Date: 2025-10-24 22:28:08
By Nicholas Popp
In Zurich, Switzerland, a university hospital was operating with an older ventilation system powered by a single large double-inlet, belt-driven fan. One day, the fan failed, leaving the hospital without airflow. Faced with an urgent need to restore ventilation, the hospital began evaluating its options.
One possibility was to replace the failed unit (Photo A) with a similar belt-driven fan. This configuration allows for flexibility in motor placement and speed adjustment. Typically, the motor is mounted separately from the fan, transmitting power to the impeller through the belt-and-pulley system. Belt-driven fans come with notable drawbacks, however, as they tend to be relatively inefficient because of mechanical losses from belt slippage (especially when their belts are not tensioned properly); energy loss in the form of heat resulting from friction between belts, pulleys, shafts, and bearings; and energy loss at points of mechanical transfer. Additionally, the fans require regular maintenance and periodic replacement of worn components, such as belts and bearings.
An alternative to belt-driven fans are direct-driven fans. With a direct-driven fan, the motor is connected directly to the impeller; with no belt-and-pulley system, maintenance is less and efficiency higher compared with a belt-driven fan. When a standard alternating-current (AC) motor is used, speed control is lacking, unless a variable-frequency drive (VFD) is added. While VFDs enable speed control, they increase complexity and require additional space.
Electronically commutated (EC) fan arrays represent an innovative solution. EC motors are compact and highly efficient, with built-in electronics enabling precise speed control. These motors typically use permanent magnets and can achieve efficiencies of 80 to 90 percent, with some achieving efficiencies as high as 96 percent. Rather than a single large fan, multiple small fans arranged in an array are utilized. Combined, the fans can match or exceed the performance of a traditional belt-driven fan while offering additional benefits. Increasingly, commercial and industrial facilities are being retrofitted with EC-fan arrays. This article examines the case of the Swiss hospital.
Swiss Hospital’s Solution
Traditional belt-driven fans often are oversized or undersized. Oversizing a fan can result in additional costs, wasted energy, excessive noise, and uncomfortable drafts, while a fan that is undersized or that becomes undersized as a facility expands can be overworked, leading to increased maintenance and energy costs, reduced system lifespan, and inadequate air circulation with hot and cold spots. With an EC-fan array, fans can be individually speed-controlled and programmed to meet exact airflow requirements, allowing the system to maintain consistent and comfortable indoor conditions by adjusting to seasonal changes and scaling airflow for facility expansions. Figure 1 illustrates differences in air velocity between a single large fan (left) and an array of eight smaller EC fans (right).
An EC-fan array distributes air more evenly than a traditional belt-driven fan does, resulting in more homogenous air distribution, reduced noise, and improved thermal comfort. In the case of the Swiss hospital, the required duty point (airflow and pressure) was 20,282 cfm (34,460 m3/h) at 1.53 in. wg (380 Pa). This was achieved using an array of four EC fans (Photo B).
PHOTO A. Swiss hospital’s belt-driven fan.
Energy and Carbon Emissions
The Swiss-hospital retrofit resulted in not only optimized airflow but a reduction in the building’s carbon footprint. Because EC motors are highly efficient, they consume less energy, which directly translates to lower carbon-dioxide (CO2) emissions. As of 2023, U.S. CO2 emissions can be calculated using 0.81 lb (367 g) of CO2 per kilowatt-hour.1 The Swiss hospital saw an energy savings of 66,559 kWh per year, which translates to a reduction in CO2 emissions of 24.43 tons per year:
FIGURE 1. Air velocity with one large fan (left) and eight smaller fans (right).
Indoor-Air Quality
With older belt-driven systems, inadequate maintenance of belts and pulleys can cause the release of fine particulates, which can circulate through ductwork and compromise indoor-air quality (IAQ). For critical applications such as hospitals, cleanrooms, and schools, additional filtration solutions may be needed, leading to increased costs and maintenance. Being direct-driven, EC fans avoid this concern.
Return on Investment
While the initial cost of an EC-fan array may be higher than that of a single AC belt-driven fan, the long-term cost savings often more than compensate for the difference. EC-fan arrays are highly energy-efficient, which leads to a significant reduction in operating costs over time. Although savings can vary depending on the application and system design, a return on investment typically is achieved within five years. In addition to energy costs, maintenance expenses are reduced, as there are no belts to adjust, replace, or maintain.
In the case of the Swiss hospital, the cost of replacing a single large fan with a four-EC-fan array was $32,490. With the newly upgraded system, the hospital’s annual power consumption dropped from 86,566 kWh to 20,007 kWh and its annual energy costs from $13,816 to $3,193, a savings of $10,623 (77 percent). Coupled with annual maintenance savings of $912, the total annual savings was $11,535. The hospital was able to recoup installation costs in under three years and will continue to save on energy for years to come (Figure 2).
Additional Benefits
A challenge of using a single large fan, a belt-driven model in particular, is the space the fan requires. Such a fan typically demands a substantial footprint for both operation and maintenance access. What’s more, installation/replacement often requires cranes or other specialized equipment, adding complexity, time, and cost. In contrast, EC fans are compact and lightweight; typically, they are small enough to fit through standard doorways and elevators and light enough to be carried by two people, making installation faster, simpler, and more cost-effective. Many retrofit projects can be completed in just a few days, with some able to be completed in a single day. In the case of the Swiss hospital, installation was completed by two people in four working days.
PHOTO B. Swiss hospital’s EC-fan array.
FIGURE 2. Swiss hospital’s energy costs over time.
Another advantage of using EC-fan arrays is the ability to design redundancy into a system. Engineers can design systems using the N+1 redundancy principle, meaning include one more fan than is necessary. If one fan in the array fails, the remaining fans can increase their speed to maintain the required airflow, ensuring continuous operation with no downtime. A single-fan system has no such backup—if the fan fails, airflow is completely lost, as was the case with the Swiss hospital.
Lastly, EC fans are easy to stock and replace. Facilities can keep spare units on hand, enabling quick swaps in the event of a failure.
Regulatory Landscape
As energy efficiency and environmental sustainability become greater priorities, fan systems are becoming increasingly regulated. Although a regulatory gap exists at the federal level, individual states are creating their own energy-conservation standards. A leading example is California with its Title 20 appliance-efficiency regulations.2 Title 20 adopts the U.S. Department of Energy (DOE) test procedure for fans and blowers;3 establishes a single fan-energy-index (FEI) requirement of 1.0 or greater for all applicable fans and blowers sold or offered for sale in California, regardless of class; requires fans to be listed in the Modernized Appliance Efficiency Database System (MAEDbS); and mandates proper labeling and documentation. The FEI metric has been adopted for other codes and standards, such as ANSI/ASHRAE/IES Standard 90.1-2022, Energy Standard for Buildings Except Low-Rise Residential Buildings, and the 2024 International Energy Conservation Code (IECC),4 to promote energy-efficient fan systems. These developments are pushing the market toward retrofitting older systems with high-efficiency technologies, such as EC-fan arrays.
Summary
While the initial investment in EC-fan arrays may be higher than that in traditional belt-driven systems, the long-term benefits are undeniable. Facility owners can expect to see significant energy savings (in the case of the Swiss hospital, a 77-percent reduction in annual energy consumption), a rapid return on investment (often within just a few years), simplified installation and reduced maintenance, built-in redundancy that prevents unwanted downtime, improved airflow distribution, and greater occupant comfort.
In addition to offering performance improvements, EC-fan arrays are well-aligned with today’s increasingly stringent regulatory and environmental standards. EC-fan arrays not only meet evolving standards, they help facilities stay ahead of them. In a world in which energy efficiency, resilience, and environmental responsibility are essential, EC-fan arrays offer a smart, scalable, and future-ready solution.
References
- U.S. Energy Information Administration. (n.d.). How much carbon dioxide is produced per kilowatthour of U.S. electricity generation? Retrieved from https://bit.ly/FAQ_CO2
- California Office of Administrative Law. (n.d.). California code of regulations. Retrieved June 16, 2025, from https://bit.ly/Title20
- U.S. Department of Energy. (2023, May 1). Energy conservation program: Test procedure for fans and blowers. Federal Register. Retrieved June 16, 2025, from https://bit.ly/DOE_CIFB
- International Code Council. (2024). 2024 international energy conservation code (ch. 4). Retrieved from https://bit.ly/IECC_Ch4
About the Author
Nicholas Popp is research-and-development engineer, standards and regulations, ventilation division, for Ziehl-Abegg. Focused on product compliance with industry standards, regulations, and quality requirements, he is actively involved with Air Movement and Control Association (AMCA) International and works closely with nationally recognized testing laboratories, such as UL. He has a degree in mechanical engineering from the University of Central Oklahoma.
Air Movement and Control Association International, Inc.