Transcript
Legionella Risk
Important Information
for the Installer & House Owner of Domestic Hot Water Systems General information relating to legionella in all domestic hot water systems Property Address:
Installer Name: Installer Company: Installer Address: Date of Commissioning: Signed by Installer: •N ote –This document contains guidance for the safe operation of all domestic hot water systems. It is for guidance only and does not replace any National standards. •T his document should be completed and signed by the installer and left with the householder for future reference. Particular reference should be made to “National Guidelines for the Control of Legionellosis in Ireland, 2009” available from the HSE.he Scientific
Introduction – What is Legionella? Legionella bacteria are always present in water systems, but it is in large quantities that they can cause illness typically in the form of pneumonia. It can affect anybody, but some people are at higher risk including those over 45, smokers and heavy drinkers, those suffering from chronic respiratory or kidney disease, and people whose immune system is impaired. This type of pneumonia can be treated with special antibiotics. We usually associate legionella with larger water systems, eg in factories, hotels, hospitals and museums, and cooling towers, but they can also live in smaller water supply systems used in homes and other residential accommodation. Legionella can survive in low temperatures, but thrive at temperatures between 20˚C and 45˚C. High temperatures of 60˚C for 2mins will kill Legionella, in fact 50˚C for 2 hours will kill up to 90% of all Legionella present in a cylinder.
What should the installer do? Legionella bacteria can multiply in hot or cold water systems and storage tanks in residential properties, and then be spread, eg in spray from showers and taps. Although the generally high throughput and relatively low volume of water held in smaller water systems reduces the likelihood of the bacteria reaching dangerous concentrations, you must still carry out a risk assessment to identify and assess potential sources of exposure. You must then introduce a course of action to prevent or control any risk you have identified.
Assessing the risk It should be possible for you (the installer) to assess the risk yourself, but if you do not feel you have the right skills, you can obtain help and advice from a consultant. When you do the risk assessment the whole system must be considered, the following checklist will provide guidance in important areas, however all areas of the system (heating & hot water) should be investigated. The following checklist should be completed
Legionella Risk
System checklist This checklist has been created as an aid to help the installer of heating and domestic hot water systems in general in assessing legionella hazards within a domestic hot water system. This list is not an exhaustive list and we recommend national standards and guidelines be reviewed on a regular basis. There maybe hazards that have not been covered.
Checklist
Yes
No
Are conditions right for bacteria to multiply, e.g. is the temperature of the contents of the cylinder between 20°C and 45°C for extended periods of time? e.g. unoccupied properties Are there areas where stagnant water occurs (dead legs), e.g. pipes to a part of the building no longer used? Solution: Dead legs in pipework should always be avoided. Is there dirt or debris in the system, such as rust, sludge, scale? Typically found in old cylinders etc. Are there thermostatic mixing valves set at a favourable temperature for legionella growth? Solution: The min distribution temperature should be 60°C, therefore the min set temperature of the valve should be 60°C Is it likely that there will be no energy inputted into the tank for a long period. Solution: An auxiliary input (boiler/ immersion etc) should be supplying additional heat to the cylinder. This should be controlled by a thermostat on the cylinder which is fixed to a temperature of 65°C. The adjustment dial should be fixed to ensure accident adjustment is prevented. *note* A thermostatic mixing valve must be installed on the system to prevent scolding. Is the building other then a domestic house? i.e. nursing home, hospital, hotel, leisure centre etc. Solution: Contact our technical support office @ +44 2838364500 for advice on correct design solutions. Are there long periods of no usage of the hot water supply without auxiliary backup heating? i.e. holiday homes. Solution: The contents of the tank should be dumped upon arrival or a sanitation loop should be incorporated to disinfect the tank.
IF YOU ANSWER YES TO ANY OF THE ABOVE QUESTIONS THERE IS AN INCREASED RISK OF LEGIONELLA BEING PRESENT IN THE SYSTEM Should you decide that these risks are insignificant please review your risk assessment on a regular basis.
Legionella Risk
What should you do if you identify risks? • Introduce controls and system design to sanitise the cylinder. See schematics below using a DHW Priority to ensure water cannot stagnate anywhere in the system, eg remove redundant pipework, run taps/showers in unoccupied rooms; • Keeping water cisterns covered, insulated, clean and free of debris; • Insulate distribution pipework • Ensure thermostat on cylinder is set and locked at 65°C Example of a Heat Pump System with a DHW Priority Circuit
ASHP System
Time Clock DHW Indirect Cylinder
(Expansion Vessel, Tanks, Pumps Etc)
Buffer Tank Direct
Air Source Heat Pump (Wired for DHW Priority)
Radiator Heating
Example of a Heat Pump System with a DHW Priority Circuit & Solar System
Hot Water Out
ASHP System (Expansion Vessel, Tanks, Pumps Etc) 10cm Min
Radiator Heating
10cm Min
Anti-Legionella Loop Cold Feed
Buffer Tank Direct
Air Source Heat Pump (Wired for DHW Priority)
Legionella Risk
Examples Example of a Heating System incorporating a Wood Fired Stove and a Kombi Tank Thermal Store System Boiler Gas / Oil Fired
Pump DHW Loading Circuit
Underfloor Heating Circuit
Pump Heating Loading Circuit
Wood Burning Stove
Example of a typical Heating System with DHW Priority Circuit & Solar System Rear View of Manifold
Central Heating Boiler
Anti-Legionella Loop
10cm Min
10cm Min
Cold Feed
Informing the Homeowner/ Tenant • This information booklet must be completed and left with the householder. • It is important to instruct the homeowner about the importance of temperature control within the cylinder. • After long periods of non usage, i.e. holidays it is ideal to dump the volume of the tank and replenish with fresh water. Further reference material: - National Guidelines for the Control of Legionellosis in Ireland, 2009 - Microgeneration Installation Standard: MIS3001 – UK
B9278A
