Circulators

A circulator is a critical part of any domestic hot water system. Essentially a small pump, among its jobs are moving hot water around a hydronic system, such as radiant flooring; providing instant hot water to sinks and showers; enabling a home to be zoned; and sending liquid to a heat exchanger in a solar or geothermal system.

Circulators are sometime confused with feed or pressure-reducing valves. It’s the job of a feed valve to pressurize the water in a hot water system and lift it to the top floor. The circulator simply makes water flow around pipes already under pressure.

If the system is completely filled with water and in perfect balance, the only forces a circulator must overcome are friction caused by pipes and fittings, inertia of the water, and turbulence. Think of a small child pushing a roundabout—she doesn’t have to push against its weight, just the low friction of the bearings. Thus, a circulator needn’t be very large to do its job, nor much of a power drain.

The forces a circulator works against introduce two pump terms—pressure drop and pump head. Pressure drop is the friction created by water rubbing against pipes and fittings. Pump head is the force a pump needs to overcome pressure drop and make water flow. Pump head refers not to the height of a building but to pipe length and number of fittings—a long, low buildings can have a high pump head, in other words.

How does a circulator create the force it needs? A type of centrifugal pump, centrifugal force created by the impeller’s spinning vanes pushes water to the outer rim—think of children spinning quickly on that roundabout—where it is then fed into a smooth (or “volute”) channel. Because this exit channel is smaller than the entrance, water is forced out with power enough to overcome pressure drop. More water then moves into the pump’s entry channel to fill the void.

The correct placement of a circulator is important. A circulator should be placed away from the compression tank. Doing this increases overall system pressure, making air removal easier and eliminating noise. Place the circulator before the tank and pressure will drop whenever the circulator starts, releasing dissolved air and causing noise and air-binding problems.

Xylem RCW manufactures many kinds of circulator, and your dealer, distributor, or installer can help you choose the right solution for your needs. There are oil-lubricated circulators; wet rotor circulators lubricated by water, which are often called maintenance-free because they don’t have to be oiled; and newer highly efficient Electronically Commutated Motor (ECM) circulators. For potable water supply, you will want to use lead-free circulators.

ECM circulators are the most energy efficient choice. They feature spherical magnetic motors that are managed electronically to provide smooth, variable speed operation; they operate on as little as 10 watts of power; and they are up to 68% more efficient than standard circulators. They are also shaftless and have ceramic bearings, making them truly maintenance-free and corrosion- and scale-resistant.