SAIRAC October tech talk topic: Axieco fans

The following is a presentation delivered at the SAIRAC Johannesburg centre by Francois Schoombie (N.Dipl. Mech Eng. TUT), technical manager and EC product specialist for ebm-papst, during August.

Tough ambient conditions prevail in the ventilation, air conditioning and refrigeration sectors, as well as in mechanical engineering. To cope with these applications effectively, you need electrically and mechanically robust solutions that also work at a high level of efficiency.

AC axial fans that have been widely used up until now will reach their limits in this contentious area by the time the next stage of the ErP comes into force. The EC range of AxiEco Protect and AxiEco Perform duos, are a series that perfectly adapts to these requirements.

ErP stands for Energy-related Products. It is a European Union directive that sets minimum energy performance standards for heating and cooling products, including air conditioners, heat pumps and boilers. The ErP directive aims to reduce energy consumption, improve energy efficiency and reduce carbon emissions. Some examples of affected products are fans, electric motors, pumps and compressors. There are other standards and regulations, such as ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) and FER (Fan Energy Rating).

The ErP Directive was implemented in phases over five-year intervals. The first phase started in 2011, when the minimum efficiency standards were set. In 2015, ±30% of fans did not meet these standards and were no longer allowed to be sold within the EU market. The ErP Directive initially applied to individual components, such as fans, pumps or compressors. Later, it expanded to cover the whole unit and systems that use these components and introduced new efficiency metrics and requirements.

Supplied by ebm-papst

In South Africa, there is a growing interest in energy efficiency and green building awareness, especially in the context of rising electricity costs and environmental concerns. However, there is  still a lack of standards and regulations in South Africa to enforce these practices. Some experts and stakeholders have been advocating for energy efficiency since 2007 and have shown the potential savings and benefits of adopting more efficient products and systems. Therefore, there is a growing demand for more education and implementation of similar initiatives in South Africa.

This ErP implementation in EU countries has had a huge impact on the whole industry, not just the suppliers. These standards also meant that any product that needed to be replaced had to comply with the current efficiency requirements. For example, if you had an air-conditioning unit with a fan or a compressor that failed, you could not replace it with the same model if it did not meet the standards.You would have to find a more efficient product instead. This increased the demand for more energy-efficient products, which in turn reduced energy consumption and carbon emissions in the long run. According to some estimates, the ErP Directive saved some ± 20 million tons of CO2 emissions since 2012. These figures are based on the EU market, but similar standards and regulations are also followed by other countries and regions, such as the US and ASHRAE. Therefore, the ErP Directive has a global influence on the eco-design of ALL energy-related products.

The ErP Directive is a mandatory requirement for the European market, and it influences the product selection and replacement decisions of the customers and suppliers. In South Africa, however, there is less incentive and awareness to choose more efficient products, even though they can save energy and money in the long run. The suppliers and contractors often prefer to sell cheaper and readily available products, rather than premium and compliant ones. This is a short-sighted approach that ignores the long-term implications of energy efficiency and environmental impact. Determining whether a fan conforms to the ErP regulation – this involves assessing the efficiency of the fan as a whole, i.e., the entire unit comprising control electronics (if fitted), motor and fan impeller. It is based on the ratio of air flow to power consumption. The higher the overall efficiency, the more efficient the fan. The ErP Directive sets minimum Efficiency values for different types of fans. Refer to graph:

Supplied by ebm-papst

There are different kinds of fans, such as axial fans and centrifugal fans. Axial fans have a hub and blades that rotate around an axis. The air enters and exits in the axial direction. Centrifugal fans have blades that curve outwards from the hub. The air enters in the axial direction and exits at a 90-degree angle (centrifugal forces). Depending on the application, you need different fans for different purposes. Axial fans are usually used for low-pressure applications, such as in the HVAC&R industry.

Centrifugal fans are used for higher-pressure applications as also found in the HVAC industry, namely for Air Handling Units (AHUs). The power absorbed by a fan is measured by its pressure and volume flow rate. Axial fans have a region where the pressure drops and then rises again. This is called the stall or saddle region, which is dependent on the fan geometry, blade angle and speed. In this condition, the fan is rotating but not delivering the full potential of air flow. The pressure is mainly determined by the velocity component, which is why we design the ducts with specific velocities.

If there is turbulence within the (suction) airflow path, this disrupts the pressure balance and causes noise. This is typically in the range of 250 to 500Hz. Higher frequencies are always easier to attenuate. A conventional axial fan without a rotating diffuser, has high velocity regions near the blades and a large recirculation zone behind the fan. This reduces efficiency and increases noise. A fan with a rotating diffuser has lower velocity regions and a smaller recirculation zone. An optimised design with a rotating diffuser has more uniform velocity distribution and minimal recirculation. This improves performance and reduces noise. Air-Throw within your typical application.

Aother benefit of the rotating diffuser design is the increased rigidity thereby allowing the impeller to rotate at a higher rpm without deformation. This gives us more power density, which means we can use a smaller fan with higher RPM and get better performance and efficiency. This is useful for applications where optimal air-flow designs are necessary. In the past, you could not use axial fans for these applications, but now we have a solution that can meet all your requirements.

HOW EC MOTORS DIFFER FROM AC MOTORS

EC is an abbreviation for electronically commutated, which means that these motors deliver higher efficiencies than the conventional AC type. Refer to Graph:

Supplied by ebm-papst

DC motors are easier to speed control by fluctuating the voltage, and they are more efficient than AC motors in terms of electrical input power versus shaft output power. AC motors were the most common type of motors that we used, and they work by supplying alternating current to the windings that create an electromagnetic field. This field induces a secondary magnetic field within the rotor, and the relative movement of these fields causes the rotor to spin. The frequency of the AC power determines the speed of rotation. To use a DC motor, one needs to convert the AC power into DC power, which is all integrated within our EC motors. There are also other advantages of EC motors, such as Modbus communications and built-in protection devices.

FAN AERODYNAMICS

Each one of the individual components has a role to play in the overall performance of the fan. If we look at only the motors, we would have heard about IE ratings. The conventional AC motors used in the past were IE1 or IE2. Nowadays, we can go up to IE4 and higher. The efficiency of a fan is the ratio of what we get out vs what we put in. We put in electrical power and we get out air movement. The air movement can be measured in kilowatts if we use the formula: volume (in cubic meters per second) x pressure (in Pascals). This is the ideal power required to move air, without considering any losses. But in reality, the fan has many individual components that contribute to such losses, such as the motor windings, belt drives, bearings and overall aerodynamics of the impeller itself. For example, if we put one kilowatt of electrical power into the motor, we don’t get one kilowatt of shaft power out of it. The motor has an efficiency rating that tells us how much power it can deliver to the shaft. As an example, if we buy a standard 3kW IE2 motor, it has an efficiency of ±86%. If we buy a premium IE4 motor, it has an efficiency of ±88%. This means that for every kilowatt of electrical power we put in, we get 0.86 or 0.88kW of shaft power out. The same principle applies to the other components of the fan. So, to calculate the overall efficiency of the fan, we need to consider all such factors and losses.

To accurately calculate the overall efficiency of a fan, we cannot simply use the catalogue data of maximum efficiency for individual components. We need to adjust the efficiency of the various components according to the actual performance of such, within the duty point.

This is done by applying the correction factors from ISO 12759. For example, if we assume that the fan and the motor are both 86% efficient based on the catalogue data, we are totally wrong. The actual overall efficiency of the fan is only 58%. So, if I want to sell you a fan that is 2% more efficient, but you have to pay 10% more, how can I ever convince you? The best and most accurate way to determine the fan efficiency is to measure it physically. We need to measure the electrical input power and the air output power and divide them by each other. However, this is not always easy in the installations or design phase. That’s why we use these calculations to obtain accurate results.

Globally and locally, ebmpapst can assist with selecting the most efficient fans, as well as providing detailed Life Cycle Cost calculations. Please contact your nearest office for any further assistance.