DOMESTIC HOT WATER SYSTEMS | ECO-DUO PIPING Piping hot An innovative pipe-within-a-pipe design for domestic hot water systems offers improved energy efficiency and healthy and safe water for end users. Phil Lattimore looks at benefits of the CIBSE Award-winning Water Kinetics Eco-Duo A 45_degree elbow tting showing the pipe within a pipe T he provision and selection of heat generation for domestic hot water (DHW) systems is a vital element of any energy-efcient solution. At the CIBSE Building Performance Awards, the winner of the Product or Innovation of the Year Wellbeing category was the Water Kinetics Eco-Duo, which is designed to ensure energy-efcient, safe DHW supply that doesnt compromise consumer requirements. Eco-Duo is a copper pipe-within-a-pipe recirculation system that keeps hot water hot and cold water cold. It is designed to control the spread of water-borne pathogens and biolm, while still being highly energy efcient. The awards judges described the system as a novel, innovative product that addresses a real-life challenge robustly. Health and safety Health and safety are key issues when it comes to DHW supply. Hot and cold water needs to be kept at the desired temperatures, and the water has to be kept moving on a regular basis. DHW systems in commercial and large residential buildings have long incorporated recirculation systems, where water is constantly reheated and pumped around the system to maintain a safe working temperature. The main safety issues for DHW systems involve the control of pathogens and prevention of scalding. Traditionally, potable water circulation comprises separate ow and return pipes, with branches off the ow pipe to individual outlets. The ow, return and branches are all subject to temperature loss, relative to the distance from, and return to, the heating source. Areas of low temperatures occur where there is no circulation in these branches during periods when outlets are not being used or used less frequently. This can result in the undesirable proliferation of pathogens, such as legionella bacteria. Combating these issues requires costly, time-consuming monitoring, treatment, and wasteful ushing regimes. The control of these pathogens is achieved by compliance with HSE Approved Code of Practice (ACOP) L8. It requires keeping water at a minimum of 60C and ensuring distributed water is supplied at 50C (55C in healthcare buildings) to outlets within one minute; the temperature in the return pipe must be at no less than 50C. This requires system sanitisation and/or chemical treatment to be deployed frequently. The most effective way to ensure that legionella bacteria is controlled involves raising water temperature to 70C. For this to be effective, it must include every outlet and section of pipework subject to heat loss. Raising temperatures, however, increases the risk of serious injury from scalding. Energy efficiency Reducing energy usage is an essential consideration for new or retrotted DHW systems. Heat loss in a conventional system is directly proportional to the difference between the water temperature and the temperature of the air surrounding the pipe; in a conventional system, this will be from both the ow and return pipes. Water in the system must be constantly reheated and pumped around the system. Reducing heat loss from the surface area of the pipework could, therefore, signicantly increase thermal efciency. In addition, where storage is necessary to satisfy uctuating patterns of DHW demand, current legislation (HSE HSG274) requires water be kept at or above 60C. This in turn requires a constantly high amount of energy. The pipe within a pipe To address these issues, the Water Kinetics Eco-Duo circulation system incorporates a coaxially congured return pipe within the ow pipe, reducing surface area and heat loss. Water Kinetics says this approach can halve installation time and costs, pipe 38 May 2022 www.cibsejournal.com CIBSE May 22 pp38-39 Water Kinetics.indd 38 22/04/2022 18:08