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Old tricks for new dogs: offering engineers a simple alternate system to use when performing domestic hot water temperature maintenance in high-rise buildings.

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Hot water recirculation for high-rise buildings has been problematic since high-rise construction began, and it has become more complicated as buildings get taller. The basic systems referred to in the codes, text books and standards work well for shorter buildings but do not address the special requirements of very tall buildings with multiple pressure zones. The hot water return pumps required to overcome the high pressures in these systems bring with them noise and vibration that, if not dealt with properly, will result m complaints from the building's inhabitants.

As each zone of the building is brought back to the water heater, they arrive at different pressures, and if this difference is too great, one or more zones may refuse to circulate. The pressure-blending valves required to manage these pressure variations require thoughtful and delicate adjustments. This is often beyond the performance capabilities of the installing contractor and must be done by a specialized balancing contractor. Additional problems arise if, after balancing, the operator changes the set point of the pressure-reducing stations or the pressure booster output.

In the past, some engineers have used a water heater in each zone with its own circulating system. This type of decentralized system has fallen from favor due to the space requirements for the equipment, flues, etc., required to support them. They did, however, provide an answer to the difficulties of multi-zoned recirculation systems by neatly sidestepping altogether the issues of combining competing pressures.

In this article, I will describe a system that does the same neat sidestep, as it...

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