Not all PPV fans are designed the same, perform the same, or even have the same airflow type. So understanding how your fan works and what its Performance Potential is will help you accomplish your goals- to Pressurize, to Ventilate, or both.
So here’s what you to know right off the bat: The very best PPV Performance you can have is from a huge fan with huge power because it offers a big airstream, big airstream momentum, and big entrainment to pressurize and ventilate. But, battery-operated PPV fans are built smaller for taking up less space on apparatus and for easy maneuverability. A small fan gives a small airstream which means the airstream needs to do a little magic for optimal performance.
We’ll be breaking up this article into the 3 primary systems in PPV Performance: System 1: The PPV Fan itself, System 2: The Airstream it generates, and System 3: The Structure. We’ll look at the variables of each system to understand how they influence the function and performance of the fan.
System #1: The Fan Itself
The two most important components of fan performance are its Airstream Size and Power. The way a PPV fan works is that it uses power to accelerate air into an airstream. Like we said before, the very best PPV Performance you can have is from a huge fan with huge power. Based on the Airstream Size and the amount of Power applied, a fan generates a certain level of Momentum in the airstream. So Airstream Size + Power = Airstream Momentum.
The amount of Momentum a fan can induce into the airstream defines the Performance Potential of that airstream. So the bigger the airstream and the more power you can put into it gives you higher Momentum and better performance.
For example, a small fan with a small airstream and small power will provide low performance because it is limited in the amount of Momentum it can induce into the airstream. A large fan with a large airstream and big power will provide high performance because it can induce high Momentum into the airstream.
Now don’t get us wrong, most PPV fans out there on the market today are either large but with small power, small fans with small power, or even small with big power, but all are limited in performance! PPV Fans are firefighting tools, and BlowHard believes they should be designed and optimized for that purpose. But for this blog, we’re focusing fan Performance Potential within ANY airstream.
So how do we measure a fan’s airstream potential, its ability to do the work? Well, a direct measurement of the Momentum in the airstream is called Thrust. Thrust, not CFM, is the most accurate method of measurement to determine the performance potential of any fan! You’ve heard the saying “every action has an equal and opposite reaction.” Well, Thrust gives a precise measurement of the airstream momentum because IT IS the equal and opposite reaction to the Momentum the fan has induced into the airstream. Thrust measures Momentum and it’s Thrust that measures your fan’s performance!
So to recap System #1 The Fan itself: it’s is the first component in PPV performance and it creates Momentum in the airstream in response to the fan’s Airstream Size and its Power. There is a Thrust reaction against the fan in direct response to the Momentum induced into the airstream.
System #2: The Airstream
Now historically CFM or volumetric airflow measured in cubic feet per minute, has been used to gauge a fan’s performance. CFM is a key component of performance, but it isn’t everything! You’ve got to factor in the velocity or speed to truly define a fan’s performance. You see, Airstream Velocity is actually Airstream Pressure. This combination of CFM and Pressure together are the building blocks of Momentum and Thrust. These are the true performance metrics of an airstream. So let’s dig in…
We talked about how battery-operated PPV fans should be small in size to reduce storage requirements on apparatus as well as provide easy portability for reaching more places quickly. However, because of their small size, the airstream is also small and is in a compressed, high-pressure state. But that small, compressed state is not an effective, usable form when high-flow is needed for ventilation. In order to get it into a usable high-flow form, the airstream has to be able to convert into a High-Flow / High CFM state (the magic we talked about earlier). It’s got a job to do and if it can’t do it, it won’t perform optimally because the state of the airstream will define how airflow works within the structure. Let’s break this all down…
So what is the job that the airstream has to do? It’s got to increase in CFM by Entraining air! Which means that as it travels, it pulls air into it from the surrounding environment and as a result, gets larger. So, the airstream actually changes state as it travels. The 1st state is right where it exits the fan and the 2nd one is anywhere downstream after it’s grown.
Now remember in System #1, the fan itself, it created Momentum from its Airstream Size and Power. For System #2, after it has left the fan, it’s the combination of CFM and Pressure that makes up the Airstream Momentum. So you can’t gauge a fan’s performance simply on a CFM number because you can have a fan that has high CFM and very little Pressure-it can’t do the work. You’ve got to factor in both CFM and Pressure to know its Momentum– the fan’s true performance, and we can directly measure Momentum by its opposite reaction which is Thrust.
Momentum and Thrust are the heart and soul of PPV Performance! Fans which generate high Momentum airstreams will be capable of Entraining more air to generate higher CFM, and more importantly, will maintain higher pressure when expanded!
Let’s look at those two Airstream Momentum States. State #1 is right when it exits the fan. At this point, it hasn’t entrained or pulled any air in yet. It is tightly condensed, tightly compressed, and has High Pressure. So, Airstream Momentum State #1 = High Pressure, Low CFM.
Airstream Momentium Sate #2 is anywhere down the airstream. Now it’s traveling, Entraining air and growing bigger. This state = Lower Pressure, High CFM. Remember we said that the airflow has to convert to a High-Flow state to get to high-CFM? We’ll it’s the effective and efficient Entrainment that will get it to transition.
What’s important to note is that an airstream with high Momentum (CFM and Pressure) will maintain that increased Pressure when it gets to the expanded state, which now means it has increased potential to DO THE WORK. A second point to note is that different fan designs will produce airstreams with higher or lower rates of entrainment. Some fans will have limited air entrainment like a straight jet because they haven’t expanded by the time they get to the door. Some utilize modes of entrainment, like the cone which have over expanded, resulting in reduced pressure in the airstream. Be sure to watch our short video on the BlowHard High-Flow expansion Jetstream.
So to recap System #2 The Airstream: the 2 primary factors of airstream performance are Momentum, and Entrainment. Momentum is the driving force within the airstream and Entrainment allows it to transition into different CFM & Pressure states.
System #3: The Structure
Every structure and situation are different. Doors are different sizes, buildings are different sizes, and so the pressure and CFM requirements are also going to be different. In order to generate the best outcome and maximize fan performance relative to the structure, it is important to understand those situations and to have both the proper fan and proper fan placement. Are you needing to pressurize, ventilate, or both?
A large part of performance is a fan’s ability to seal the air into the structure with its airstream. This is accomplished by expanding the airstream to match the size of the door as much as possible to limit the amount of air that can escape.
When using a fan to pressurize or ventilate a structure, you have to take into account both the structure inlet and outlet openings and choose the correct airstream state that we discussed.
- Momentum State #1: Condensed (High Pressure, low CFM) is used with the fan closer to the door when high pressure is needed. To increase pressure in the structure, outlet openings would need to be limited. In this case you would also need an air curtain to contain the pressure in the structure. An example of a high-pressure scenario is when needing to overpressure a region of a building to prevent smoke from entering and to provide an escape route for victims.
- Momentum state #2 Expanded (High Flow/CFM, Low Pressure) is most commonly used, and works best with the fan being set back from the door to entrain air and generate high volumetric flow/high CFM. To increase flow in the structure, outlet openings need to be increased. Examples of scenarios requiring High Flow/CFM are clearing smoke for visibility and providing fresh air, and to cool down a structure.
- Some circumstances will require both Pressurizing and High Flow. These cases would require a large fan with high power for extreme performance. A scenario requiring both High Pressure and High Flow/CFM are clearing smoke for visibility in larger and taller structures with restricted exit points, and for PPA attack.
To recap all of this information: fans with large airstreams and high power will produce high Momentum in the airstream. Airstreams can utilize either their High-Pressure state or leverage the Entrainment process to expand into a High-Volumetric Flow/CFM state. Your PPV ventilation performance will be highly influenced by your fan size, its power, its entrainment ability, how you set up your fan, and the configuration of the structure.
That was a lot of information but still just skimmed the surface of PPV fan performance. To see this information in video form with visuals, check out our YouTube channel: www.youtube.com/@BlowHardFans. Please reach out if you have any questions or want more information or clarification. info@blowhardfans.com
As always, take care and stay safe!
