Efficient solutions for small-scale hot water
Electric undersink water heaters such as Heatrae Sadia’s Multipoint provide a convenient means of serving several low-usage outlets such as washrooms.
If a building does not have sufficient demand for hot water to justify installing storage cylinders or investing in renewable systems like solar thermal, how can heating specifiers ensure that the hot-water delivery is as efficient as possible? Jon Cockburn suggests some options.Though all commercial and public sector buildings have a need for hot water, the degree required can vary quite significantly. Hot-water systems in some buildings will serve a large number of showers, sinks, washbasins and even baths — for example those installed in leisure centres, hotels, university halls of residence, schools, care homes and prisons. On the other hand, a large proportion of buildings will need just a few sinks and washbasins — such as offices, doctors’ surgeries, dental practices, hairdressing salons, factories, supermarkets, pubs, shopping centres and restaurants. With the energy efficiency of commercial and public sector buildings being extensively scrutinised, this hot water must be delivered in an efficient manner. At present, solar thermal water heating is seen as the ideal renewable solution, with the Sun’s free energy being able to provide a significant proportion of a building’s hot-water demands. However, solar thermal water heating requires a fairly large hot water store, and it is not always viable, cost effective or energy efficient if the demand for hot water is low. So, how do building managers and specifiers ensure that small-scale hot water delivery is energy efficient? When there is a requirement for just a small number of people to wash their hands and perhaps do a small amount of washing up (which could be the case in many applications like small offices and doctors’ surgeries), point-of-use water heaters can provide a hygienic, efficient and cost effective solution. Generally sited next to the point they serve, single point-of-use storage water heaters provide hot water to a single sink or basin, and are typically available as oversink or undersink units. Being close to the point of use, they can be fed directly from the cold-water supply, eliminating the need for a hot-water supply from a remote boiler. They are a relatively low-cost option and are simple to install, but it must be remembered that undersink water heaters need a purpose-designed vented tap. Heating water close to the point of use can reduce energy consumption and water usage. Standing heat losses in the supply pipework are minimised, and users will not have to waste large amounts of cold water whilst waiting for the water to run hot. Some point-of-use systems operate on a displacement principle; they have an open outlet and rely on the opening of a tap or valve on the inlet side to displace the hot water in the heater with incoming cold water. Opening the valve forces hot water out by displacement, and the open outlet ensures any excess pressure in the heater is vented. Electric instantaneous hand-wash units also offer an economical and energy efficient supply of hot water to serve one sink or basin — and also heat water at the point of use. Typically used in small washrooms, these units are usually compact and slim line in design, so require just a little wall space. They have a swivel spray outlet attached to the unit and are turned off and on with a switch or dial. Automatic versions are also available, which provide a set amount of hot water (for example 25 seconds) delivered at a preset temperature.
Though some commercial and public-sector buildings need only a small amount of hot water, they might still want the powerful hot-water performance that a larger system would provide. For example, a stylish restaurant or bar or a hairdressing salon could benefit from having powerful hot water because it might make a positive impression on customers. In these circumstances a small unvented system would be an ideal solution. Fed directly from the cold water mains, unvented systems provide powerful hot water without a loss of performance if more than one tap is used simultaneously. Unvented systems are quite commonly installed in domestic dwellings, where large unvented cylinders are used to serve multiple bathrooms. However, lower capacity (small unvented) versions can satisfy the hot-water requirements of washrooms in commercial and public sector premises where multiple sinks and basins are in use. As well as delivering powerful hot water, small unvented water heating units can be more cost effective to install than single-sink open-outlet water heaters. In larger buildings, a number of small unvented water heaters can provide a more flexible design solution than one large centrally distributed hot-water system, allowing individual units to be isolated or serviced without closing down a building’s complete hot-water supply. Small unvented hot-water storage units can include thermostatic blending valves (TMVs), which allow water to be stored at a high enough temperature to eliminate bacteria, yet dispense it at a ‘safe’ pre-set hand-wash temperature. Storing water at a higher temperature also increases the amount of usable hot water available at the tap. Heatrae Sadia manufactures a range of small unvented systems suitable for commercial applications, which are designed with ease of installation in mind. Suitable for multi-basin supply, Hotflo (in 10 and 15 litre capacities) is ideal for a range of light duty commercial applications, while the Multipoint range (available in 10, 15, 30 and 50, 75 and 100 litre capacities) is designed for applications with a higher demand for hot water or can serve a larger number of lower usage outlets. The 75 and 100 litre Multipoint models have a rectangular profile and a similar footprint to cistern-type water heaters, so are an ideal replacement product when improved flow rates are required. In recent years there has been a lot of focus on improving the energy efficiency of water heating in commercial buildings, and the use of renewable technologies like solar thermal has been widely discussed. However, for applications with a smaller demand for water heating, point of use and small unvented products can provide efficient, hygienic and cost effective solutions. Jon Cockburn is marketing manager with Heatrae Sadia.
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