![]() ![]() ![]() Hot Water Return Pump Location It is not likely that the system will be able to use a quiet running 1,150 or 1,750 rpm motor. Systems that fail to predict and control flows in piping segments will likely short-circuit and take "the path of least resistance" Gauge-Reading Flow Control Devices and Check Valves Control of the flow quantity and direction at each riser through simple manually adjusted and set ball valves or square head cocks is another key to successful system arrangement. ![]() The NPSH available at the suction flange of the return pump can be calculated from the outlet pressure of the last remote pilot PRV location, adjusted by the static head formula for elevation, minus friction loss of flow in the piping segment to the suction flange.Īn overestimated discharge head selection for the hot water return pump without a control device in the pump discharge piping will allow the pump to "run wild" This includes all valves, fittings and the head loss of the remote pilot PRV used to blend the return pump discharge pressure back into the domestic cold water supply to the water heaters, but minus the net positive suction head (NPSH) available at the return pump suction flange location, from the accumulated returns above. ![]() The selection of the net discharge head of the hot water return pump can be figured as the total static head and friction losses of the pump discharge piping from the pump to the rooftop water heating equipment. Remember to include the accumulated flows in piping segments to the PRVs to properly size the remote pilot PRVs. = 0.433 psi) to estimate the inlet and outlet pressures at zone connection points that utilize remote pilot PRVs. It is necessary to use the static head calculation formula (2.31 ft./hd. Piping Friction Losses and Return Pump Head Using gauge-reading flow control devices to accurately set minimum flow rates from each riser and within each piping segment that joins the central return system allows accurate estimation of the friction losses in return piping, predictable piping circuit flows and direction, and selection of pipe sizes that are not erosive. Longevity of the water heating equipment is increased by the reduction of the operating pressure at the equipment, from near 150 psi for a basement location to approximately 25 psi for a roof location.īuildings that require multiple water pressure zones to limit useable water pressure at plumbing fixtures to the code-required maximums, and that also require circulated return systems from domestic hot water distribution risers, present a unique design challenge.Gas pipe is cheaper and smaller in diameter than flue pipe, returning square footage to the architectural floor plans and providing a construction cost savings.Therefore, a rooftop location for the equipment offers many long-term economic and design benefits. When natural gas is the preferred source of energy for domestic water heating in high-rise buildings, the static pressure of the proposed hot water distribution system will exceed the maximum relief valve pressure setting of 150 psi for the listed T&Ps required at the water heating equipment. ![]()
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