Energy Savings from EC Fan Retrofit

Keywords: EC fan, fan retrofit, air handling unit, energy efficiency, fan array, HVAC energy savings

This case study presents an energy retrofit of an existing air handling unit in a healthcare facility. A belt-driven centrifugal fan was replaced with an EC fan array. Measured test and balance data were used to evaluate system performance and quantify energy savings while maintaining the required airflow and system pressure.

Introduction

Ventilation systems represent a major share of energy consumption in healthcare and commercial buildings. Air handling units (AHUs) frequently operate continuously in order to maintain indoor air quality, temperature control, and pressure relationships in occupied spaces. In many existing installations, supply fans are driven by conventional alternating-current (AC) motors connected to centrifugal fans through belt drives.

Although belt-driven systems are reliable and widely used, their overall efficiency may be limited due to mechanical losses in the belt transmission, motor efficiency limitations, and reduced performance at part-load conditions. Over time, belt wear and misalignment can also decrease fan efficiency and increase maintenance requirements.

Energy retrofits of ventilation systems offer an effective opportunity to reduce electrical consumption while maintaining required airflow and pressure conditions. One increasingly common retrofit approach is the replacement of traditional belt-driven centrifugal fans with electronically commutated (EC) fan arrays. EC fans combine high-efficiency brushless motors with integrated electronic speed control and direct-drive operation.

This configuration eliminates belt losses, simplifies maintenance, and can significantly improve fan system efficiency. EC fan arrays also provide improved controllability and operational flexibility, which can benefit ventilation systems operating under varying load conditions.

This article presents a practical case study of a fan retrofit implemented in an existing air handling unit serving a healthcare facility. The retrofit replaced a belt-driven centrifugal fan with an array of EC plug fans installed within the existing fan section. Performance of the original system was determined using measured test and balance data, allowing a direct comparison between the existing and retrofitted configurations.

Existing System Description

The investigated system was an air handling unit installed in a rooftop mechanical room serving a healthcare facility. The AHU supplied ventilation air to a rehabilitation area.

The unit was equipped with a belt-driven centrifugal supply fan powered by a three-phase AC motor. The motor had a rated power of 5 horsepower (HP), equivalent to approximately 3.7 kilowatts (kW), and fan speed was controlled using a variable frequency drive (VFD).

The fan was connected to the motor via a belt-and-pulley transmission system. While common in older air-handling units, such systems introduce mechanical losses and require regular maintenance, including belt inspection, tension adjustment, and periodic replacement. The existing belt-driven fan installed in the air handling unit is shown in Figure 1.

Figure 1. Existing belt-driven centrifugal fan installed in the air handling unit.

Test and balance measurements were used to determine the actual operating conditions of the system.

The design airflow of the air handling unit was: 8,647 m³/h

Measured airflow during testing was: 7,828 m³/h

The measured total static pressure across the fan was: 585 Pa

Electrical measurements indicated an average supply voltage of approximately 205 volts (V) and a measured motor current of approximately 9.4 amperes (A) with a power factor of approximately 0.85. Using the standard three-phase power equation:

P = √3 × V × I × PF the electrical input power of the existing fan system was estimated to be approximately: 2.84 kW

This value was used as the baseline power consumption for evaluating the retrofit.

Retrofit Solution

To improve the energy performance of the ventilation system, the existing belt-driven centrifugal fan was replaced with an electronically commutated fan array installed inside the existing air handling unit.

The retrofit system consisted of three EC plug fans operating in parallel. Each fan includes a high-efficiency EC motor with integrated electronic speed control and direct-drive impeller design. The EC fan array installed in the air handling unit is shown in Figure 2.

Figure 2. EC fan array installed in the air handling unit.

The fan array was designed to operate at the same system operating conditions determined by the test and balance measurements.

Operating point: Airflow 7,828 m³/h Total static pressure 585 Pa

At these operating conditions, the total electrical input power of the EC fan array was calculated to be approximately: 2.14 kW. This represents the combined electrical input power of the three EC fans operating together.

The EC fan retrofit also eliminated the mechanical belt drive system and simplified the overall fan assembly. The fan operating point corresponding to these conditions is illustrated in Figure 3.

Figure 3. Fan operating point showing airflow 4,606 CFM (7,828 m³/h) at total static pressure 2.35 in.w.g. (585 Pa).

Energy Performance Analysis

The energy performance of the existing and retrofitted systems was compared using measured operating conditions from the test and balance report.

Electrical input power of the existing fan: 2.84 kW

Electrical input power of the EC fan array: 2.14 kW

The reduction in electrical power demand is therefore: 0.70 kW

This represents approximately: 25% reduction in fan power consumption

The electrical power comparison between the existing belt-driven fan and the EC fan array retrofit is presented in Figure 4.

Figure 4. Electrical power comparison between the existing belt-driven fan and the EC fan array.

For energy analysis, the ventilation system was assumed to operate continuously throughout the year, which is typical for healthcare ventilation systems.

Annual operating hours: 8,760 hours per year

Annual energy consumption of the existing system: 2.84 kW × 8,760 h = 24,852 kWh/year

Annual energy consumption of the EC fan system: 2.14 kW × 8,760 h = 18,746 kWh/year

Annual energy savings: 6,105 kWh/year

The comparison of annual energy consumption before and after the EC fan retrofit is shown in Figure 5.

Figure 5. Annual energy consumption before and after the EC fan retrofit.

Assuming an electricity rate for non-residential users in Europe is approximately € 0.19 / kWh the estimated annual energy cost savings are approximately: € 1,160 per year

Results and Discussion

The retrofit demonstrated that replacing a belt-driven centrifugal fan with an EC fan array can significantly reduce electrical energy consumption while maintaining the required airflow and system pressure.

Although the original fan system already used a variable frequency drive, the EC fan array provided improved efficiency due to several factors. First, the direct-drive configuration eliminates mechanical losses associated with belt drives. Second, EC motors generally provide higher efficiency compared with conventional AC motors, particularly at partial load conditions.

Fan arrays can also improve airflow distribution within the fan section of the air handling unit. Multiple smaller fans often produce a more uniform airflow profile compared with a single large fan, which may reduce turbulence and improve system stability.

Another advantage of fan arrays is operational redundancy. In systems with multiple fans operating in parallel, airflow can still be partially maintained if one fan becomes temporarily unavailable. This feature can improve overall system reliability.

Maintenance requirements are also reduced. Belt-driven fans require regular inspection and replacement of belts and pulleys. Direct-drive EC fans eliminate these components, reducing maintenance requirements and helping maintain consistent performance.

Although the total energy savings in this case are moderate due to the relatively small fan size, the percentage reduction in power consumption is significant. In larger ventilation systems with higher fan power, similar retrofits could result in substantially greater energy savings.

Conclusions

This case study demonstrated the energy performance benefits of replacing a conventional belt-driven centrifugal fan with an EC fan array in an existing air handling unit.

Measured test and balance data were used to establish the baseline operating conditions and evaluate the impact of the retrofit.

The retrofit maintained the required airflow of 7,828 m³/h at a system pressure of 585 Pa while reducing electrical power consumption from 2.84 kW to 2.14 kW, representing an approximate 25% reduction in fan energy use.

Under continuous operation, the retrofit resulted in estimated annual energy savings of 6,105 kWh, corresponding to approximately € 1,160 in annual electricity cost savings.

In addition to energy savings, the EC fan array provides operational advantages including improved controllability, simplified mechanical design, reduced maintenance requirements, and improved system reliability.

EC fan retrofits therefore represent an effective strategy for improving the energy efficiency of existing ventilation systems in healthcare and other commercial buildings.