36/Plumbing Engineer March 2021 Plumbing Engineer March 2021/36
valve specification will be the magic bullet necessary to increasing building water temperatures while ensuring occupant safety. The American Society for Sanitary Engineering (ASSE) is the industry authority on developing perfor- mance standards, testing and certification of valves for the use of scald prevention. ASSE set seven standards for different valve types based on location and use in a plumbing system (https://bit.ly/39GnFk3). Many of the ASSE certifications should be common language in a plumbing engineer and building owner's repertoire. We will discuss the most commonly used standards, the applications for each standard and the tricks to success for each. One key factor to this article is the understanding of what is "scalding." ASSE defines scalding as: "Hot water exposure for a time period long enough to cause a ther- mal injury. Scald burn injuries can increase in severity at higher hot water temperatures or with longer exposures to a given hot water temperature." This is notably different than another phenomenon in plumbing systems known as "thermal shock," which ASSE defines as "a significant sudden change in tem- perature from hot to cold or cold to hot, or hot to hotter that causes a bather to violently react, which can lead to a slip and fall injury." It is important to understand the difference. ASSE developed performance criteria for both, but not all ASSE standards discussed protect against both scalding and thermal shock. Individual Shower and Combination Tub/Showers: The ASSE 1016 Valve ASSE 1016 automatic temperature-compensating and automatic pressure-compensating valves can come in three varieties: valves that adjust outlet temperature only, cold and hot water pressure, and some that do both. Automatic pressure-compensating valves, commonly known as pressure-balancing shower valves, compensate for fluctuating cold and hot water pressures at the inlet to maintain a constant outlet temperature. They protect against the thermal shock of hot water when a nearby toilet is flushed, which drops the cold water supply pres- sure to the shower valve. Pressure-balancing valves are less costly and work great under the assumption that the temperatures will not change with the valve's use. With that said, they are essentially "blind" to the incoming cold and hot water temperatures, so any change in water temp at constant pressure will affect the outlet temperature of the valve. Automatic temperature-compensating valves, com- monly known as thermostatic shower valves, adjust the mixing ratio of cold and hot water to provide a constant outlet temperature. They will compensate for changes in water temp at constant pressure; however, they will not protect against thermal shock due to varying system pressures. When distribution temperatures were lower for energy conservation measures, it was common to use a master mixing valve to determine the system operating tem- perature. At the showering fixture, pressure-balancing valves were common for thermal shock protection due to inevitable pressure fluctuations in a plumbing system. However, with rising distribution temps, pressure- balancing valves will likely be replaced by thermostatic valves that are not blind to the higher temps and offer better scald protection. Best practices for the use of these valves are: The showerhead flow rate must not be less than the manufacturer's published minimum flow rate for the valve (device). The temperature limit stop in a pressure-balancing valve must be set at the time of installation. It may need to be periodically adjusted for variations in water tem- peratures, such as seasonal cold water changes. In a typi- cal building with operations set at 120 F, shower valves could be set at 115 F. In response to the new CDC rule, if the building opera- tors modify the system distribution set-point to provide minimum circulation at 124 F, the shower valves will experience temps higher than the 115 F set-point and need to be reset. Distribution Systems: The ASSE 1017 Valve As mentioned previously, ASSE 1017 mixing valves have traditionally been used throughout plumbing dis- tribution systems at the hot water source to control system temperatures. Now that higher temperatures are being implemented across distribution systems, there is potentially less of a need for ASSE 1017 valves. Overall, plumbing engineers will need to specify valves at the point of use with higher distribution temperature require- ments. Flow Rate (gallons/minute) Allowable Temperature Fluctuation 0-5 gpm 3 F 5-40 gpm 5 F More than 40 gpm 7 F
Scalding
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