Circulator pump Use with domestic hot water

A circulator or circulation pump is a special type of pump used to circulate gases, liquids or slurries in a closed circuit.They are commonly found in circulating water in hydronic heating or cooling systems.Because they only circulate the fluid in a closed loop, they only need to overcome the friction of the piping system (instead of lifting the fluid from a lower potential energy point to a higher potential energy point).The circulation pump used in the circulation system is usually an electric centrifugal pump.In domestic use they are usually small, sealed and rated at fractions of a horsepower, but in commercial applications they range in size up to many horsepower and the motor is usually coupled to the pump by some form of mechanical coupling Body separation.Seals used in domestic applications typically combine and seal the motor rotor, pump impeller and support bearings in a water circuit.This avoids one of the main challenges of larger two-part pumps: maintaining a watertight seal where the pump drive shaft enters the pump body.

Small to medium circulator pumps are usually fully supported by the pipe flanges that connect them to the rest of the circulation piping. Larger pumps are usually pad mounted.Pumps intended only for closed loop systems can be made with cast iron components, since the water in the loop will be deoxygenated or treated with chemicals to inhibit corrosion.However, the pumps through which the oxygenated drinking water flows must be made of more expensive materials such as bronze.

Use with domestic hot water 

Circulator pumps are often used to circulate domestic hot water, so taps provide hot water immediately on demand, or (more energy efficient) for a short time after a user needs hot water.In areas where water conservation has become increasingly important as populations expand and urbanize rapidly, local water departments offer rebates to homeowners and builders who install circulating pumps to save water.In a typical one-way plumbing without a circulation pump, water is simply sent through the pipes from the water heater to the faucet.Once the tap is turned off, the water remaining in the pipes cools down, creating the familiar waiting hot water the next time the tap is turned on.By installing a circulation pump, a small amount of hot water is continuously circulated through the pipeline from the heater to the farthest fixture and back to the heater.The water in the pipeline is always hot, and no water is wasted during the waiting process.The trade-off is the energy wasted running the pump and the extra need for a water heater to make up for heat lost from the constantly heating pipes.While most of these pumps are installed closest to the water heater and do not have adjustable temperature capabilities, significant reductions in energy consumption can be achieved by using a temperature adjustable thermostatically controlled circulation pump installed on the last fixture of the loop.A thermostatically controlled circulation pump allows homeowners to choose the desired hot water temperature in the hot water mains, since most homes do not require 120°F (49°C) water from the tap immediately.Thermostatically controlled circulator pump cycles on and off to maintain a user-selected temperature and uses less energy than a continuously running pump.By installing a thermostatically controlled pump after the furthest fixture on the loop, the circulation pump can keep hot water ready until the last fixture on the loop instead of wasting energy heating the pipe from the last fixture to the water heater.Installing a circulation pump on the furthest fixture on a hot water circulation circuit is often not feasible due to limited space available, aesthetics, noise restrictions or insufficient power supply available.Recent advances in hot water circulation technology allow to benefit from temperature controlled pumps without having to install a pump as the last fixture of the hot water circuit.These advanced hot water circulation systems utilize a water contact temperature probe strategically installed at the last fixture of the loop to minimize energy wasted heating lengthy return pipes.Insulation applied to piping helps mitigate this secondary loss and minimizes the amount of water that must be pumped to keep hot water continuously available.Traditional hot water recirculation systems use the existing cold water line as the return line back to the hot water tank from the point of use furthest from the hot water tank.The first of the two system types has a pump mounted on the water heater, while a "normally open" thermostatic control valve is mounted on the fixture furthest from the water heater and closes once hot water hits the valve to control the flow of hot water and Cross-flow cold wire between water heaters.The second type of system uses a thermostatically controlled pump mounted on the fixture furthest from the water heater.These thermostatically controlled pumps usually have a built-in "normally closed" check valve that prevents water from the cold water line from entering the hot water line.Using a cold water pipe for the return has the disadvantage of heating the cold water pipe (and the water it contains) compared to a dedicated return pipe. Accurate temperature monitoring and active flow control minimize chilled water loss in the chilled water line.

Technological advances within the industry have allowed the incorporation of timers to limit operation to specific times of day, reducing energy waste by only operating when occupants are likely to use hot water.Other technological advances include pumps that cycle on and off to maintain hot water temperature, rather than continuously running pumps that consume more electricity.Energy waste and discomfort can be reduced by preventing hot water line siphonage in open loop hot water circulation systems that utilize cold water lines to return water to the water heater.Hot water line siphoning occurs when water in the hot water line is siphoned or forced into the cold water line due to the difference in water pressure between the hot and cold water lines.Use of a "normally closed" solenoid valve prevents non-hot water from being siphoned out of the hot water line during cold water use, significantly reducing energy consumption.Use cold water to instantly reduce the water pressure in the cold water line, and the higher water pressure in the hot water line forces the water through the "normally open" thermostatic crossover valve and the return check valve (only prevents cold water from flowing into the hot water line), increasing the pressure on the Water Heater Energy Requirements.