Pump Pros Know- Pumping Systems in Commercial Building Services

Commercial buildings use pumps for a wide variety of functions, including heating, cooling, water pressure boosting, fire safety systems, wastewater systems, and often for swimming pools and fountains. These pump-based systems are vital for the function and consumption of more than 35% of a commercial building’s energy, so it’s important to understand the role of these pumps in these varied applications.

Open and Closed Systems

Applications can be categorized based on whether piping is open to atmospheric pressure. Cooling tower and hot water supply applications are common examples of open systems because the fluid is exposed to the atmosphere. Hydronic systems for heating or cooling are not open to environment—where the liquid is circulated—are examples of closed systems. This is an important consideration in pump selection because of the available atmospheric pressure or lack thereof, so material selection may be different for liquids exposed to atmosphere.

Drivers for Pumps

Pump drivers provide the power to the input shaft of the pump so it may operate and can be an electric motor or engine. The most common pump driver in a commercial building is an induction motor. Due to efficiency and control benefits, in smaller sizes there is growing use of electronically commutated motors, which are more efficient designs that have integrated variable frequency drives required for operation. In addition to the torque and speed required by the pump, motor selection considers the available power, operating environment (e.g submersible), starting and control requirements.

Engine-driven pumps are used in emergency or standby service in the event the electrical power supply is not available.

Heating and Cooling Systems

Hydronic hot water heating systems use pumps to transfer energy from the source (such as a boiler) to the thermal load (such as a radiator). Hydronic distribution systems pump from the boiler to the radiators and back to the boiler in a closed loop. Distribution systems for heating and cooling typically include pipe or tubing, check valves, mixing valves, expansion tank, and strainers. The most common distribution systems used are primary-constant/secondary-variable flow and variable primary flow systems.

Some heating systems use steam instead of hot water. These systems use pumps to return spent steam (condensate) for reuse to the boiler. The requirements for condensate and boiler feed pumps in steam heating systems are different and need to be evaluated separate from the hot water circulation pumps.

Chilled water-cooling systems are found in many large commercial buildings to provide cooling. These systems are part of a plant that distributes chilled water to end-use cooling equipment such as air handlers, chilled beams, and process equipment.

As illustrated in Figure 1, the main components that comprise a chilled water system are:

1. Chillers that produce the cold water for circulation.
2. Condenser pumps circulate cooling tower water through the chiller condenser.
3. Primary chilled water pumps that circulate water through the chiller evaporator.
4. Secondary chilled water pumps that circulate chilled water to the cooling units
5. The hydronic distribution system that directs the moving water to the cooling units, such as fan coils, air handling units, radiant loops, and chilled beams.
6. The controls that regulate the temperature and flow rate of the chilled water.

Figure 1 – Chilled water system with winter economizer.

Centrifugal pumps are used in hydronic heating and cooling applications. The type and number of pumps depends on the size and design of the heating or cooling distribution. Centrifugal pumps are also used for condenser water pumps, and they tend to be the largest pumps used in HVAC systems. In general, for low flow (less than 50 gallons per minute [gpm]), close-coupled end suction or in-line circulator pumps are used. For higher flow rates base-mounted end suction pumps, vertical in-line pumps, or horizontal split case pumps with double suction impellers are considered. The highest flow systems (above 2500 gpm) generally use horizontal split case, double-suction pumps, and vertically suspended pumps may be used for condenser water pumps.

Plumbing Systems

Plumbing systems include pressure boosting, hot water recirculation, wastewater, and gray water. The first two deal with delivery of potable water to the fixtures at the correct pressure and temperature, and the second two deal with managing water after it has been used.

In large buildings, the public water main or other water source is incapable of meeting the pressure requirement for higher floors. Pressure boosting pumps are used in the water supply and distribution system to provide the required flow rate and pressure to all the plumbing fixtures (faucets, showers, toilets, drinking fountains, etc.) at peak and off-peak demand.

Variable-speed pressure booster pumping systems are most common in new construction, and they may be located at multiple elevations within high-rise buildings to provide the required pressure to fixtures at all floors. The variable speed capability allows for more efficient delivery of peak and off-peak flow. Figure 2 represents a pressure booster system with the following characteristics:

• Minimum pressure supplied by the city main after the water meter and back flow preventer will be 20 pounds per square inch (psig) (35 psi – 5 psi – 10 psi = 20 psig),
• Maximum system flow rate is 400 gpm
• 20 psi of system friction loss
• 25 psi of static pressure (elevation),
• The most remote fixture requires 30 psi of residual pressure.

At the maximum flow rate (400 gpm), minimum suction pressure (20 psig), and remote fixture pressure (30 psig), the pump discharge pressure would be controlled to 75 psig (30 psi + 25 psi + 20 psi), which is a boost pressure of 55 psi considering the 20-psig minimum suction pressure.

Figure 2 – Variable speed pressure booster system.

Hot water recirculation pumps are used to supply on-demand hot water to faucets at the desired temperature. This requires a properly designed and installed domestic hot water recirculation system. In addition to instantaneous hot water at any fixture, hot water recirculation reduces water consumption and wastewater costs because water is not wasted to the drain while waiting for hot water to arrive.

Wastewater and Grey water

Wastewater pumps generally transfer wastewater from toilets, and other sanitary wastewater from restrooms and lavatories, and they may also transfer other grey water generated from the building operating systems and cleaning operations to on-site or remote treatment facilities. Figure 3 shows an example of drainage that collects in a wastewater sump and is then pumped to the sewer.

Solids handling pumps are used in wastewater applications to account for the organic and inorganic solids that may be included in the liquid. The head requirements for the pumps are generally low head (less than 50 ft) since they only need to lift the liquid to the effluent piping system that flows to the treatment facility. The flow will vary depending on the size of the collection basin and the expected inlet flow, but the pump will be sized for a flow rate greater than the maximum inlet flow and will have controls to turn on and off based on the level in the collection basin.

Figure 3 – Wastewater collection system and submersible wastewater pump.

Fire Protection Systems

To protect life and property, commercial buildings are equipped with fire sprinkler systems and fire pumps. Fire pump systems are life safety equipment covered by state and local code. The National Fire Protection Agency (NFPA) publishes the standard NFPA-20, which details the design selection and installation of pumps supplying liquid for private fire protection. Fire suppression (sprinkler) systems are pressurized to respond immediately using pressure maintenance pumps.

Fire pumps used in commercial buildings are specified and installed as an assembled unit consisting of a fire pump, driver, controller, and accessories (Figure 4). Fire pump applications are one that can use a diesel engine because of their requirement to operate in an emergency and when electrical power is not available.

Rotodynamic centrifugal pumps are used most often for fire pumps in commercial applications. Positive-displacement rotary gear pumps are used for applications requiring higher pressures, such as water mist and foam ejection systems.

Figure 4 – Packaged fire pump system including controller on a skid with pressure maintenance pump.

Summary

Commercial buildings include many pumping applications as detailed in this article. There are many more applications not detailed here, such as renewables and energy recovery, chemical metering pumps used for treatment or disinfection, and swimming pool and water features pumps. The varying nature of the applications requires detailed analysis so that systems are optimally designed, pumps are properly selected, controlled efficiently and optimal comfort is provided to the occupants. For additional information refer to HI’s Pump Application Guidebook for Commercial Building Services at www.pumps.org/guidebooks.