An HVAC (Heating, Ventilation, and Air Conditioning) System does more than just supply heating and cooling solutions to indoor areas. The HVAC is comprised of different systems that move air among the indoor and outdoor areas. Their purpose is to keep both commercial buildings and residential homes cool during summer’s sultry hot weather and warm during the frigid winter. Combined with the ventilation system that filters contaminants out of the indoor air and control humidity levels to keep the air your breath healthy and at optimal comfort levels.
To aid the exchange of inside and outside air, fans are essential elements in HVAC systems to establish the needed air flow. While all HVAC systems require fans, the physical composition and intended purpose of each type of fan vary.
The intention of this article is to describe each type of fan alone with the pros and cons. Keep in mind your local municipal codes when installing any HVAC units or fans. Three types of most common HVAC fans are – axial fan, forward-curved centrifugal fan, and backward-inclined fan.
Don’t let the simple design of the axial fan fool you. With propeller shaped blades arranged on a rotating shaft, they are designed to draw air from one side of the fan and then release it through the other side. This design can create a high volume of airflow, however, it works best with little air resistance.
Since the axial fan is not best suited for resistance airflow (high static pressure), they often work best and the least expensive option for outdoor AC (air conditioning) condensers, cooling towers, combustion engine and electronic component cooling to sustain needed airflow to release heat with little to no resistant airflow.
Compared to an axial fan, the centrifugal fan establishes a higher air pressure (assuming the same airflow) because of the hamster wheel or water wheel design.
Either belt or directly driven, the main purpose of a centrifugal fan within the air-handling unit (AHU) is to force air directly into the ductwork. Since the AHU combat the static pressure to blow air into the duct system, a centrifugal fan would far surpass an axial fan which is unable to fight the resistance resulting in poor airflow.
Considering that centrifugal fans produce more noise and are slightly more expensive to run than axial fans, it is only recommended to use them when the application requires it.
Backward Inclined Fans
Whether curved or straight, these unusual shaped fan blades may give the impression they are installed incorrectly. Often used in industrial settings, they can handle high air flow and variable resistance – in applications such as – such as dust collectors, process cooling and glass tempering and incineration systems.
Even though the axial fan may be less expensive to run, it may be ineffective on certain applications that centrifugal and backward-inclined fans would offer superior performance with an added cost. When installing a new HVAC system or replacing on older unit, especially in a commercial setting, for best results, obtaining a professional opinion of a HVAC design engineer is highly recommended.
Michael Tobias, PE, is the principal and founder of Chicago Engineers. He leads a team of over 30 mechanical, electrical, and fire protection engineers. Although Chicago Engineers main headquarters are in NYC and Chicago the business has led over 1,000 engineering projects in New York, New Jersey, Connecticut, Pennsylvania, Florida, Maryland, and California, as well as Malaysia and Singapore. Michael is an advocate for green technology and energy efficiency.