With increasing environmental pressures and an overwhelming drive to reduce the use of fossil fuels, there has been a large increase in the use of solar energy to heat domestic hot water. This is a trend set to continue with EU targets requiring 20% of all energy to be renewable by 2020. However, concerns have been raised as to whether an increase in the use of solar heating will put more people at risk from Legionella bacteria. It appears there is a potential problem with both design and operating characteristics of solar heating systems. A number of systems on offer are ‘twin coil’, that is the hot water cylinder contains two coils; one containing water from the solar panels and one from the central heating boiler. The solar coil is usually positioned at the bottom of the cylinder and used to heat the ‘dedicated solar volume’ – the volume of water that can only be heated by the solar input. With a cylinder designed as above there are a number of problems; 1. There is no guarantee that the water at the bottom of the cylinder (where the cold enters) will be heated to 60 degrees all year round 2. In a large number of cylinders it is not possible to ‘heat to base’ – i.e. the entire contents of the cylinder cannot be heated to the 60 degrees as required in ACOP L8. 3. Additional water storage (to account for dedicated solar volume) can lead to turnover exceeding 24 hours, with most calculations this is more like 2 days. With the majority of Legionella Management strategies centering on maintenance of a strict temperature regime it is thought the above could have a measurable impact. Manufacturers, who have a design duty under L8, are already onto this and some have even offered upgrades to systems already installed. It is essential that any system falling under L8 are risk assessed properly, on a design specific basis and taking into account the operating characteristics. Even where anti Legionella precautions are built in it is still crucial that they are operated as intended by the manufacturer. For more information visit www.nemco-utilities.co.uk or call the office on 01284 724503. Contact Details: Nemco Utilities Ltd 12 Hillside Road Bury St Edmunds Suffolk IP32 7EA Telephone: 01284 724503 Fax No.: 01284 724826