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Dr Jeremy Gibberd - SERA Building Indicators Group co-leader. |
The SERA Building Indicators Group (BIG) aims to develop a standardised and localised index for assessing the performance of green buildings in South Africa. In this issue of the SERA e-News, we feature a summary of the findings from a chapter of the 'Green Building Handbook for South Africa', in which BIG Team co-leader - Dr Jeremy Gibberd of the CSIR, describes water systems used in green buildings and sets out some objectives.
That clean water is becoming an increasingly scarce commodity is a fact. According to Gibberd, the development of green buildings systems is intended to minimise the consumption and pollution of this resource. Careful design is used to develop rainwater harvesting, plumbing and ecological sanitation systems that provide for water 'self reliant' buildings and that avoid water pollution. This reduces the requirement for large-scale water and sanitation infrastructure that consumes energy and can be very wasteful.
Water systems in green buildings differ in a number of ways from conventional buildings. Some differentiating characteristics are:
- Self sufficiency: Green buildings meet all or most of their water needs from rainwater harvesting.
- Water quality: The quality of water is matched with use. For instance, the best quality water may be used for drinking and cooking and poorer quality water, such as grey water, used for flushing toilets and irrigation.
- Onsite retention: In natural environments, vegetation and soil absorb and retain a large proportion of rain water. Green buildings emulate this by ensuring that buildings and sites absorb and retain rain water on site and avoid generating large quantities of run off.
- Evaporation and transpiration: Air can be cooled and the humidity increased through evaporation of water and transpiration from plants. This may be used in green buildings to improve comfort levels without the use of mechanical systems.
In addition to detailing some key performance objectives for water systems in green buildings, Gibberd also lists a number of calculations that can be used to design water efficient systems and rainwater harvesting systems for buildings. These include calculations for potential rainwater harvesting capacity; water consumption; grey water generation and consumption; and the sizing of rain water harvesting tanks.
According to him, there are also a number of aspects and components of water systems in buildings that can be used to ensure the achievement of green building objectives. One aspect is water meters which, in green buildings, should be located where they can be easily read in order to monitor consumption. In turn, sub-metering which allows water consumption to be closely monitored and controlled should be provided for areas with substantial water requirements such as large irrigation systems.
High water pressure is another consideration which can result in wastage with increased flow rates of taps and showers. Correct water pressures should therefore be specified in green buildings, with the use of pressure reducing valves if necessary.
In addition to the familiar issues of leaking taps and the water use of showers versus baths, Gibberd also explores the use of waterless toilets such as composting toilets and valve or chemical urinals. Other important considerations are described in the related chapter of 'Green Building Handbook for South Africa' such as planting techniques that minimise water requirements and the use of more efficient irrigation methods.
Additional aspects include grey water from showers and hand basins - proprietary and simple grey water systems can be used to reduce potable water consumption. Proprietary systems have sophisticated filters which sterilize water and remove sediment and dirt. Simple grey water systems may partially filter water and direct this to toilets for flushing or to landscape for irrigation.
Gibberd says that grey water from buildings can also be treated and filtered on site using reed beds and reused or allowed to replenish groundwater. This reduces the requirement for large-scale sanitation infrastructure and provides an additional source of water which can be used for irrigation. He contends that rainwater harvesting systems should be a central strategy in green buildings.
Through the use of the rainwater harvesting capacity calculations, he demonstrates that even in dry climates rain water harvesting can enable buildings to be totally self sufficient in water. The calculations also show that even relatively small rainwater tanks can make a significant contribution to reducing mains potable water consumption.
View Dr Gibberd's full chapter in the Green Buildings Handbook for South Africa.
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