Efficiency of Centrifugal Fans
Years ago, the supply of energy seemed boundless and the efficiency of industrial plant was very little regarded. With the realisation that the creation of that energy, principally through the burning of fossil fuels, has contributed to climate change, plant efficiency has become the focus of governing bodies across the globe.
Industrial fans are huge energy users.
Industrial fans are estimated to consume some 25% of the energy used by the manufacturing sector and it's also estimated that 40% of that energy is wasted for a number of reasons. Inefficient fans, the incorrect selection and application of fans, poor design of fan systems and their ducting, all contribute to this massive energy loss, some of which is unwanted noise, also subject to regulation. First cost of industrial plant ruled and life cost was largely ignored. Of course, as energy has become more precious, so the cost of it has risen, so avoiding unnecessary waste has become a critical function in forward looking companies and has resulted in the creation of energy managers in many companies, whose job it is to minimise energy costs for their company. This doesn’t just mean buying the company's energy cheaper, it also means conserving it and this is best done by installing the most efficient plant as replacements and upgrades are installed and the life-cost of the plant has become an important consideration.
The European Union has become a global leader in the formulation of regulations governing the efficiency of electric motors placed on the EU market. Standard IEC 60034-30 defines the energy efficiency classes for asynchronous motors. Regulations (EC) 640/2009 and 04/2014 establish the conditions for the conversion to the new energy-efficient technology. IE2 has been in place as the minimum efficiency since 2011. January 1st 2015 saw the second stage take effect and only motors in the power range from 7.5 to 375 kW complying with Energy Efficiency Class IE3 will be permitted for line operation in the European Economic Area from that date. This is a legal requirement.
Fans too have become the subject of regulations governing their efficiency. Fan manufacturers must now comply with European Commission regulation (EU) No 327/2011 of 30 March 2011, implementing Directive 2009/125/EC of the European Parliament and of the Council with regard to ecodesign requirements for fans driven by motors with an electric input power between 125 W and 500 kW. The objective of these regulations is to achieve by 2020, an energy reduction of some 34TWhrs of electricity, corresponding to over 16,000,000 tonnes of C2.
Efficiency has long been a focus criterion in the design of every Halifax fan so the new ecodesign regulations pose no problem for Halifax Fan. As a recognised leader in the design and manufacture of efficient fans, Halifax's design personnel worked on the committee formulating these new ecodesign standards and contributed to their formulation.
The costs of inefficiency
Oversizing of fans for the job they are to undertake is a major factor in fan inefficiency. The old adage of 'make it bigger to be sure it’ll do the job' is no longer acceptable. A fan that is too big, perhaps in anticipation of future production requirements, would have to have its throughput controlled to achieve the exact needs of the process. Most often, the low-cost solution to this would be to utilise damper control to disrupt the airflow into the fan, effectively lowering its efficiency, by as much as 40 or 50%. Graph 1 shows the effect of this. The 2960 rpm fan is capable of supplying 22,000/h at 95mbar. The process requirement was actually for 65mbar and the excess 25mbar was dissipated over a damper, absorbing 80kW of power. Graph 2 shows how the application of speed control achieved the same operating condition with the damper open, the fan running at 2559rpm and only 57kW, a saving of 23kW. Extrapolate that over a working year and the energy saved by speed control is of the order of 200,000kWhrs and depending on energy costs could save as much as £20,000 per annum, not to mention the 138 metric tonnes of CO2 saved.
To ensure correct fan selection it's vital to understand exactly the pressures and flows actually required, now and in the future, without over-optimism. A fan selected fit for purpose today may not cover the need tomorrow but over-optimism of the forward requirement could cost heavily in operating terms today. Where it is necessary to start with a fan overlarge for the immediate requirement, then the most efficient means of control, variable speed of the fan, should be selected as opposed to mechanical means like inlet guide vanes or outlet dampers, which reduce fan efficiency and dissipate a great deal of energy as is shown in the two graphs.
In order to achieve the highest installed efficiency for every fan they manufacture, Halifax Fan custom designs every fan to the application only after extensive liaison with the client. For many, the process starts by accessing the selection tool on this website. This allows the client to enter the basic data that will allow the design engineers to select the basic fan model on which to base their custom design and kick-start the design process.
How Halifax Fan gets it right
Halifax Fan, like every fan manufacturer, has a number of standard ranges, from small to large, providing for high volume, high pressure, both or whatever is needed for the job. But these are merely basic templates upon which to engineer and build a custom product to meet exactly the customers’ requirements. This is why every fan that leaves Halifax’s factories in the UK and China, is a high efficiency custom built unit, designed to meet the needs of the application, manufactured from the right materials and offering high reliability and optimum efficiency and at a competitive price.
At the heart of this philosophy is an extensive and ongoing investment in design and manufacturing technology. Halifax employs the latest computer aided design software to ensure the designs translate accurately from the computer screen to the factory floor. Inventor® 3D CAD software enables Halifax to work closely with the customer, producing 3D simulation models that can be worked on together to give additional benefits, whether it’s a one-off cost saving or life-time energy savings. Whether it’s a single fan for a project or fans to be batch produced for an OEM, the same applies – the customer gets the most efficient fan for his application.