The Building Conservation Directory 2020

147 C AT H E D R A L C O MM U N I C AT I O N S T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 2 0 HEATING & LIGHTING SERVICES 4.2 to be more cost-effective ways of reducing the building’s environmental impacts. Maintenance Most water recycling systems require some level of maintenance. The British Code of Practice for Rainwater Harvesting systems, BS 8515, provides guidance on this, but the key points are to check for blockages, correct operation of mechanical and electrical parts, leaks, and the condition of filters. Given the parts lists of even a modest water recycling system, there are lots of opportunities for failure. Many systems incorporate some sort of mains- fed backup, and the Environment Agency’s report shows that it is not uncommon for failures to remain undetected, reverting the building to 100 per cent mains water. The reality is that for most ‘normal’ buildings, it’s simply more environmentally friendly and economical to flush away mains drinking water than to capture, treat, store and pump rain or grey water. CONSERVATION: SIP, DON’T GULP Before splashing out on a rain or grey water recycling system, it is worth considering what can be done to reduce consumption. This can be often be done more cost-effectively through simple retrofits, upgrades or design changes, or at almost zero cost, by the occupants implementing behaviour changing measures like taking shorter showers. Selecting smaller baths, dual flush WCs, flow-regulators and aerating taps and shower heads also form a key part of this approach, but ideally this should be coupled with careful system design to avoid unnecessary dead-leg volume and minimise the wait for hot water to arrive. Happily, consumer demand, Enhanced Capital Allowances and the application of Part G and the Code for Sustainable Homes has driven development of useful water saving technologies in the last 10 to 20 years, and there is now a good selection of water saving equipment for both new build and retrofit applications. Dual-flush WCs are all but standard today, and often cisterns can be retrofitted with a dual-flush. Many of these ideas can be incorporated into an existing building easily and inexpensively. A wholesale re-plumb will always present more opportunities to improve water and energy efficiency, but there is a great deal of low-hanging fruit not requiring such dramatic interventions. Part G of the building regulations provide a legal minimum performance standard, but some would argue the water consumption calculation is somewhat arbitrary and open to abuse. The Association for Environment Conscious Building (AECB) Water Standards is an excellent reference point to use, with plenty of technical background. It promotes the control of flow rates at each outlet, which is simple and inexpensive to achieve via either flow-regulating tap aerators, or regulating valves provided to each outlet. Reducing the water consumption of a building through good design and specification, as well as behaviour change, has multiple benefits. As well as reducing water stress and greenhouse gas emissions associated with the water, it reduces the energy required to heat water, and if a recycling system must be used, it can be reduced in size and cost. Direct and indirect rainwater harvesting systems (All diagrams: Toby Cambray) A detail of a typical map issued by the Environment Agency showing water body stress levels in the South East. old building just to install such systems. All this assumes the water is not to be rendered potable, which is significantly more demanding in terms of treatment; the necessary filtration and sterilisation is possible, but relatively complicated, involving finer filtration and possibly the addition of chemicals and UV lamps. The gravity of the situation A 2010 report from the Environment Agency found that although there is scope to reduce the carbon footprint of grey and rainwater harvesting systems, ‘buildings using harvested rainwater or treated grey water typically increase greenhouse gas emissions compared to using mains water,’ when lifecycle impacts are accounted for. The operation of the electric pump is always one of the biggest, contributors to the lifetime footprint. A highly efficient circulation pump might achieve over 40 per cent efficiency, but the small submersible pumps used in recycling systems might be as low as 15 per cent. In many cases, below ground storage vessels must be encased in concrete to avoid buoyancy, in ground water. This greatly increases embodied energy and carbon. For larger, non-domestic buildings, systems can be more efficient, so there can be some energy and carbon benefits, but there are likely