Energy Efficient Pumps and Fans
Discussion
There are many ways to make pumps and fans work more efficiently, to conserve energy and save money.
Readings
Pumps and Fans
Pumps and Fans. Energy Saving Manual. Energy Smart
Many fan and pump systems are not run at their maximum efficiency.
Dampers, throttling valves, by-pass systems and pressure relief valves are often used to reduce output to a level that matches demand. These systems are highly inefficient.
Increasing efficiency may involve a combination of actions: trimming impellers, installing variable speed drives, improved controls or improving the efficiency of motors.
A unit of energy saved at the pump or fan saves 3.3 units at the motor, so it makes sense to start saving energy at the end of the system and work backwards.
Other benefits of increasing your efficiency include extension of equipment life, reduction of safety hazards and reduction of noise and vibration.
Energy Efficiency
Check your system to find out if any throttling valves or dampers are constantly restricting the rate of flow to 10% less than its design flow rate. If so, consider impeller trimming as this reduces energy demand (see below).
Noise and vibration may indicate efficiency problems.
The potential savings are disproportionately large - reduce your energy costs by over 80% by halving the speed of pumps or fans.
Pump Size
Centrifugal pumps are often oversized because exact pumping requirements are not known or may change over time. Therefore, it is important to optimise the system requirements before specifying pumps in a system.
Oversizing may result in a pump that is continuously throttled in order to balance the system. In such cases, a more efficient way to balance output is to trim the pump’s impeller or replace the impeller with one of a smaller diameter, or install a Variable Speed Drive on the motor.
Fan Size
It is common for most building fan systems to be oversized by an average of 60%. This represents an enormous amount of wasted energy. By appropriately resizing your fan system, you can save an average of 50 percent in fan system energy costs.
Motor Size
Replacing old motors with high-efficiency types, appropriately sized, will save large amounts of energy.
Pipe and Duct Size
Capital saved by installing undersized piping or ductwork can be a very costly false saving, as it puts additional loads on the fans, pumps and motors.
A 15% increase in pipe diameter can cut pressure drop in half. This allows the pump or fan motor to be much smaller.
Minimise the number of bends and valves in pipework to reduce energy lost to friction.
Pump Impeller Trimming
If a pump is continuously throttled to 10% less than its design flow rate, trim the impeller to reduce electrical demand by up to 25%.
Pumps appropriate for impeller trimming are those involved in a process that requires a constant flow rate, have a partially closed discharge valve, and have no process changes planned.
To take advantage of impeller trimming, use in-house or hired expertise to quantify pumping process requirements, then contact your pump distributor for impeller trimming assistance.
Fan Impeller Trimming
Impeller trimming for fans can also achieve energy savings. Altering the angle of the fan blades can reduce the load on the motor and save energy.
Turn it off
Turn off your fan or pump when it is not needed. This can be done automatically with the installation of controls.
Slow it down
The most effective way to match output to demand and to save energy is to reduce the speed of your load (i.e. pump or fan). Reducing a fan’s speed by 20% can reduce its energy requirements by nearly 50%.
Variable Speed Drive (VSD)
A VSD is an electronic device that allows the motor speed of your equipment to vary depending on actual operating conditions, rather than operating at one speed.
Varying the speed of your fans and pumps allows them to more closely match the actual load required and automatically slow down in response to reduced demand, thereby saving energy. Pumps and fans that use mechanical throttling are excellent candidates for VSD retrofits.
It is important to note that prolonged operation of an oversized motor with a VSD at very low speeds can reduce the useful life of motors and other equipment. Properly sized, smaller capacity equipment will be more suited to operation at reduced capacities.
Maintenance
Establish a regular maintenance program to clean filters.
Clean pumps and fans to ensure maximum efficiency. Accumulation of dirt or dust can decrease the efficiency of a fan by adding weight to it and increasing pressure loss in the system. Important components to clean are the filters, heating coils, silencers and fan blades.
Replace worn seals and fan blades.
Use low friction coatings on the internal surfaces of pumps to improve pump efficiency.
Ensure that drive belts are in good condition, evenly matched and correctly aligned.
2006.5.6