Gerry Quinn looks at the specification options and installation issues surrounding rainwater harvesting technology
Our Victorian forefathers dispensed with the ancient practice of collecting rainwater more than 100 years ago, following the introduction of piped mains water supplies into their homes.
Fast-forward to 2009 and this cost-effective and simple technology is enjoying something of a resurgence.
Indeed, it is entirely feasible even in the current climate to suggest that, within four to five years, perhaps 75% of new-builds could have some form of water reuse system installed.
There are a number of industry initiatives and other drivers that are supporting the use of this cost-effective and simple technology.
Perhaps the most pertinent for m&e contractors and consultants is the ever-growing application and importance of the Building Research Establishment Environmental Assessment Method (BREEAM), which is designed to recognise the environmental performance of a building through a scale rating. Every available point needs to be secured to reach an excellent standard, so rainwater harvesting equipment, which is given points in a couple of categories, will often be installed.
Most new-build schools, colleges, offices, government buildings, multi-residential and retail buildings should now be designed to meet a high BREEAM rating.
Rainwater harvesting systems
The operating principles for different rainwater harvesting equipment across the UK are broadly the same.
Once the rainwater has been collected from the roof of the building, usually via the guttering, it is filtered before entering either an above or below-ground rainwater holding tank. Holding tank sizes will be dictated either by the calculation method shown in the British Standard BS 8515, or in line with the BREEAM requirement pertinent to the project.
The mechanical aspect of the project is then designed to meet the requirements of the building on a site-specific basis.
While there are a number of options available, the system can broadly be configured in one of three ways.
This system is designed to pump the collected rainwater from the main holding tank to a high-level header or break tank within the building. The header/break tank will then service the non-potable appliances as per normal.
Mains water back-up is also delivered to the header/break tank, independently of rainwater, but these systems are configured to introduce mains water only if rainwater supplies are exhausted or if electrical power to the building/rainwater harvesting system is interrupted.
Assuming that a high-level header/break tank can be installed, this would generally be the preferred option.
If a header/break tank is not suitable in a modern building, an alternative arrangement may be required.
In a direct system, the rainwater is delivered directly from the main holding tank to the point of use. In this instance, and following water regulation requirements, the mains water back-up would be directed straight into the main holding tank.
Booster systems are a combination of both gravity and direct systems.
Here, the collected rainwater is delivered from the main holding tank to a surface-mounted break tank and booster system. This option gives the combined benefits of both the direct system – particularly useful in larger applications – and the gravity system, in that the mains water back-up is directed to the break tank.
You will be glad to know that installation should be a simple task for the competent mechanical and electrical contractor. Most rainwater harvesting systems come supplied with all the non-standard, specialist parts supplied in the package, and any other required components are industry-standard fittings and pipework.
In order to ensure that all trades involved with the installation are fully briefed, from groundworks through to final commissioning, we recommend having an on-site, pre-installation consultation. Check with your supplier, but this is something that comes as standard (and free of charge) with KingspanWater equipment.
You should also be aware that rainwater harvesting equipment brings with it new levels of Water Regulations requirements that are vital to protect the public water supply.
For further information and advice, we recommend going to the Water Regulations Advisory Service (WRAS) website (www.wras.co.uk).
Many of the regulations revolve around two principal requirements for rainwater harvesting equipment to comply with:
- Colour coding and marking of pipework and appliances using the reclaimed water supply.
- The requirement for an air gap in the system to separate the reclaimed and mains water supplies, thus ensuring the avoidance of cross-contamination between the two systems.
As more and more systems come onto the market, there is a pressing need to instil early confidence in the sector, both around the technology and the quality of the resulting water.
Achieving this requires the application of British Standards, and KingspanWater technical director Mike Norton, chair of the UK Rainwater Harvesting Association, has devoted considerable time over the past 12 months to instigating, and helping draft, a Standard for rainwater harvesting equipment.
The result, BS 8515 for Rainwater Harvesting, was published in January.
Its aim is to comfort planners, specifiers and consumers, as well as ensure compliance by suppliers to minimum standards. It also addresses any concerns about the possibility of cross-contamination of mains drinking water with rainwater.
Mike is also calling for a national training programme that will ensure standards of installation are meeting minimum criteria. Anecdotal evidence seems to suggest many of the complaints that suppliers are fielding are not down to issues with design, but, instead, issues concerning poor or incomplete installation.
The aim of both the British Standards and the training programme is to ensure the untrained or uninitiated do not undermine trust in the sector before it is fully established.
Gerry Quinn is product manager of KingspanWater.
Defra’s Lion House low-water-use building set to be a roaring success
Lion House is an ultra-low-emissions office building, designed and built for the Department of Environment, Food and Rural Affairs (Defra), in Alnwick, Northumberland.
From the outset, the aim was to construct a building with the highest possible BREEAM rating. That included incorporating low-energy technologies, responsibly sourced materials and reduced carbon emissions.
Another aim was to minimise mains water consumption through fittings that had low water use and rainwater harvesting systems.
The project’s m&e contractor, Haden Young, approached Kingspan Environmental to design a suitable solution for the building.
The Kingspan Environmental team worked closely with Haden Young to configure its Envireau equipment to meet the water consumption requirements for toilet flushing for Lion House’s 100 employees.
The agreed system comprises a pre-tank filtration system, a 12 000 litre underground storage tank, an electronic control system and a pump. The pump in the main holding tank delivers the water to a high-level header tank in the building, from where the water will gravity-flow to the serviced appliances.
The team calculated that the annual water consumption at Lion House would be around 469 m3.
Given the roof area of the new building and given also the annual rainfall statistics for the region, it was estimated that the annual water harvest would be around 563 m3.
In theory, therefore, all the annual toilet-flushing water requirements would be expected to come through the rainwater harvesting system.
Gerry Quinn, product manager for KingspanWater, says: “Reusing rainwater presents savings not just for the environment, but also in terms of reduced water rates.
“At today’s water costs, we expect to see Lion House saving in the region of £800 per annum, so we would anticipate payback on capital investment in around four to five years’ time.”
Client: Defra Estates Division
Contractor: Kier Northern
Building services: Haden Young/ Faber Maunsell
Structural engineer: Faber Maunsell
Project management: Appleyards
Electrical and Mechanical Contractor
For more information, call the KingspanWater Technical Advisory Service on 01296 633139, or visit www.kingspanwater.com