Types Of Water Pressure Booster Systems

Plumbing fixtures and equipment connected to a water source will function properly only when a minimum water supply pressure is consistently available. Whenever this minimum pressure cannot be maintained by the supply source, a means of boosting the water pressure should be considered.

The commonly used methods for boosting pressure are

1. Elevated gravity (tank) systems

2. Hydropneumatic tank systems

3. Variable-speed-drive centrifugal pump booster systems

4. Tankless constant-speed multiple centrifugal pump systems

5. Limited-storage, constant-speed multiple centrifugal pump systems

Table 1 identifies the significant advantages and disadvantages of each system.

Although gravity and hydropneumatic tank systems have some distinct advantages, most installations favor constant-speed multiple-pump and variable-speed-drive systems. Because gravity and hydropneumatic tank systems are now seldom specified, they will not be discussed in detail here. Multiple-pump systems are well suited for high-rise buildings, apartment buildings, schools, and commercial installations. Variable-speed-drive systems are particularly suited for industrial applications, where control precision is required and maintenance capability for complex electronic apparatus is present.

It is important to remember that the primary function of a pressure booster pump for a building, whether variable- or constant-speed, is to maintain the desired system pressure over the entire design flow range. It is also important to recognize that the cold water service piping configuration is an open-loop system, not a closed-loop system as it is in

TABLE 1 Comparison of significant factors for pressure booster systems

System type

Advantages

Disadvantages

Elevated gravity tank

Simplicity, large storage capacity, low energy usage, reserve storage capacity for fire protection

Hydropneumatic Location not critical, low energy tank

Variable-speed drive: Fluid couplings

Variable-speed drive: ac type

Tankless constant-speed multiple pump

Limited-storage constant-speed multiple pump usage, limited storage capacity, pump does not run when there is no demand, operation in optimum pump flow range Simple controls, off-the-shelf motor, standby provision less costly than for above units

Low motor current inrush, precise pressure control, higher than 3600 rpm possible, few mechanical devices, large power capability at lower first cost

Relatively low first cost, uses time-proven components, compact size, inherent partial standby capacity, extra standby capacity inexpensive, location not critical, good pressure regulation

Shuts down during very low water demand, uses time-proven components, standby capacity inexpensive, location not critical, limited water storage, no air-to-water contamination with diaphragm tank

Size and weight, water damage potential, freeze potential if roof-mounted, corrosion and contamination potential, limited pressure for floor immediately below tank, possible unsightly appearance, periodic cleaning and painting Requires compressed air source, corrosion and contamination potential, large pressure variation, relatively large, standby provision costly Slow response to sudden demand change, may require heat exchanger to cool drive, slip losses result in lower maximum speed and higher motor power, requires selective application, no water storage Complex electric circuitry, high initial cost for low-power units, may require special motors, motor low-speed limitation, rapidly changing technology, requires selective application Continuously running lead pump, difficult to accurately determine capacity split among pumps, no water storage, problems associated with low flow rates

No significant disadvantages, tanks with high maximum working pressure may be difficult to obtain heating and cooling systems. With an open-loop system, the static head above the pump is not canceled by the down leg of the piping, and therefore the pump must develop a head equal to or greater than the static head, even at zero flow (with suction pressure at design). Review Sections 8.1 and 8.2 for further discussions on closed-loop systems.

Variable-Speed-Drive Pressure Booster Systems Initial variable-speed drives were fluid couplings, magnetic couplings, and liquid rheostat (wound rotor motor) drives. The coupling-type drives were driven by a constant-speed motor, with the coupling output shaft varying in speed. With the advent of solid-state electronics technology and circuit miniaturization, most variable-speed drives currently used for pressure booster applications are of the solid-state, ac, adjustable-speed type. These drives are discussed in Subsection 6.2.2.

Variable-speed drives are usually specified for their low operating cost potential. To achieve the energy-savings goal, the system conditions should cause the drive speed to vary between 50 and 75% of full speed during most of the operating period.

The pump speed, head, and flow relationships are expressed by the affinity laws:

Flow varies directly as speed:

Head varies directly as the square of the speed:

Hi=a Nb2

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Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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