Circulation Pump Selection

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StainlessSteel and Bronze circulators are typical for open loop hydronic/radiant heating and domestic hot water recirculation applications. Threaded and sweat connection types are particularly common for the later application type, making it easier to connect the circulator in line with an existing water line.

Although radiant heat manifold and PEX tubing sizing are a different topic, let's assume, for example, that a manifold has 8 outlets with 1/2" PEX tubing installed at 300ft length per loop and the system calls for 72,000 BTU's.

It is important to understand that other components installed within a given zone (such as the radiant heat manifold itself, fittings, check valves, mixing valves, balancing valves, heat exchangers, PEX tubing length (different diameters), etc.) also have to be considered when sizing a circulator pump (see Scheme 1 below). Pressure drop information is usually available in a form of technical specifications or submittal sheet supplied by the manufacturer.

NOTE: Pump head is a term used to describe the force the circulator develops to overcome pressure drop (pipe, fittings and valves). In a Closed System, "pump head" is NOT the height of the building. Height (#10 on the Scheme above) is not taken into consideration.

However, Taco 009 circulator is designed for high head and low flow applications only, meaning that is the flow requirements were to slightly increase, the circulator's performance would fall dramatically.

Similarly is true for the Taco 0010 model. It is designed for use in high flow and low head applications only, so if the pressure drop in the system was to change due to additions or modifications, the pump's performance would drastically decrease.

Pump selection and configuration is streamlined with the Pentair Encompass Pump Selection tool. Designed for commercial building engineers and distribution partners, Encompass provides an easy selection of a pump based on the requirements of service. Featuring a search-by-application feature, you can select the pump and size that best fit your installation needs. Additional enhancements to the tool have been introduced for greater functionality.

From our residential and commercial water solutions, to industrial water management and everything in between, Pentair is focused on smart, sustainable water solutions that help our planet and people thrive.

Pumps are selected based on their characteristic curve, which shows the relationship between the pump head and the flow rate of water. The operating point of the system is plotted on the pump characteristic curve, which is the intersection of the design flow rate and head. The operating point should be on or slightly above the pump characteristic curve and as close as possible to the point on the curve with the highest efficiency. If several pumps meet the specified characteristics, preference should be given to the pump with lower power. If the flow rate will be changing over a wide range, a pump with a flatter characteristic curve should be selected.

When selecting a circulation pump for a heating or hot water supply system, it is important to consider the possibility of hydraulic imbalances, which can result in poor water circulation in remote circulation loops. By choosing a pump with a margin for flow rate and head, it is possible to compensate for minor hydraulic imbalances. For heating systems, it is recommended to choose a pump with a 10-20% margin for head and a 20-30% margin for flow rate. However, it should be noted that if the flow rate increases by 1.3 times, the pressure drop in the system will increase by 1.7 times.

For heating systems with thermostatic radiator valves, a slight deficit in pump flow rate is acceptable due to the 10% increase in the surface area of heating devices and the non-linearity of the decrease in heat transfer of heating devices with changes in flow rate.

The noise characteristics of the pump are often the deciding factor when choosing circulation pumps for engineering systems in residential buildings. For pumps installed in spaces where people constantly reside or in adjacent spaces, pumps with wet rotors are recommended because they operate the most quietly.

The water flow circulating in the hot water supply system is proportional to the thermal losses in the pipelines of the hot water supply system and inversely proportional to the temperature difference between the water entering and returning from the hot water supply system.

The head losses in the heating and hot water supply systems are determined by hydraulic calculation and must be indicated in the projects for the installation of these systems (usually ranging from 2 to 7 m).

When determining the pump head, the natural circulation pressure of the system should not be ignored, which arises due to the difference in the density of hot water entering the system and cold water leaving it. The magnitude of the natural pressure is positive if the water heating center is lower than the cooling center and negative if the heating center is higher than the cooling center.

During different periods of the heating season, the magnitude of the natural pressure varies and accordingly has a different effect. The influence of the natural pressure can be eliminated by installing automatic pressure drop regulators or flow regulators. The larger the proportion of natural pressure in the circulation head, the greater its effect.

Cavitation in a pump occurs when the water pressure drops to the saturation pressure. Cavitation is essentially the rapid formation and collapse of vapor bubbles, which results in hydraulic shocks on the pump impeller. Cavitation in a pump is accompanied not only by increased noise but also accelerates the process of its wear and tear.

To avoid cavitation in a pump, it is necessary to ensure that the pressure in the inlet pipe exceeds the saturation pressure. It should be noted that the saturation pressure depends on the temperature of the water, with lower temperatures resulting in lower saturation pressure.

Some manufacturers indicate the cavitation characteristic of the pump - NPHS - which is numerically equal to the minimum absolute pressure in the inlet pipe of the pump, at which cavitation-free operation is guaranteed.

A spa circulation pump is often an additional component in hot tubs that works with the Ozonator, ensuring a continuous flow of water through the filtration system to maintain cleanliness and prevent bacterial or algae growth. Various spas also require a circulation pump as the primary pump that heats the spa water.

Many hot tubs use a jet pump to move water through the filters and heat the spa. However, when the hot tub is not in use, the stagnant water provides the perfect environment for bacteria growth. A hot tub circulation pump as part of an ozone system addresses this by keeping the water moving 24/7, even when it is not being used.

Several spa manufacturers utilize a circulation pump as the primary pump that circulates water through the heater, making a circulation pump an essential component for spa operation. If your spa heats with a circulation pump, you will need to replace the faulty part as soon as it fails in order for the spa to continue to operate correctly.

Ultimately, a circulation pump has many advantages. For example, its smaller size and low power result in energy savings, while the consistent circulation ensures water quality and an even water temperature throughout the hot tub. A hot tub circulation pump also helps distribute water chemicals, ensuring uniform and effective treatment.

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Selecting the right hot water circulator pump for a house is a critical process that involves understanding the specific heating requirements of the property. This selection is influenced by several key factors such as the heating load, flow rate, house size, and the type of heating system. A systematic approach can ensure the chosen pump is efficient, effective, and suitable for the specific needs of the residence.

Next, estimate the flow rate needed for the system, expressed in cubic meters per hour (m/h). This calculation is vital for selecting a pump that can circulate the necessary volume of water. The formula

For a house of 200 square meters with these specific characteristics, a circulator pump that can deliver about 5.73 m/h and has a head pressure of 3 to 4.5 meters would be most suitable. This selection ensures that hot water is efficiently circulated, providing consistent and effective heating across both floors.

Circulator series pumps are those small inline pumps that have fixed impeller choices with no impeller trimming available. When these pumps have ECM technology, the speed selections are also available in steps. What happens if the selection you want is just over the curve and the next selection is much larger? This is a perfect example of the difference between the engineer and the scientist.

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