Taking control of cold water
Storing cold water might be regarded a one of the simplest services in a building — but there are a number of operational and safety issues — as Neil Weston of Keraflo explains.
Within commercial buildings, domestic water is a requirement, which is regulated by The Water Supply (Water Fittings) Regulations 1999 (upheld by WRAS). Water is necessary for hygiene purposes such as washing and cleaning, for emergency reasons such as fire control and for drinking. Since significant amounts of water are consumed in these types of buildings, it is essential to ensure that an adequate recommended level of water is stored through the use of a cold-water storage tank.
It is important to bear in mind the building’s requirements in terms of the size of the tank needed to maintain a good supply of water. CIBSE Guide G (2004) Public Health Engineering provides accurate data on calculating water-storage requirements for various buildings by taking into account the type of building, its size, occupancy and use. In many cases, the size of a water tank presents a real challenge —especially for a building requiring a large amount of water to be stored onsite.
|Not only does a delayed-action float valve enable a tank to be filled to a greater depth than an equilibrium valve, but it is also either fully open or fully closed — avoiding the problems association with water trickling into the tank.|
The use of an equilibrium valve [float valve] can significantly reduce the tank capacity.
For example a 1 m3 tank, with a nominal capacity of 1000 l in actuality only ever holds about 500 to 600 l when it is full. It is therefore essential to optimise the tank size with the nominal water capacity, to ensure that the highest volume of water can be stored. Unfortunately, to achieve this, installers have often opted for solutions that do not comply with WRAS, such as using a drop arm with an equilibrium valve in a raised chamber. This creates a system with too many variables at work, relying on a number of mechanical joints — producing weak points that increase the risk of failure and having the potential to be unreliable.
A compliant option would be to install a delayed-action float valve. This solution can increase the tank’s nominal capacity to around 80%, ensuring the most effective and efficient cold-water storage management solution.
It is also important to ensure that water is clean and safe for all to use. When water is allowed to just trickle into the storage tank, there is more chance for waterborne bacteria such as legionella to breed. This situation can be avoided by using a delayed-action valve. The valve’s quick mechanism, where it opens and closes at speed, provides a full-flow and full-bore action, which aids water turnover and agitation, helping to prevent stagnation.
For even more control, a fully integrated tank-management system (such as Tanktronic from Keraflo) can provide accurate readings on water depth and temperature delivered via a user-friendly interface. An alarm function can be programmed to inform the user if the volume or temperature of the stored water exceed set criteria, allowing action to be taken before a problem escalates into a crisis.
With the use of a cold-water storage tank comes the concern of backflow — an unwanted flow of water in the reverse direction, potentially resulting in system contamination. The technique preferred by the UK Water Authorities to prevent any form of backflow, is to utilise an air-gap of the correct type for the application.
With the use of an air gap, if a vacuum should occur in the supply pipe, air will be drawn in rather than water, which eliminates the risk of water contamination from backflow. The Water Regulations stipulate the minimum vertical distance that should be provided between the outlet of the supply pipe and the stored water. This distance is sized on twice the bore of the incoming feed pipe; the minimum height is 20 mm.
Cold-water storage is paramount within commercial environments, yet with this comes a host of issues. Not considering and dealing with these issues could result in serious implications, not only in terms of health to users, which could include members of the public, but also in terms of the associated costs and inconvenience in rectifying problems. It is important that the issues are considered during the design stage and that end users and those responsible for the facility in question are made aware of these possible concerns and how these problems can be overcome.
Neil Weston is sales manager with Keraflo.