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Go With the Flow! (Part 1)

In today’s increasingly ‘green’ world it is enticing to jump on the sustainability bandwagon, especially when there is a personal benefit that complements the greater global initiative. Low-flow shower heads are one opportunity for the Owner that wants to be environmentally conscious, reduce energy consumption, and lower utility costs.

Low-flow shower heads can be found with listings from 1.0 to 2.0 gallons per minute (gpm). When compared to a conventional shower head, which typically flows at a rate of 2.5 gpm, the savings can be significant. In addition to reducing water consumption by 20 to 60%, the amount of energy needed to heat the water is also reduced. In a large facility, these reductions may provide further savings by allowing for smaller piping infrastructure and reduced water heater sizing.

“Water consumption over the next decade will be significantly impacted by low-flow technology.”

As with many innovative technologies, the change is not without pitfalls. The use of low-flow shower heads can lead to performance and safety issues, including temperature fluctuations and scalding, unless careful consideration is given to the characteristics of the shower valve. Current testing standards for shower valves limit the amount of temperature fluctuation allowed during operation. Unfortunately, these standards only require shower valves to be tested at a flow rate of 2.5 gpm. Testing at low-flow rates is not required. Each shower valve requires a minimum flow rate in order to properly operate and provide a consistent temperature. When the amount of water flowing through the valve is reduced, it may not be able to react to changes in temperature and pressure within the piping system. The result is temperature fluctuation, and in extreme cases, the valve may allow hot or cold water to pass without mixing. Limiting the temperature of hot water available at the shower to between 110 deg F and 120 deg F will reduce the risk of scalding should an operational problem occur.

The key to maintaining consistency is selecting a valve that the manufacturer has verified will operate properly with a low-flow shower head and then matching the valve to a head that meets the valve’s flow requirements. There are many shower heads on the market that claim to be low-flow, when in actuality they may only be low-flow over a small portion of their operating range. A single head can vary from 0.4 gpm to 2.8 gpm, depending on the inlet pressure, and still be marketed as low-flow. Since no two installations are identical, it is always best to ask the shower head manufacturer for a flow curve to ensure you are getting a consistent flow over a wide range of inlet pressures. Research is particularly important in renovation projects where the mixing valve style and minimum flow rate may not be known.

Water consumption over the next decade will be significantly impacted by low-flow technology. As sustainable products continue to evolve, many of the operational concerns will be addressed. In the interim, attention to the details can help assure that your experience will be a positive one.

Look for a continuation of this topic, and the impact of low-flow shower heads on shower compartment design, in the next newsletter.

– Timothy J. Scharf, PE, LEED AP

Tim is a Principal, a Licensed Mechanical Engineer, and a LEED Accredited Professional. Please feel free to contact Tim for further details regarding the above information.