54/Plumbing Engineer April 2019
the main distribution system to serve fixtures. Subloops maintain hot water recirculation by reconnecting to the main hot water loop with a balancing valve. Balancing Valves Don't forget the balancing valves! Since the intent of the hot water recirculation system is to maintain the tempera- ture throughout the distribution system, each branch needs to be balanced to achieve adequate flow for each subloop. Without balancing, water in a recirculation system would follow the path of least resistance. Subloops far from recir- culation pump would not be recirculated. When it comes to balancing valves, the more, the better. Do not shortchange the system; ensure each subloop has a balancing valve because without them it is difficult to experience the added benefits of the recirculation system. Balancing valves can either be pressure-dependent or self-actuating. Pressure-dependent valves - as the pressure changes, the flow will change as well - would be consid- ered the traditional method of balancing in domestic appli- cations. Self-actuating valves are pressure-independent. One of the up-and-coming technologies in balancing devices includes thermostatic balancing valves that auto- matically and continuously maintain a set water tempera- ture at the end of each domestic hot water supply. As the water cools at the end of a hot water loop, the calibrated valve adjusts to allow a greater flow through the valve until the water reaches the desired temperature. It solves the problem of delayed hot water delivery. The idea is that the valve only passes water needing to be reheated, whereas manual balancing valves allow water to pass through even if the temperature meets the desired temperature. Whether the system is composed of manual balancing valves or thermostatically self-adjusting balancing valves, all valves must be tested and commissioned to ensure that domestic hot water return flow rates are providing specified water temperatures circulated through each circuit. Hot water recirculation loops contribute to occupant safety and comfort, as well as energy and water conserva- tion. Through the process of recirculating unused hot water back to the heating source, constant water supply tempera- tures are provided to each fixture at minimized wait times. A properly balanced system with sufficiently designed dis- tribution provides significant water savings through timely water delivery, resulting in energy savings that lead to lower operating costs. Michelle Shadpour is a graduate from the University of Southern California with a bachelor's of science in Mechanical Engineering. As a Project Manager at SC Engineers since 2016, Shadpour has developed a diverse portfolio of highly complex plumbing projects. Her experience includes designing HVAC and plumbing systems for a variety of facility types including state- of-the-art laboratories; net-zero energy buildings; and hospitals. In addition to serving as a committee chair for ASHRAE's TC 1.4, Control Theory and Application, Shadpour is one of 2017's "New Face of Engineering" and was named one of 2018's Top 10 Engineers in Their 20s.
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