 2: Typical combined water use recovery system 52 June 2019 www.cibsejournal.com CIBSE Jun19 pp50-52 Cooling Tower.indd 52 24/05/2019 16:57