Positive pressure ventilation (PPV) is a crucial and ever-evolving aspect of firefighting. Advances in this field include the development of battery-powered PPV fans. These cordless tools offer the advantage of increased portability, convenient power and clean exhaust. However, battery-powered PPV fans often lack the power of their gas-powered counterparts. High performance requires high power.
A fan uses power to generate energy in an airstream. In physics, this energy is called kinetic energy. The energy of an airstream is directly related to the power applied. Kinetic energy of an airstream is combination of air velocity and size (area). Fans with a small area must have higher velocity to create the same energy as large fans.
Effective ventilation requires the airstream to be converted into a usable state and size. Because fans must be portable, they are small. This also means that the airstream is small. This means that the air directly exiting a fan is in a high-velocity compressed energy state. This compressed energy state must be expanded into a usable form for the best performance.
In reality, structure openings (doors, window, etc.) are different sizes, and the fan’s airstream must optimally expand to fill the doorway for the best performance. We call this process of expansion entrainment. In the process of entrainment, the energy of the air stream transfers to a larger mass of air. As mass is added to the air, the air slows. Assuming the process is perfectly efficient, the energy of the airstream does not change during entrainment, it just takes another form in an expanded and slowed state. Entrainment is the process of changing the airstream from a compressed energy state from the shroud into an expanded usable energy state. This process of entrainment/expansion increases flow but reduces pressure.
Historically, two types of airstreams are used in firefighting: cone and jet. Each airstream type utilizes different types of entrainments. Cone airstreams are a result of turbulent mixing immediately when the airstream exits the shroud. Turbulent mixing results in very aggressive entrainment. While cones are a highly effective method of reshaping the small airstream into a large area, this results in low velocity and pressure. Turbulent mixing creates effective entrainment but the cone airstream is inefficient, causing significant loss in ventilation rate. Jet airstreams are typically small in size and maintain a very high velocity but typically exhibit less effective entrainment, which limits the expansion to fill the entrance. When set back a long distance, a jet airstream can transition into turbulent mixing for better entrainment but this is not realistic for use in the field. If sufficient entrainment is not achieved within the setback distance, the full energy of the airstream cannot be utilized.
A large-diameter jet airstream requires less entrainment to match the structure opening size, making it more efficient and more effective at driving airflow with less power. This allows firefighters to place the fan within a reasonable distance to the entrance while still achieving effective ventilation.
BlowHard not only studies the physics of fans, we leverage physics in our fans. This is why we design all of our own components. Through this process we are able to achieve maximum performance in ultra-compact designs.
BlowHard designs High-Capacity Integrated batteries to maximize power while reducing the footprint and effort needed to store and manage this power. The high power applied to the fan ensures high energy is being exerted into the airstream. BlowHard’s High Flow Jet technology produces a jet airstream that immediately expands beyond the fan exit point yet remains a jet airstream. This enables firefighters to experience the performance of a larger fan in a compact package. These fans take up significantly less space in the apparatus compartment, are lightweight and highly portable, yet perform like larger fans. Ultimately, this efficiency means the job gets done more quickly and effectively, which is the primary goal.
BlowHard believes in the advancement of battery-operated fans and the potential service they can provide to the industry and optimizes every aspect of the fan to ensure maximum performance.
About the Author
Benjamin Hadlock is Vice President of BlowHard.
For nearly 10 years Benjamin has been a driving force in BlowHard’s strategic journey in the research and quantification of fan performance as part of product development. These efforts by BlowHard have redefined the capabilities of PPV fans, specifically with regard to overall fan effectiveness while leveraging the convenience and power of the latest battery technology. Helping to lead the quest to be a true service to the fire industry, he has been instrumental in the release of the new fan series using High Flow Jet Technology from BlowHard.
