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ASHRAE (American Society of Heating Refrigeration and Air Conditioning Engineers) and the National Sanitation Foundation International (NSF International) have announced they will soon finalize a standard for the prevention of injury and disease associated with building water systems. 

It will be called ASHRAE/NSF Standard 514 and will replace the NSF 444 standard, which has been in development, but has not been completed. In 2015 ASHRAE published Standard 188, Legionellosis: Risk Management of Building Water Systems and will soon publish a supplement called ASHRAE Guideline 12. The new 514 standard will reference these, and be broader, covering waterborne pathogens beyond Legionella. 

It is being designed in accordance with ANSI requirements. When it is complete, the ANSI designation will likely be added after ANSI reviews the text.

The urgency for 514 has increased as regulators, public health departments, building owners and health-care facilities need help managing the risk of waterborne pathogens and other hazards.

The following two paragraphs provide tips on how to ensure systems are not likely to promote dangerous Legionella bacteria. They were published recently in Plumbing Engineer magazine, and prepared by Ron George, who has been active on the committees for all of the standards mentioned above.

Piping system design to minimize bacteria growth; Extend recirculation lines to the point farthest from the supply and maintain temperatures above 124 F at the point where the hot water return gets back to the water heater; Run all lines at a slight fall to drains at low points to make draining the system easier and make piping take-offs and connections to reduce airlocks and trapped sections of piping; Run hot piping above cold piping to prevent warming of cold water; Run hot piping as far away from cold water piping as possible to minimize heat transfer to cold water piping; and Ream all pipe ends to remove burrs. Burrs can trap sediments and allow a food source for Legionella. Burrs also can create local turbulence, which can cause erosion.

In addition: Minimize cool zones in hot water storage tanks by recirculating the hot water system and storing hot water at or above 140 F; A good system design would maintain a temperature above about 124 F at all parts of the system; Install thermometers: at the inlet and outlet of all water heaters; in the hot water return piping just ahead of the hot water return circulating pump, which should be located near the water heater; and at the inlets and outlet of all mixing valves; and Digital temperature actuated mixing valves should be used to control the entire hot water supply and return distribution loop or major sections of the circulated distribution system. Balancing valves should be used for branches. This allows temperatures to be high enough in the water heater to pasteurize the water and prevent Legionella bacteria from growing in the hot water tank. Point-of-use mixing valves or temperature-limiting devices should be used to limit the water temperatures at fixtures and prevent scalding.