Plumbing Engineer October 2021/65
Consistency, Cost Savings Master mixing valves also keep domestic hot water temperatures con- sistent, even with large inlet temper- ature changes. As part of the ASSE 1017 certifica- tion, all master mixers must control the out- let temperature within a speci- fied range from the initial set point when there is a 25-degree increase to the hot water inlet tem- perature. The allow- able variance can range from 3 degrees to 7 degrees, depending on the size and flow rate. The majority of ther- mostatic master mixers hold to within 3 degrees, and digital master mix- ing valves are known to hold within 2 degrees. Without a master mixing valve, a large increase in hot water tem- perature can be a dangerous situation. Pressure-balanced shower valves are of particular con- cern since they do not offer thermal protection; large increases to the domestic hot water temperature will be directly felt by the end-user. If a master mixing valve is installed, the large increase in hot water temperature from the heat source is tempered down and end-users are better protected. Energy and cost savings are other benefits of install- ing a master mixing valve. Instead of having to provide 100 percent of the hot water needed for the building, the heater is only needed for a fraction of that when a master mixer is present in the system. Consider a system requir- ing a domestic hot water temperature of 125 F. If the hot water supply is set to 140 F with a mixing valve installed downstream, 83 percent of the volume needs to be heated, assuming the cold water temperature is 50 F. At 160 F, only 68 percent of the water needs to be heated. This reduction will save the facility energy, and the system becomes environmentally friendly. In addition, since the heaters are heating a lower volume of water, a smaller unit may be sufficient; wear and tear to the heater and related equipment are reduced. Installing a master mixing valve on a domestic hot water system is simply good practice. It adds an extra layer of safety to any system. Having a master mixer allows facilities to heat and store water at elevated tem- peratures, which kills Legionella bacteria while delivering safe hot water temperatures for multiple applications. If a heating system malfunctions and a large increase in the hot water temperature is seen, a master mixing valve will flatten the spike to the domestic hot water system. The inclusion of a mixing valve also will save energy and lengthen heater equipment service life. O Rick Cota is vice president of technical services at Leonard Valve Co.; Eric Costa is a mechanical engineer at Leonard Valve Co. For more information, visit www. leonardvalve.com.
Figure 1: Legionella Growth in Water with Relation to Temperature Figure 2: Burn Times at Different Hot Water Temperatures Leonard Valve's NV-150- LF Nucleus digital master mixer valve
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