Specific Fan Power (SFP)

Quantify the energy efficiency of fan coil units and other air movement systems by understanding the influence of specific fan power.


Specific Fan Power (SFP)

One of the key influencing factors affecting the ventilation market is Specific Fan Power (SFP) figure, specifically a low SFP.

Specific Fan Power (SFP) is a parameter that quantifies the energy-efficiency of fan air movement systems. It is a measure of the electric power that is needed to drive a fan (or collection of fans), relative to the amount of air that is circulated through the fans. It is not constant for a given fan, but changes with both air flow rate and fan pressure rise. The SFP principle in fan selection is to choose a fan to deliver one flow at one pressure in a particular system using as less electrical energy as possible and all other factors being equal.

For such a system to be effective, certain good practices should be followed. For a system to be worthwhile, for example in MVHR units, the heat reclaimed should far outweigh the energy used to power the fans.

Within a fan coil system, fans are arranged with a heating or cooling coil and ducting arrangement to provide heating, cooling & ventilation, typically within offices and working areas. When new buildings are specified, stringent targets are put into place to ensure all energy consumption is kept to a minimum, ensuring buildings comply with “green targets” and work efficiently.

For MVHR the lower the SFP the letter as this relates to the electrical efficiency of the fans. Some systems can get as low as 0.5w/l/s.

A key factor is the fan-motor combination. Energy efficient fans are invaluable in helping to provide the best efficiency, so the SFP figure is the measure used for comparison. More often than not utilising a low slippage high efficiency EC motor and drive combination is the key to achieving the highest efficiency.

Typically, ventilation units such as fan coil units or heat recover units use between two and five fans to allow each fan to be run at lower speeds which has several benefits:

The efficiency of the unit can only be maintained if fans are all running together at their desired operating points. When a fan fails the other fans must then speed up to pick up the duty. With this in mind we can appreciate the importance of monitoring fan units for fan failures. The Ecofit M41-A5 from Axair has on board failure monitoring, this benefit is an add on for other manufacturers making the unit a cost effective and effective choice when installing this type of application.

The most popular option for fan coil monitoring is a taco output, which generally come as standard with most manufacturers EC motor ranges. The problem with using taco monitoring is that multi-fan systems within a plenum arrangement are systems of two halves. The inlet side is under a constant low pressure and the discharge side under constant high pressure. As soon as a fan fails and begins to slow down, the taco pulse also slows until the unit stops and runs in reverse. Taco monitored systems will not show fan failure until either the motors are locked, there is a complaint that the unit has lost performance or there is too much noise as one or more fans run full speed to try and pick up the duty lost when most of the fans are failed, causing an inefficient system and high noise levels.

The use of the SFP approach in the fan selection process will result in a quieter, more efficient, and more reliable system.

How can Axair help?

Axair Supplier partner Ecofit, has developed a double inlet, centrifugal fan EC fan, the GDS G9 133×190, which not only features a highly efficient EC motor, surpassing ERP 2013 and 2015, but also has a built-in failure monitoring system to detect failures of individual fans or failures of fans within a deck. The failures are monitored via a normally closed contact within the motor which is calibrated to open when the fan speed drops below 200RPM or in the instance that the motor comes to a stop, the monitoring circuit is opened. The management system will detect as a fan failure this can then be serviced more effectively.

Contact us for more information on how Axair can assist with Fan Coil application efficiency or any other project on 01782 349430.

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