56/Plumbing Engineer October 2021
120 F to 130 F in Building Hot Water Supply/Return As discussed in the first article in this series: "The rec- ommended temperature range (in 2021 UPC Appendix N) with the best Legionella control with low scald risk is the tempered hot range of 120 F to 130 F (49 C to 54 C). It is typically found in sinks and showers at good hotels." I just completed an audit of a children's hospital and found water in all patient restrooms and clinician sinks to be within this 120 F to 130 F range; showers were slightly below this range. Unfortunately, many believe the public faucet temperature limit of 110 F is related to scald risk. The public handwashing sink plumbing code requirement has nothing to do with scald risk; it is only intended as an energy-saving code. It is based on the requirements of ASHRAE Standard 90.1 dating back to 1989. Not maintaining a temperature range of 120 F to 130 F in both the hot water supply and throughout the return has, in fact, been the source of many outbreaks. Some believe that because studies show killing Legionella bacteria requires hours at 130 F, then the hot water supply and return need to be maintained above 130 F at all times for Legionella control. This is wrong and, in fact, counterproductive ! Maintaining hot water supply and return significantly above 130 F increases disinfectant destruction, corrosion rates and cor- rosion byproducts of zinc, iron and copper in solution; these metals further increase disinfectant destruction. Since Legionella doesn't grow above 116 F, then maintaining the hot water supply and return at 120 F or higher 24/7 will control it. In short: 1. Maintaining the hot water supply and return between 120 F to 130 F is good. 2. Maintaining the hot water supply and return significantly greater than 130 F is not good. As stated in the first article of this series, the Quincy Veterans Home implemented the VA Directive 1061 pro- tocols after its 2015 outbreak. This 1061 directive includes many statements that are not correct, including, "Water temperatures at [124 F] ([51.1 C]) or higher are necessary to inhibit Legionella growth in hot water systems," and "It is not possible to maintain water temperatures at the outlet that kill Legionella bacteria and simultaneously eliminate the possibility of scald injury in persons partially or fully insensitive to hot water temperature or having delayed or impaired response capabilities." Compare these statements with ASHRAE Guideline 12 2020, which correctly states that " Legionella growth slows, and they begin to die at water temperatures between 113 F and 120 F." And the 2021 Uniform Plumbing Code Appendix N states that 120 F to 130 F provides excellent Legionella control with a low scald risk. After implementing strategies that fully complied with VA Directive 1061, at a very high installation cost and continuing high maintenance cost, the Quincy Veterans Home had three additional outbreaks - one each in 2016, 2017 and 2018. What our team found during the investiga- tion was that the hot water supply temperature above 130 F destroyed all secondary disinfectant added to the system. Without any residual disinfectant, the thermal control pro- gram alone was not effective in preventing future outbreaks. Impact of Varying Temperature Schemes on Dead Legs, Drop Legs and Fixtures If the hot water return pump is constantly running, and the supply and return lines are consistently (i.e., 24 hours a day) maintained above 120 F, then Legionella will not grow in those circulating lines. Circulating the hot water supply and return between 120 F to 130 F does not protect the drop legs because even with excellent insulation, the temperature in those noncirculating lines quickly drops below 110 F. Even if the water is circulating at above 150 F, as was done at the Quincy Veterans Home, temperature alone is often ineffective in Legionella control in the drop legs. If the ambient temperature of the space surrounding the hot water drop legs is 70 F, and the temperature of the cir- culation loop is 120 F to 130 F, there will be a 50 F to 60 F gradient from the start of each drop leg at the loop to the end of the drop leg at each fixture (80 F at Quincy). At some dis- tance away from the circulating loop, the temperature will be 110 F. And at some further distance away from the circu- lating line and closer to the fixture, the temperature will be 85 F, right in the high-growth range for Legionella . This temperature gradient and the high Legionella growth range exists, whether or not the drop legs are insulated. Here is the dilemma: Uninsulated drop legs act like wicks sucking heat out of the loop, which increases energy costs; the quicker the drop legs cool down to below 50 F, the better for Legionella management. For energy reasons, ASHRAE 90.1 2020 has a provision requiring pipe insulation on at least the first 10 feet of each drop leg. The 2021 International Energy Conservation Code and the 2021 UPC include provisions requiring that the entire hot water distribution system be insulated from the water heater to the angle stops or valves near each fixture. Contrast this with the Dutch plumbing code, which pro- hibits insulation on hot water drop legs, knowing that the quicker the drop leg cools down below 85 F, the lower the Legionella risk. Pipe insulation on the drop legs will slow down but not prevent the temperature from dropping. This has the con- trary effect of maintaining the temperature on each drop leg in the high growth range for a longer period. Research into this pipe cool-down effect was published in 2005 by Dr. Carl Hiller, P.E., president of Applied Energy Technology ("Hot Water Distribution System Research - Phase 1"). The full report can be found at https://bit. ly/3yCWJuT. Drop legs are often 1/2-inch or 3/4-inch nominal pipe. While Hiller's research was conducted for another purpose, the results are relevant to this discussion. Figure 1 shows the
! # # "# # # # # # # # # # # # # # #
Legionella
Figure 1: Cool-down times for copper pipe. Graphics credit: Gary Klein
Previous Page