There are numerous initiatives which can help improve the energy efficiency of pumps and fans.

For information on types of pump and fan systems, see Technology Background – Pumps and Fans.

Reduce demand for pumps and fans

Large savings can be achieved by reducing the demand for the service provided by the pump or fan by optimising the system of which it forms a part. In some cases, it may be possible to eliminate the need for the fan or pump system altogether.

Some examples of opportunities in this area are outlined below.

Eliminate the need for fans and pumps

In a small number of cases, it is possible to completely eliminate a pump or fan system. Consider what service your system provides and whether the need for the service could be eliminated completely. Examples of ways to eliminate the need for a pump or fan system include:

  • Use mains pressure to deliver water into a factory by reconfiguring piping, installing appropriate valves, pressure sensors and controls. The factory-owned pumps would be used in fire-fighting mode.
  • Convert from an open-circuit system to a closed-loop system in underground mines. Converting to a closed-loop system with heat exchangers means that the incoming (descending) water provides most of the energy to raise the hot water from the bottom of the mine. The high-pressure pump usually used to pump water to the surface is no longer needed. A much smaller circulator can be used, similar to the circulators used in high-rise buildings for space-heating, hot-water and chilled-water loops.
  • Use a conveyor system or localised scrap consolidation rather than a high-velocity ducted air system to transport off-cuts and scrap as, for example, in paper product companies. This helps to save power, reduce noise and stop removing warm conditioned air from the factory. Energy mass balance analysis of ducted air systems shows that almost all of the fan input energy is used to move air rather than paper.
  • Use water, refrigerant or local heat sources to move heat rather than air-based cooling or heating systems. Using air to move heat energy necessitates moving a volume of air which is about 4,000 times the volume of water which would be required to move the same amount of heat. Systems that use water normally use a higher temperature difference than air systems and water has a higher specific heat. Both of these aspects make the ratio even higher in favour of water over air. This replacement won’t completely eliminate energy use, but the pump used to move liquid or refrigerant will require much less energy than the equivalent fan needed to deliver the same thermal power. Space requirements will also be reduced, and system components such as air filters and fire dampers are eliminated. As a smaller pipe is required, heat loss from an insulated water pipe would also be lower than from a duct at the same temperature due to the lower surface area.
  • Investigate whether the need for ventilation can be avoided by eliminating air contamination where ventilation is used to dilute or remove an air contaminant (e.g. manufacturing process modification or using alternative chemicals, closed baths etc).

Reduce the need for the service provided

Reducing the need for a service delivered by a fan or pump system reduces the energy and number of fans and pumps required. This improves the bottom line in two ways. First, it reduces operational energy costs and second, it reduces capital and maintenance costs.

Examples of demand reduction include:

  • Modifying a manufacturing or cleaning process so that less waste water is generated, reducing pumping for water transport and water treatment.
  • Reducing unwanted heat in a factory so less ventilation is required for comfort or process cooling, e.g. by lagging steam pipes or boilers.
  • Reducing the temperature of cooling air and thus reducing the quantity of air required (lower fan energy). This may result in net savings even though the refrigeration system or chiller energy consumption will increase slightly.
  • Investing in a small independent pump and fan system to replace a large centralised system. This is particularly relevant when large pumping or ventilation systems are needed to run relatively small applications at certain times of the week. For example, where a large pumping and fan system has to operate for extended hours because a small area requires after-hours ventilation, or where the pressure of a liquid pumping system is based on the high-pressure requirements of a section or machine which uses a small portion of the total flow.
  • Reducing resistance to air, gas and liquid flow through increasing duct and pipe diameters, eliminating bends or at least increasing their radius, reducing pipe and duct lengths, reducing internal friction (e.g. using smooth rigid duct rather than flexible ducting), removing restrictors and partially open valves, ensuring that pipe or duct connections do not create turbulence and keeping filters, nozzles and strainers clean.

After reducing demand for pumping and fan services, review the optimisation of the whole system to see if a smaller pump and fan can be used at a lower pressure or rate.

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Optimise the whole of system

The best way to reduce the need for the services provided by pumping and fan systems is by reviewing and re-optimising the whole system within which pumps and fans are being used. This provides an opportunity to achieve greater energy savings than improving the efficiency of the individual components in isolation.

The overall efficiency of the existing fan or pump system can be calculated by comparing the input energy and the minimum amount of energy which is theoretically required to provide that service. The ease with which this can be done will depend on the complexity of the system and the existence of meters, design and equipment documentation.

For example, it is possible to calculate the system efficiency where a pump lifts water from a pit to a tank with a known height above the pit. There is a constant flow of water into the pit, but the pump is turned on and off by a float switch. Measuring the rise in liquid level and the time taken for that rise while the pump is off, and measuring the cross-sectional area of the pit, allows the inflow rate to be calculated. The pump control board has an electricity meter which shows both instantaneous power (kW) and total energy (kWh). Dividing the theoretical energy requirement to lift the total water moved in a period of time with the metered energy gives the overall system efficiency.

Physical design aspects of the systems that pumps and fans operate within, not associated with the pumping mechanism, can also have significant effects on overall system efficiency. For example, the motor, drive and pump or fan are part of the same system. They need to be matched, as the characteristics and performance of one component will affect the others.

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Conduct an equipment survey and assessment

It is difficult to manage fans and pumps systems and their energy use unless there is information available on their controls, function and maintenance requirements.

To assist the optimisation of existing pump and fan, a register of fans and pumps can help facilitate:

  • identifying energy efficiency opportunities
  • planned, preventative maintenance
  • documenting the service provided
  • documenting the equipment installed and measurements undertaken.

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Install metering and monitoring

On-going monitoring and maintenance of pump and fan performance is critical to ensure the most efficient operation possible.

Electricity metering is needed to track equipment energy consumption but this does not always mean that new meters must be supplied and installed. Where a fan or pump motor is supplied via a variable speed drive (VSD), in most cases energy metering is built into the VSD itself. Accumulated energy consumption may be read off the VSD display or energy data extracted automatically via the VSD high level interface by a supervisory control and data acquisition (SCADA) or building automation system (BAS). In addition, some recently released circuit breakers have in-built energy metering which is applicable for new installations.

Switch off systems when they are not required

Energy can be easily saved by consolidating the operating times of pumps and fans with the times that the fan or pump service is required.

Determining correct operating hours might be investigated by:

  • Reading hour-run meters at regular intervals (e.g. weekly)
  • Dividing hour-run meter readings with the total time the system has been installed
  • Comparing energy (kWh) and power (kW) readings where the drive motor has a dedicated multi-function electricity meter
  • Examining electricity meter load profiles
  • Checking control settings (e.g. time-switches, automatic control programs in building automation system (BAS) or supervisory control and data acquisition (SCADA)
  • Using existing automatic control systems, time-switches and well-managed manual procedures.

Following these procedures can help to ensure that a fan or pump will be automatically switched off when the machine, or the system it is part of, is not running.

Adjust pump or fan speed

Many fans and pumps with variable speed drives (VSDs) are run continuously at or near full speed. Despite making the investment, most of the potential benefits of a VSD will not be realised unless a control strategy has been implemented to reduce the fan or pump speed.

When a control signal is connected to the VSD, it should be commissioned or adjusted to ensure that energy savings are maximised. To achieve satisfactory service and energy savings determine the role of the fan or pump, decide on an appropriate control signal and set-point, and adjust the settings.

This is likely to involve progressive and iterative improvements in order to arrive at the optimal control strategy.

For more information on VSDs, see Install variable speed drives.

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Reduce friction losses

The energy consumption of fan and pump systems can be reduced by minimsing or eliminating any excessive resistance which those systems work against. This can also extend equipment life, reduce noise and allow the selection of lower capacity fans, pumps and motors.

Opportunities to reduce the friction losses by optimising existing systems include:

  • Eliminating unnecessary flow paths
  • Improving duct design
  • Straightening flexible ducts
  • Keeping pipes and heat exchangers clear of fouling, sludge and corrosion.

In a fan system, ensure:

  • Dampers work correctly (don’t close more than required)
  • Filters used are a low resistance type (and larger filters have lower resistance for a given flow rate)
  • Coil surfaces are kept clean
  • Ductwork internal surfaces are inspected and kept clean (note that cleaning can cause damage to ducts, creating leaks, so performance should be checked after cleaning).

In a pump system, ensure:

  • Valves do not stick
  • Strainers are regularly checked and cleaned
  • Released gases are effectively removed
  • Water treatment chemicals are employed
  • Water samples are taken to monitor early signs of internal corrosion.

Use the most efficient pumps and fans

Many pump and fan systems have multiple pumps and fans. At least one is intended for one duty, and used most of the time. Others are for standby, and are used for unusually high loads.

Existing procedures may mean they are either randomly selected or swapped regularly. However, if one set is more efficient than the other, then it could be run as a preference to reduce energy consumption.

Even pump or fan and motor sets which appear identical can have significantly energy efficiencies. Determining the efficiency for a given duty will entail measuring the flow rate and head delivered, as well as the electrical energy consumed.

Implement preventive maintenance

A planned, analytical maintenance program will reduce total costs of owning and operating fan and pump systems by reducing interruptions to production, reducing energy waste through increased resistance, reducing major repairs and extending equipment life. It should also improve reliability and reduce down-time.

Steps to ensure fan and pump systems are well maintained include:

  •  adjusting seals, glands and seals packing to match manufacturers’ specifications and ensuring gaskets and seals do not interfere with smooth flow
  • monitoring bearing condition (e.g. noise, heat, vibration), lubrication and replacing as required
  • monitoring pump wear to guard against declining efficiency
  • cleaning strainers, filters and pipes to minimise resistance to flow
  • cleaning/clearing pump and fan impellor and casings of obstructions, dirt and corrosion
  • repairing air and liquid leaks (apart from glands or seals which are intended to seep)
  • checking and fixing air obstructions, such as closed fire-dampers, squashed flexible ducts and disconnected or torn flexible ducting
  • checking the alignment of motors and drives and ensuring bolts, fastenings, the shaft key and the fan impellor are secure
  • maintaining motors and drives.

Install optimum new pump and fan systems

Investing in new efficient pump and fan systems provides the opportunity to achieve large energy savings and to minimise total life-cycle costs.

System changes might be triggered by changes to manufacturing processes, increasing or decreasing flow rates, equipment wear or failure or lack of spare parts. Even without these triggers, the potential energy savings justify investigating upgrades or replacement of an existing, functioning fan or pump system.

Further fine tuning through eliminating unnecessary flow paths, reducing excessive frictional losses, improving inlet and outlet conditions and maintaining performance can also save energy.

Some examples of opportunities in this area are outlined below.

Select an appropriately sized pump or fan

Significant energy savings can be achieved if a pump or fan is chosen to serve the requirements of a particular application at a lower speed.

Often, when selecting a pump or fan for a new or replacement application, organisations tend to select a larger piece of equipment to allow for uncertainty. While some modest over-sizing is generally acceptable, gross over-sizing should be avoided. Rather than replace ‘like for like’, check whether the original equipment was appropriate by calculating the flow rate and pressure required. This will avoid repeating a previous mistake.

Each pump or fan, when operating at a fixed speed has a predictable ‘pressure versus flow rate’ relationship which is available from manufacturer’s documentation. Once known at one speed, this relationship can be accurately predicted at other speeds. Instrumentation is commonly used to measure flow rate and pressures. Alternatively, flow rate can be estimated using measured differential pressure and pump performance curves.

Install the highest efficiency pump or fan available

Reputable pump and fan manufacturers publish pressure versus flow curves (graphs) which include efficiency lines. Once the required duty is known, a key selection aspect should be the ability to achieve a high operating efficiency.

For example, take a scenario where the design duty for a fan selection is 50,000 L/s (50 m3/s) at a total pressure of 1500 Pa (1.5 kPa). This equates to an ‘air power’ requirement of 75 kW. If Fan A has an efficiency of 0.5 (50%) it would require a motor with an output of 150 kW. By contrast, if Fan B has an efficiency of 0.75 (75%) it would only require a motor with an output of only 100 kW.

The efficiency of pumps and fans varies markedly, usually being highest around the middle of the indicated operating range. The type of fan technology chosen also contributes to the level of energy efficiency.

For information on types of pump and fan systems, see Technology Background – Pumps and Fans.

Install controls

Most industrial systems have pumping requirements with several operating points or variable flow and pressure requirements. Picking the pump or fan with the optimum efficiency for a specific duty is only part of the story. The other part is controlling the flow rate to match the process requirements. You can do this in several ways:

  • Recirculation – continuously runs the fluid round the system through a buffer tank
  • Throttle control – uses valves or flaps to control the flow rate
  • Cycle control – turns the pump on and off to control the flow
  • Variable speed drive – controls the pump’s speed to control the flow.

The most efficient control option is usually achieved through variable speed drives.

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Install variable speed drives

An electronic variable speed drive (VSD) varies the frequency of the AC electricity supplied to an induction motor to reduce its speed. The most common applications for VSDs are pumps and fans.

The volume of air flowing through a fan or liquid flowing through a centrifugal pump is proportional to the speed of the pump or fan, but the electrical power required is proportional to the cube of the speed of the pump or fan.

A VSD has the potential in some fan and pump systems to:

  • Cut energy use significantly (the amount will depend on the variability in demand and the degree of over-design or over capacity)
  • Reduce peak electrical power, and possibly overcome problems with circuit capacity, with a soft-start feature
  • Improve power factor, depending on the specifications of the VSD
  • Reduce noise
  • Reduce wear on valves.

Identifying potential to use a VSD
Signs that a VSD may suit your pump system include:

  • throttling valve or automatic throttling controller which is partially closed
  • A liquid bypass line with the bypass valve at least partially open
  • The pump starts and stops frequently (e.g. under the control of a float switch or pressure controller) and/or operates for only some of the time the system is enabled
  • There is evidence of excessive flow (e.g. pipes shaking, cavitation, noise, overheating)
  • The flow rate requirement is expected to vary significantly over time.

Signs that a VSD may save energy in a fan system include:

  • There is a downstream throttling damper
  • Inlet guide vanes are used to reduce airflow rate and are partially shut
  • Flow rate requirements are expected to vary significantly.

Selecting a VSD
Selecting a VSD is not an exercise in looking at lowest cost products as this will not achieve the best result. This is because most fans and pumps are designed to work with systems that exhibit a quadratic load characteristic, meaning the pressure generally varies in a square law relationship with the flow rate. So, the most effective VSD will be one that has been designed specifically for a given quadratic load application.

Loads vary over time. The motor needs to be sized to satisfy the maximum load, but the motor speed can be varied in order to match the load at non peak times. Varying loads include:

  • Pumping – where the volume to be pumped varies, e.g. from changes in production or product mix, rainfall, or a greater need for filtration or water treatment
  • Cooling – which requires higher airflow during warmer weather
  • Ventilation for dilution – which needs to be higher in response to higher occupancy or more vehicle movements.

Installing a VSD
When installing a VSD to take over the flow control function of a throttling valve, consider removing the existing valve.

Where the cost of a VSD cannot be justified, multi-speed motors may offer sufficient flexibility to deliver useful savings; but it needs to be confirmed that the efficiency remains high at each speed. Such expenditure is justified as VSDs do bring significant energy savings.

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Use appropriate motors

Many modern, high-efficiency motors often have a slightly better efficiency at reduced load compared to full load. This suggests over-sizing of the motor may not be a large issue. Excessive over-sizing should be avoided however due to the increase in associated motor and infrastructure costs (e.g. contactors, cabling and variable speed drives).

Consideration should also be given to whether older equipment may still be using inefficient motors. When replacing existing motors or specifying motors for a new system, the most common type specified is the induction motor. In a low-speed application, an induction motor may be a poor selection. This is because it has a low power factor, meaning a higher current draw for the same delivered power. One alternative is a permanent magnet motor which is usually a better selection because it has similar or higher efficiency, and a much higher power factor (lower current draw).

The most efficient way of transferring motor shaft power to a pump or fan impellor to achieve hydraulic power is by direct drive. This means the motor is directly coupled to the impellor shaft so that the impellor speed is the same as the motor speed. Associated components, such as belts, gearboxes and chains, all absorb or waste some power. They also increase maintenance costs, reduce reliability and present an additional safety hazard. Where the impellor speed requirement is below 600 rpm, consider a permanent magnet motor rather than an induction motor. Where indirect drives are necessary, ensure losses are minimised by appropriate adjustment and regular maintenance.

For fans, the motor can be built onto the impellor to achieve a more compact form factor which is useful where space is at a premium.

At present, most ECDC motor driven pumps and fans have small capacity, suited to situations such as fan-coil units and domestic hot water circulating pumps, with motors up to several kW.

See the Motors and Motor Systems technology page on the EEX website.

Fine tune pump and fan applications

Fine tuning your pump and fan applications helps you achieve improved efficiencies and savings. You can use several low-cost measures or minor modifications to fine tune your pump and fan system performance. Generally, these can be implemented with only minor interruption to processes. The easiest options to implement include:

  • eliminating unnecessary flow paths
  • reducing excessive frictional losses
  • improving inlet and outlet conditions
  • maintaining performance
  • ensuring pumps and fans run in parallel are not run excessively (operating excess pumps increases flow and friction losses, adding to energy consumption).

For more information