Hot waterrecirculationsystemdesign

The pressure reducing pilot commands the valve to throttle/close when the downstream pressure increases ABOVE the pilot pressure set point and to open the valve when the downstream pressure decreases to BELOW the pilot pressure set point.

The hydraulic pressure reducing valves are equipped with a pressure reducing pilot designed to hydraulically sense the downstream pressure.

Recirculatingpump for tanklesswaterheater

In Irrigation PRVs are required in water headers in the entry of lower elevation fields, pivot-machines, low pressure systems like dripping pipes and more.

How it Works. In a conventional system with a central water heater, any cold water standing in the pipes between the heater and the point-of-use is dumped down the drain as hot water travels from the heater.

Recirculating hot water systemdiagram

Some have throttling devices to cope with low flows, and others have different mechanisms to eliminate/reduce cavitation.

*This example refers to 3-way control method. In Waterworks and Buildings 2-Way is common as well, which has somewhat different principles of operation.

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Hot water recirculating systemwith dedicated return line

System pressure can vary due to many different reasons. Pumps starting, changes in topography, pipe characteristics, the resistance of equipment along the system, leaks & water theft and of course the demand flow pattern which has a direct effect on the pressure loss across the pipeline.

Hot water recirculatingpump installation diagram

Based on this understanding there are many different types of Pressure Reducing Valves and configurations to optimally suit these varying requirements

While in Irrigation & Fire Protection, flow is constant and occurs in shifts/pulses, depending on the crops or firefighting emergency events.

Hydraulically operated pressure reducing control valves reduce a higher upstream pressure to a constant lower downstream pressure, regardless of fluctuating demand or varying upstream pressure.

Hot water recirculatingpump without return line

In a demand recirculating system, when the system is activated the pump starts recirculating cooled water that's been sitting in the hot water line and sends it back to the water heater through the cold water line. When the water reaches a desired temperature a control turns off the pump. This process is similar to turning on the hot water faucet and letting the water run until it gets hot, but instead of the water going down the drain, it is simply returned back to the water heater—saving energy and water.

When downstream pressure is lower than the required set-point, the pilot drains water from the control chamber to the atmosphere and the valve opens.

hot water recirculating systemwith built-in timer

How does ahot water recirculatingpump work

In high rise buildings, PRVs are located on every floor or every few floors, for protecting the department’s plumbing and low rated fittings & connections from overpressure.

Demand hot water recirculating systems can save water and energy in some situations. Potential benefits of installing a demand recirculating system during your next new construction or home retrofitting project, include:

In municipal networks pressure reducing valves (PRV) are required at the inlet of pressure zones or DMAs (District Metering Areas). On the one hand, for protecting the equipment at the downstream and  household plumbing  from overpressure. On the other hand, guaranteeing sufficient & reliable pressure for the consumers.

Some rely on a 3-way control loop and others on 2-way. Some are full bore for minimal head loss during insufficient inlet pressure and others are reduced bore for achieving efficient pressure regulation.

In an integrated loop system, hot water is re-circulated intermittently. Hot water is returned to the water heater through the cold water pipes. This process raises the temperature of the cold water slightly, but it returns to the usual cold temperature in a short time.

When downstream pressure is higher than the required set-point, the pilot allows water to flow from the upstream to the control chamber and the valve tends to close.

When downstream pressure is equal to the required set-point, the pilot keeps the water in the control chamber and the valve remains in the same position, not opening or closing, and thus retaining the set pressure.