Domestic Hot Water (DHW) - Entorn Urbà i Salut

Equipments

Domestic Hot Water (DHW)

CONTEXT

When it is necessary to have a domestic hot water (DHW) installation with an accu-mulator in a facility, even though not everyone may need it, it is extremely important to take into account that such installations should be meticulously designed and maintained in order to ensure they do not become hot spots for the Legionella pneumophila bacterium, which causes Legionnaires’ disease.

Legionella is an environmental bacterium whose natural ecological niche is surface water. From its natural habitats, this bacterium is capable of colonising the water supply systems of cities. It is capable of surviving broad spectrums of physical and chemical conditions. It multiplies between 20 and 45 ºC, grows from 35 to 37 ºC, and only dies at temperatures in excess of 70 ºC. For this reason, once present in DHW systems that are poorly designed and/or poorly maintained, Legionella may proliferate, disperse and infect human beings. Installations of a certain size are normally designed to include an accumulator and a water return circuit. Such installations are considered to have a high risk of transmitting Legionnaires’ disease.

OBJECTIVE

• Prevent the development of Legionella by properly designing and maintaining DHW installations.

PROPOSALS AND RECOMMENDATIONS

• Guarantee, by means of the effective management of maintenance actions that the temperature of the accumulators in a DHW system does not fall below 60º C so that it does not favour the proliferation of Legionella, as established in Royal Decree 865/2003.
• Periodically maintain and/or clean DHW systems to prevent and/or reduce the formation of incrustations and corrosion in heat exchangers and accumulators, where Legionella is prone to accumulate.
• Choose exterior heat exchangers for the installations.
• Accumulators with a capacity in excess of 750 l must have a manhole with a mini-mum diameter of 400 mm that is easily accessible and free of obstacles, allowing access to the tank to perform inspection, cleaning, disinfection, maintenance and corrosion prevention operations. Tanks with a volume of less than 750 l must be equipped with a means of access commensurate with their size, unless they are double tanks.
• Choose suitable materials for the pipes of the DHW circuits, respecting the characteristics and compositions of the local water and the temperature at which it is to be used in the facility. Avoid materials that favour the develop of bacteria and fungi, such as leather, wood, fibre cement, concrete and cellulose derivatives, as stated in Royal Decree 865/2003.
• Design DHW installations in accordance with the Building Thermal Installations Regulations (RITE) in terms of their materials, disassembly facility, drainage facility, pipes, and the thermal insulation of the entire DWH system.
• There is the option of designing the domestic hot water production system in such a way that it accumulates water in the primary circuit. This approach reduces the number of Legionella proliferation risk points and the accumulator does not have to be subjected to Legionnaires’ disease preventive maintenance and control operations.
• Include manholes in new installations and in renovations to enable the cleaning, disinfection and maintenance of DHW systems.
• Include a Legionella prevention protocol (heat shock) in the building maintenance record and automate it by means of programmable logic controllers, in such a way that the disinfection of the installation is automatically carried out in the stipulated sequences.
• Implement an exhaustive maintenance programme as per the requirements of Royal Decree 865/2003, carrying out checks, cleaning, disinfection and tempera-ture controls in accordance with the various types of DHW installations, always through authorised companies.
• Annually assess the action programme as established in UNE standard 10030:2017 through a duly qualified and experienced technical team, whose members must have completed an official course on the hygienic and sanitary maintenance of installations with a risk of spreading Legionnaires’ disease.

REFERENCE EXPERIENCES

LEGISLATION

• Reial Decret 865/2003, de 4 de juliol, pel qual s'estableixen els criteris HIGI-énico-sanitaris per a la prevenció i control de la legionel·losi.
• Decret 352/2004, de 27 de juliol, paper qual s'estableixen els condiciones higienicosanitàries per a la prevenció i el control de la legionel·losi.
• Reial Decret 830/2010, de 25 de juny, pel qual s'estableix la normativa reguladora de la capacitació per realitzar tractaments amb biocides.
• UNE 100030: 2017 Prevenció i control de la proliferació de legionel·la en instal·lacions.

STUDIES AND TECHNICAL DOCUMENTATION

• ANECPLA. "Plan de Prevención y control de legionelosis para sistemas de Agua Fría para el consumo humano".
• ANECPLA. "Plan de Prevención y control de legionelosis para sistemas de Agua Caliente Sanitaria".
• ANECPLA. "Guía para la contratación de Servicios de Prevención y Control de Legionela".
• Servei de Salut Pública de la Diputació de Barcelona, 2013. "Criteris par a l'avaluació de les bones pràctiques en instal·lacions amb risc de proliferació de legionel·la".
• Ministerio de Sanidad, Consumo y Bienestar Social. Guía técnica para la prevención y control de la legionelosis en instalaciones.
• Norma UNE 100030, abril 2017. Prevenció i control de la proliferació i disseminació de legionel·la en instal·lacions.

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