COOLING TOWERS | WATER CONSERVATION TOWERING SAVINGS Big cuts in building water consumption can be achieved by using non-potable water in cooling towers, says Hilson Morans Andrew Russell, who considers what water treatment solutions make the best savings W ater consumption is a major consideration in large commercial buildings and, with world resources of drinking water at a premium, the need to look further to explore possible solutions for water conservation are much needed. In recent years, the use of water by building occupants has been the focus, with improved design standards leading to more efficient water fittings and improved system design. Water-recovery systems have also received attention lately, leading to more buildings incorporating rainwater and greywater recovery systems. However, the water consumed by building cooling systems has largely been ignored, relying on designers perceptions of good practice to arrive at suitable and, hopefully, efficient solutions. The water make-up use for cooling towers (CT) often has been overlooked with large volumes of potable water being wasted. The main focus of this article is to show how a more sustainable solution can reduce potable water consumption and achieve additional credits for efficient water use within the project environmental assessments. Most water-based efficiency measures can be analysed relatively simply and in isolation. This is not the case for CT water consumption, where a number of interrelated factors need to be considered to establish optimum solutions. These include the combined effect of other water-recovery systems, the capital costs of cooling equipment and associated water-treatment systems, and the economic life of each system including consequential operating costs. By analysing these competing considerations holistically, an optimal solution can be achieved. Condensate recovery Greywater harvesting Rainwater harvesting Chemical water treatment Cooling towers Side stream electron magnetic treatment Reverse osmosis treatment Ozone treatment UV water treatment The water treatment options considered here include a number of water-treatment processes, which are widely used in the industry and have been considered for efficient treatment of the CT make-up water. They are: 1. Chemically treated CT with reverse osmosis (RO) treatment 2. Chemically treated CT with packaged side stream and membrane filtration treatment 3. Chemically treated CT with side stream separator and electromagnetic (EM) pre-treatment 4. Ozone treated CT 5. Ozone treated CT with RO pre-treatment. A notional building with a fixed heat rejection load was used to allow analysis and comparison of the water savings with these solutions. The notional building is very representative of many new large commercial developments currently being constructed, where CTs 50 June 2019 www.cibsejournal.com CIBSE Jun19 pp50-52 Cooling Tower.indd 50 24/05/2019 16:56