56 HPM 0816

HPM-08-AUG-2016

56 SUSTA I N A B I L I T Y & WAT E R S AV I N G Storming ahead with rainwater harvesting Rainwater harvesting is a growth market for plumbing installers. Kevin Reed, of Graf UK, looks at the increasing trend for combining this with sustainable urban drainage systems and In the UK, one third of the explains what installers need to know to respond to rising demand domestic water we use is for jobs like flushing toilets, watering gardens and washing clothes and cars and subsequently does not need to be of drinking quality. Rainwater harvesting (RWH) systems provide a straightforward and sustainable way to collect and repurpose rainwater for a variety of domestic and commercial applications. As such, they have been growing in popularity. The need is particularly strong in densely populated parts of the UK with lower rainfall such as London and the south east. In fact, water companies in these areas and beyond are actively encouraging consumer investment in RWH as a way to reduce pressure on the potable mains water supply. All of this is having a positive impact on market growth, but it doesn’t stop there. In stark contrast to the risk of water shortages and droughts, the increasing threat posed by serious flooding is causing a surge in demand for solutions that can cope with both weather extremes. As a result, the spotlight is now on RWH systems that can be combined with sustainable urban drainage systems (SuDS). This combination represents a lucrative opportunity for installers, but to make the most of it, they need to understand the market and the products on offer. It’s important to have a good grasp of the different RWH options available and in which applications they deliver best results. There are three main types to get to grips with: 1. Direct: Direct systems work by collecting water in an underground storage tank and pumping it directly to the points of use. They typically feature a controller, which detects when the water is needed, for example, when taps are turned on, or when the valves on washing machines and toilets are opened. This triggers the pump to supply water directly to the appliance. In some systems, this pump is submersed in the tank, whereas in others, such as, it is built into the controls unit inside the house, garage or plant room, which means the technology is kept dry. 2. Indirect: These work by collecting water in an underground storage tank, pumping it to a header tank and then gravity-feeding it to the points of use. They have much simpler (if any) controls than direct systems, with the submersible pump detecting when the valve in the header tank opens, and simply pumping water until it closes again. Valves in indirect systems are generally set so that they only open after three or four flushes of a toilet, for example, meaning that the pump is in use much less than in a direct system. In the case of a power failure, the system will automatically switch to mains water when water levels fall below a certain point in the tank. This added benefit works using a simple ball valve. 3. Gravity-fed: Above-ground, gravity-fed tanks are the most energy efficient RWH option. They can range from water butts, ideal for small-scale garden watering, to larger tanks, where water is required for a wider range of domestic or commercial uses. However, the latter are not suitable for all buildings, as they require significant roof space. Even where this space is available, substantial structural support is often needed to bear the weight of the water safely, which can incur extra costs. For these reasons, we always recommend using underground tanks where possible. When specifying, designing and sizing any RWH system, it’s crucial to consider what the water is going to be used for, as this will help you calculate the required demand. Once you’re familiar with the full scope of RWH options, the next step is to understand how these can be bolstered to provide effective SuDS alongside their harvesting capabilities. Stormwater management solutions represent a significant chunk of our business. This is no surprise given that all new developments are now obliged to calculate their flood risk and incorporate SuDS to minimise it. RWH cannot replace an entire SuDS system, but when combined with a stormwater management solution, you effectively get two systems in one – making both more cost effective. There are two methods of stormwater management: attenuation (where water is retained and then slowly discharged into the surface water drainage system or water courses) and infiltration (where water is gradually released back into natural groundwater reserves). While both can be combined with RWH, combination with attenuation is far more common in the UK. This is partly due to the clay-heavy soil in many areas of the country, which is not suitable for infiltration. Attenuation can usually be incorporated into the same tank as the RWH system, allowing for a one-tank solution, while infiltration generally requires a separate system. Small-scale attenuation: In the case of an individual domestic property, an oversized RWH tank can be designed to incorporate attenuation. This means setting the outlet high enough to provide the correct volume of water for reuse in the bottom of the tank, but low enough to ensure sufficient space for attenuation at the top. The water above the outlet is released at a controlled rate. This reduces pressure on the surface water drains and water courses during storms by spreading the discharge over a much longer period. Large-scale attenuation: On a larger scale, forexample, for housing developments or commercial premises, tanks can be made from modular cells, wrapped in an LLDPE-welded membrane. The top part is then used for attenuation, with the remainder retained for reuse. Infiltration: Stormwater infiltration can be incorporated into a RWH system by adding a crate-style soakaway. This method is only suitable for parts of the country with the right soil type, for example, not clay- or rock-based. As climate change makes floods and droughts increasingly common, the strong commercial prospects for installers working with rainwater harvesting systems are clear. Those who take this one step further by familiarising themselves with combinable RWH and SuDS solutions will be in pole position to maximise this opportunity even further. www.hpmmag.com August 2016 enquiry number 139 Indirect RWH system RWH with stormwater attenuation Direct RWH system RWH with stormwater infiltration


HPM-08-AUG-2016
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