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Piping System Design

Use of Mixing Valve

Master thermostatic mixing valves are used to control an entire water distribution loop or major sections of a loop. A master thermostatic controller can be installed between tanks and taps to maintain a high temperature in tanks but lower temperatures at taps. This allows temperatures to be high enough to reduce the chance of Legionella bacteria breeding in your water heater and not risk scalding at the tap.

Ron George CPD, President, Plumb Tech LLC

With 35 years of experience designing plumbing and mechanical systems for several major architectural, engineering, and design & construct firms. He has designed plumbing, mechanical, and fire protection systems for all building types including airports, stadiums, industrial manufacturing facilities, office buildings, commercial and retail buildings, hospitals, laboratories, prisons, jails, hotels, apartment buildings, military projects, high rise and educational facilities.

The typical hot-water tank keeps approximately 65% of the tank at the set temperature; the other 35% will be cooler. Some water heaters develop a warm zone at the bottom of the tank (beneath the heating element) where scale and sediment often accumulate, providing a perfect habitat for Legionella.

Because hot water use is constant, temperatures may not vary much in hospital hot-water tanks. If temperatures do vary, consider relocating the supply and return taps, installing a top-to-bottom circulating pump or insulating the underside of the vessel.

Installing thermometers at various locations of the tank (say one at each and a third at the middle) will make regular temperature checking easier.

  • Extend recirculation lines to the point farthest from the supply.

  • Run all lines at a slight fall to make draining the system easier and to reduce air locks.

  • Run hot piping above cold piping to prevent warming of cold water.

  • Ream all pipe ends to remove burrs. Burrs can trap sediments and cause corrosion.

  • Apply pipe compound only to male threads to keep it from being pushed into the fitting when the join is made.

  • Minimize Cool Zones in Hot Water Tanks

  • Use copper-pipe