Minimizing Legionella Bacteria in Building Water Systems

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Kemper has Developed an Innovative Solution for Minimizing Legionella Bacteria in Building Water Systems

By: Ron George, CPD, President, Plumb-Tech Design & Consulting Services LLC,

There is a relatively new product on the market that is being sold by Kemper Industries.  It allows a plumbing system design that flows or circulates cold and hot water right to each fixture in order to eliminate stagnant water in dead legs.  Dead legs are where bacteria and viruses tend to grow when the chlorine or other water treatment chemicals in the water dissipate over time.  As the water treatment chemicals dissipate, the bacteria and other microorganisms in the biofilm will grow when the conditions are right for growth.  The Kemper Hygiene System will also eliminate the national pastime of waiting for hot water or fresh water to arrive at a tap. Kemper also has a faucet that circulates the water right up to the tip of the faucet.  The hot water in these systems will be there before your hand can make it from the faucet control to the flow of water coming from the spout.

Kemper Hygiene systems makes all of the components for a complete system including their patented flow splitter fittings that allows flow through the branch piping, isolation valves, flow control valves, water sampling valves, temperature sensors, flow sensors, flow meters, control panels with data storing for conformance to water management plans and motorized control valves with an air gap fitting for periodic flushing of the system if the sensors note that the last branch has not been used in the predetermined period of time or if it has not flowed the required flow to adequately flush the system.   These systems are designed to direct a portion of the water to flow through every branch and right up to every fixture on the way to the end fixture. This system is ideally suited for minimizing Legionella in building water systems without adding water treatment chemicals.  If the municipal water system cannot provide the required water treatment chemical levels, then supplementary water treatment chemicals can be used in concert with this system to distribute the water treatment chemicals to every part of the piping system.  This cannot be done with a conventional trunk and branch plumbing system design without spending the time to flow water from every fixture for a period of time sufficient to bring the water treatment chemicals up in that branch.  This system can allow flushing and disinfection without wasting large volumes of water flushing at each fixture. This system design allows flows through all the branch piping to and through the tee where the fixture supply connectors are connected to the angle stops. Some designs allow circulated or parallel flow right up through the faucet.

This has been very popular in Europe because they have legislation requiring all commercial buildings to flush water from every fixture for a specified period of time and to document this flushing every three days to prevent stagnation. Most water supplies in the USA are treated with some form of chlorine, mono-chlorine or chlorine dioxide. over time these water treatment chemicals dissipate and are ineffective at fighting Legionella bacteria which causes Legionnaires Disease. This dissipation accelerates when the water has more contaminants, when the pipe systems are old and full of scale and iron oxide, and when the water temperatures are elevated.  If the water treatment chemicals dissipate under the aforementioned conditions, the microorganism can begin to grow and flourish. if this occurs in a seldom used pipe branch, the microorganisms can grow to very high levels. The cold water (CW) and hot water (HW) systems are separate designs.  CW systems utilize a flow sensor or temperature sensor on the farthest branch to monitor for usage utilizing a control panel.  When the end branch has not been used or flowed with a sufficient flow volume to flush all the upstream pipe branches, during a specified time frame, the controller will then open a motorized control valve which will flush cold water through the system to bring in fresh water with sufficient water treatment chemical levels.  We must remember that health and safety is more important than water or energy conservation.  We are to the point of diminishing returns with respect to lowering water flows to fixtures. We should study the cause and effect of water conservation measures. There should be a committee study each proposal for water flow reductions prior to mandating them into law.  We have had water flow reductions recently mandated that are seriously affecting the ability of the plumbing system to provide a safe and healthy plumbing system.  We must have enough flow in the pipes to maintain water treatment chemical levels and we must have enough flow in the drains to carry away the waste with sewer backups.  When the CW branch lines on this system are flushed there are controls to minimize the flush to make it only long enough to maintain the water treatment chemical levels. The flush is typically long enough to bring the chlorine levels up to above 1 ppm or it can sense volume or temperature change indicating fresh chlorinated water.

The HW system is designed different from the cold water system.  The HW system is designed in accordance with industry Guidelines (ASHRAE Guideline 12) which calls for a minimum of 124 F at the coolest spot in the hot water return (HWR) circulation system. (at the point where the HWR connects to the CW inlet to the Water heater) If that point is above 124 F the entire HW system will be above 124 F. Tests show Legionella bacteria has a growth temperature range from 68F-122F and the Ideal Growth Range is around 95F-115F.  ASHRAE has suggested keeping HW temperatures a couple of degrees above 122 F (124 F min. in Guideline 12).

So keeping the HW above 122 F will prevent any legionella bacteria from multiplying to higher levels while in the building water system.
This recommendation for 124 F minimum hot water temperature combined with the heat loss in a typical HW circulation pump calculation for a 20 degree temperature difference (for systems with mixing valves that require a 20 degree temperature difference) must have a hot water delivery temperature of about 144 F.  This can be done by utilizing a mater thermostatic mixing valve that is adjusted to maintain the hot water return temperature above 124 F.  If a manufacturer that has a 10 degree F or 5 degree F mixing valve is used, then a larger flow and lower temperature difference can be utilized.  I would caution you to check the hot water velocity in your circulated lines.  The copper development association recommends a maximum velocity of 2-3 feet per second (FPS) in copper pipes above 140 degrees F,  and a maximum velocity of 5 feet per second in hot water pipes up to 140 F and a maximum velocity of 8 feet per second in cold water pipes. The velocity recommendation is to prevent excessive noise, water hammer and erosion of the inner wall of the pipe, which can lead to pinhole leaks.

Effect of Water temperature on Legionella
Below 68 F Legionella is dormant and will survive, but not multiply
At temperatures at or above 77 F Legionella becomes more active
At temperatures of 95 F to about 115 F Legionella bacteria will grow and multiply rapidly (Ideal Growth range)
At 122 F and up to 131 Legionella will survive, but not multiply
At 131 F Legionella begins to die (it takes about 5-6 hours)
At 140 Legionella dies in 32 minutes
At 151 and above Legionella dies instantly

158 F is considered the disinfection temperature for thermal disinfection, This allows an elevated temperature to penetrate layers of biofilm and scale inside pipes.  However many hot water systems are not capable of providing hot water in sufficient volumes for a period of time long enough to provide a proper heat and flush disinfection.  Instantaneous systems are often designed to only raise the temperature to the usage temperature at peak flows.  Storage type heaters are designed to store HW at elevated temperatures in a batch that can handle the peak hourly demand, but typically are not designed for the continuous flow and BTUH input required to heat and flush a large system for more than the peak period of time.

It is for the above reasons that the ASHRAE Guideline 12 recommends storing Hot water at or above 140 F which will provide for pasteurization of the hot water over a short period of time and it will keep the distribution and return piping above 124F which will keep the hot water above the Legionella growth temperature range. When doing this it is very important to make sure the maximum temperature limit stops on the shower valves and lavatory faucets are set. If older style 2-handle shower valves are still present, I think it is time to start replacing them with code compliant anti-scald valves that can be adjusted to limit the hot water outlet temperature to a safe temperature below 120 F. For lavatories and other fixtures requiring lower temperatures, a limit stop can be specified on single handle lavatories, or the hot water can be circulated up to the faucet as shown in the attached video, or point-of-use thermostatic mixing valves conforming to ASSE 1070 should be used to prevent scalding. The maximum temperature allowed in most codes to prevent scalding is a maximum of 120 F, but the adjustment allows an adjustment to a lower temperature which would be safer depending on the situation or location. Other options are available like an ASSE 1062 device (Temperature Actuated Flow Reduction (TAFR) device, which can be installed on shower heads, bathtub fillers or sink outlets to shut off the flow of water if the temperature exceeds 120 F.


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