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Diluting Demand
July 7, 2011
Best Practice Target for Water Use Could Deliver Savings
By Jon Morton
Commercial office buildings in Canada are large consumers of water – using 19% of the total municipal water supply. The heating, ventilation and air conditioning (HVAC) system is the largest user of water in a typical commercial building, largely due to the operation of cooling towers. Other main sources of water consumption in commercial buildings are domestic use for toilets/sinks and irrigation/landscaping.
A best practice range for water use would provide owners and managers with a tool to evaluate their buildings’ water performance. In an effort to peg that range, researchers recently looked at buildings participating in the Canada Green Building Council’s (CaGBC) national GREEN UP program, drawing data from 74 buildings that reported water consumption information in 2009.
Water consumption intensity is measured in litres per square foot per year (L/ft2/yr) since analysis indicates that consumption correlates more strongly with building area than occupancy. Data for 2009 can be categorized by two predominant geographical regions, creating subsets of 20 buildings in western Canada (Manitoba, Saskatchewan, Alberta and British Columbia) and 50 buildings in Ontario.
The two regions were in sync at the 75th percentile with consumption intensities of 125 L/ft2/yr. However, the median and 25th percentile for the western provinces, at 60 L/ft2/yr and 38 L/ft2/yr, are lower than Ontario’s median and 25th percentile performance at 92 L/ft2/yr and 68 L/ft2/yr.
Across the entire sample, a larger proportion of buildings recorded consumption intensities between 45 and 135 L/ft2/yr with relatively fewer buildings recording intensities in excess of 200 L/ft2/yr. Buildings roughly falling into the best-performing quartile give rise to the recommended best practice range of 12 to 50 L/ft2/yr.
That range is largely equivalent to the NABERS (National Australia Built Environment Rating System) 5-star rating and encompasses the UK Watermark benchmarks for best practice in office buildings in the United Kingdom. It also conforms with known industry performance cited in various corporate responsibility and sustainability (CSR) reports.
If all buildings in the dataset performed at the upper end 50 L/ft2/yr, water savings of 2.5 billion litres are projected. Saving water also indirectly reduces greenhouse gas (GHG) emissions since treating and pumping water consumes energy.
COOLING, WASHROOMS & LANDSCAPING
There is an important distinction between water efficiency and water conservation. Water efficiency mainly refers to technological improvements (e.g. performance of water fixtures), where less water usage results without a loss in service level or performance. Water conservation, on the other hand, is related to the amount of water consumed by the end user.
To be sure, water efficiency is simply one form of water conservation. Water conservation generally encompasses any effort, through a myriad of ways, to reduce the amount of water used in an activity or process.
Offices are substantial water consumers, chiefly from the operation of cooling towers and domestic washroom and sink use. Office buildings need to provide cooling to remove heat that is present from computers, lights, people and other activities that take place in the building. Both cooling towers and domestic use offer opportunities for water consumption reductions through efficiency improvements and/other conservation measures, but this does not necessarily mean having to replace equipment.
Reductions in cooling tower water consumption can be achieved though improving the efficiency of the system, either by operating to specification and/or by reducing the demand on the cooling system in general. For example, by increasing a building’s temperature by a half degree Celsius during cooling months, the total demand for cooling is lowered. In a typical office building, reducing the cooling requirement by 10 tons of refrigeration can offer savings of up to 43,200 gallons of water per day.
Specific techniques to improve water consumption in cooling towers include:
● operating towers at a minimum of five cycles of concentration;
● avoiding once-through cooling; and
● providing related training to operators.
Better selection of mechanical systems used for cooling provides another opportunity for commercial buildings to conserve water. This is important for new construction and existing buildings – new buildings have the opportunity to consider the long-term savings of installing more energy and water-efficient equipment, while existing buildings have an opportunity to replace older, poor performing equipment in order to reduce operating costs.
Electric chillers typically carry the largest electrical consumption load in industrial, commercial and institutional buildings. As a result, retrofitting and specifying energy- efficient chillers and other HVAC equipment will have the most significant positive impact on energy and water consumption reductions in older structures.
Water-efficient fixtures are important to consider as their relative impact is significant to overall building water consumption. Nevertheless, education and promotion of water conservation is also required in buildings since the water efficiency improvements provided by these devices commonly can be defeated by inappropriate use by the consumer.
Landscaping provides another opportunity for lowering water use from existing levels. Established measures for water conservation include planting drought-tolerant plant species and grasses, as well as implementing watering programs based on weather patterns and rainfall rather than pre-set timing cycles.
EDUCATION & AUDITS
There are a number of conservation-oriented routes that building managers can choose in order to facilitate the reduction of water consumption. For example, tenants’ behaviour can be influenced through related educational and training offerings. These training offerings are often necessary to fully realize the benefits associated with more efficient domestic use and cooling water equipment and, ultimately, they help ensure the capital expenditures on equipment and fixture improvements are worth it.
Water audits can provide insight into a building’s consumption profile, and highlight those elements that are the worst contributors to high water consumption. Some would argue that for commercial buildings, water audits are critical to determining the water usage of all end-consumers within buildings.
When commissioning water audits, it is important for building managers to ensure that that the scope of the audit is accurately defined as measurement and estimation techniques can often vary significantly from company to company in audit reports. Typically, water audits should focus on policies for water conservation within the building as well as previous or ongoing water reduction efforts.
The preceding article is excerpted from Water Management: A Benchmark for Canadian Office Buildings, a study commissioned by the Real Property Association of Canada. The complete text can be found web site at www.realpac.ca
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