Very often, this system does not even show up on the maintenance schedules given to a service provider by the developer or building owner. Although it’s not unusual for plumbers to install circulation pumps to improve home hot-water circulation, this system is unique in that the pump runs only when hot water is needed. Despite their frustration, most homeowners shrug their shoulders at this problem, but not Gary Klein. On ½-inch lines, consider a lower velocity due to potential burrs or imperfections from potential faulty workmanship. On the other hand, the mismatch remains, and the potential for trouble exists should someone later decide to run the system at full capacity. The opinions expressed in this article are those of the authors and not the American Society of Plumbing Engineers. The extent of erosion caused by excessive velocity depends on the physical characteristics of the tube material or impediments to flow on the tube wall, such as the interior diameter (ID) of fittings or mineral deposits. The system can also assist in determining if water and energy conservation measures are being met. Ultimately, the recirculating system had to be repiped at a six-figure cost—and more, if you include lost revenues. PEX manufacturers recommend hot water recirculation velocity to be 2–3 fps. They collapse with enough force to erode microscopic pieces of metal if they are close to a fitting. “And, they want it now.” Klein is a strong advocate of The Metlund Hot Water D’MAND System, developed and marketed by Larry Acker, President of Advanced Conservation Technology, Inc. Metlund Systems. While this can also happen in non-metal fittings, the effects are much less dramatic due to the elasticity/plasticity of the materials and that ability to absorb some of the energetics of cavitation effects. hot water at the desired temperature to arrive at fixtures. Plastics Pipe Institute (PPI) test TN-53 recommends following the manufacturer’s recommend maximum velocities in situations outside of typical hot water usage, such as greater than 140° F (60° C) or non-typical applications like constant velocity. D. Sulfates are generally considered inert to copper. Normally, when not in use and flowing, the water in a hot water copper service line cools down to the ambient temperature of the household (70 to 80 °F). The valve is designed to close and keep the hot water in the pipes once it’s up to temperature. The issue rarely shows up clearly because many of the overbuilt systems are routinely operated at less than their full design capacity for a variety of reasons, such as low initial occupancies or low demand for hot water. But at high concentration, long-term exposure of sulfates might increase the pitting corrosion of copper. Copper is a soft and malleable material, and vulnerable to exposure to fast-moving hot water. In addition, all of the hot water lines, loops and branches included, are insulated. Furthermore, cloud-connected IoT applications can save energy by adding night setback sequences at low demand periods via throttling down the hot water recirculation flow to a minimum. the hot-water supply lines so that the pumps won’t op - erate when there’s already hot water in the pipes. However, its formation is also dependent upon the concentration of bicarbonates and pH. Investigation revealed the source: a pinhole leak in a copper pipe that was part of the 15-story building’srecirculating hot-water system. When annual or periodic service is not kept, failed PRVs can cause havoc by allowing high-pressure delivery into loops and suites. Design all hot water recirculating systems to keep velocities below 2 fps. The present author has also observed this type of hot water pitting in recirculating hot water systems (Nicholas, 2014), which shows that corrosion/erosion is not the only degradation mechanism that can occur in RHWS, although the latter is the most prevalent. The pump draws back the unused hot water back through the loop. At lower levels nitrate is considered to be not aggressive or it might decrease the pitting frequency. for hot water to appear at points of use while subsequently reducing wasted water going down the drain are recirculation systems, electric hot water temperature maintenance systems, and point of use heaters. In Kearney’s recirculating hot water systems, temperatures in the loop are continuously high. Install a circulating pump with a built in check valve in the line to prevent reverse flow. In fact, he helped refine the system so that now as little as one cup of water is wasted while waiting for the hot water to arrive. assures readers that “corrosion can be mitigated if systems are designed so that velocities do not exceed 4 to 5 fps (1.2 to 1.5 mps) in circulating systems”, • The Canadian Copper & Brass Development Assn. In general, cations (positive ions) do not participate in the corrosion reaction of copper, and hence, they have no influence on the corrosion reaction. Typically, a recirculating pump is used to pump hot water from a water heater through the copper hot-water pipeline, at the same time returning water that has cooled from the hot-water lines back to the water heater to be reheated. by Kevin Wong, MBA, BSc, CAE, and Avishai Moscovich MBA, P.Eng, LEED AP. In addition to reducing the flow, it is good practice to limit domestic hot water to an optimal temperature of 140° F (60° C), since increasing the temperature of potable water can substantially change its corrosive effects on materials. Traditionally, during building commissioning a circuit balancing valve is installed and set to allow design velocity in the recirculation line. Although less common, erosion corrosion could also occur in cold water lines. Unfortunately, these systems can be vulnerable to flow-accelerated corrosion, sometimes called erosion corrosion, which in turn can quickly mushroom into a costly and disruptive problem. By installing a connected flow meter and temperature and pressure sensors in lieu of the manual gauges, you can maintain the recirculation flow rate at optimal position and extend pipe life. It combines a 006e3™ ECM hot water circulator with Taco’s Hot-Link® Valve and Smart Plug Instant Hot Water Control® in one easily-installed package. 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