WATER CONTAMINATION LEGIONELLOSIS BIG
CLEAN-UP C
Are tests for deadly bacteria in water systems a help or a hindrance, and what can be learnt from the American experience? Ewen Rose reports on the questions posed at an international CIBSE/ASHRAE webinar
oncerns over growing threats of contamination in water heating systems have been aired by experts in the field.
Simon French, a legionella expert from the Heating and Ventilating Contractors’ Association (HVCA), told a recent webinar that European countries had been trying to establish a robust system of risk assessments that provide control measures based on log books and auditing. ‘We have been at it for years, but we
still walk into buildings all the time that have never had a risk assessment. The issue is who actually polices the system,’ French told a recent webinar conference on legionella, organised by the CIBSE/ ASHRAE Group and hosted by University College London. The growing market for solar thermal
water heating has also increased fears that legionella – the bacteria that causes forms of pneumonia such as Legionnaires’ disease – will proliferate in systems because of water being stored at temperatures in the ‘danger zone’, French said. As a result, many indirect hot water systems and renewable pre-heat cylinders need regular pasteurisation as a precautionary measure. This is a highly energy intensive process and building owners are keen to find
46 CIBSE Journal February 2012
alternatives because of rising energy costs, he added. David Pepper, managing director of
manufacturer Lochinvar, which supported the webinar, said there was an argument for completely reversing the conventional solar water heating process to eliminate the risks posed by stored hot water. ‘It is now possible to engineer a system
where the pre-heated water from a solar thermal system is not the same water as that which is distributed at the hot water draw-off points,’ said Pepper. ‘This is achieved by transferring heat from the thermal store to the stainless steel indirect coil, which is then used as feed water for a traditional water heater.’ Robert McLeod-Smith, chairman of
the UK’s Legionella Control Association, confirmed that there had been wide discrepancies in test results from water samples and that this had made the job of legionella control specialists more difficult. However, he added that it was an important way of establishing that legionella was at least present in a water system. Bill McCoy, who chaired the ASHRAE committee on the proposed new American Standard 188P on preventing legionellosis (the term used to cover the group of diseases caused by legionella bacteria) said:
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