Positive pressure ventilation (PPV) has become a very common practice in the fire industry, and as the benefits from it continue to become more documented and validated, its practice continues to grow worldwide. Evidence of this is seen in the number of different PPV fans now on the market, as well as emerging technologies in play.
One big game-changer is the entrance of dual-powered fans entering the market. These fans can be run on battery or a/c, tend to be more portable and compact, and use a cylindrical “jet” stream more suitable for the most commonly entranceway used in PPV, windows and typical man doors. Advancements in stream technologies have impacted the industry and have added to the complexity of PPV fan selection. All of this information can make trying to figure out what to look for in a PPV fan daunting. Hopefully this article will help shed some light on the subject.
When PPV was introduced to the industry, fans didn’t vary much, and they all used cone technology. With proper placement, each fan functioned in a similar manner, and volumetric airflow became an easy and valid way to gauge performance. A PPV specific group established at AMCA to recognize this. This group leveraged AMCA as a third-party industry tester to create a standardized test to rate the volumetric airflow of PPV fans. This was simple, unbiased, and great for the industry. Volumetric airflow, often stated as “CFM” or “m3/h”, remains a common value looked at to determine the performance of a PPV fan.
In recent years things have evolved and the industry has shifted. Jet technology was introduced, and has consistently outperformed cone technology at smaller, more commonly used pressure differential points, such as human doors and windows. Jet technology utilizes a concentrated high-pressure jet stream and this complete stream of air is dedicated to ventilation. A cone, with its rapidly expanded working area, significantly reduces working pressure at these common pressure differential points, and wastes significant air volume impacting the wall around the door. Suddenly, a 10,000 CFM AMCA rated fan using jet technology was outperforming 13,000 – 14,000 CFM AMCA rated fans using the cone technology. With man doors being the primary ventilation point, the recognized performance of Jet Technology has resulted in the industry shift to Jet Technology. It is important to note that AMCA is a useful tool for comparing similar fan technologies, but should not be used to as a comparison for different technologies. Because of these discrepancies, fan comparisons have been difficult for both the buyer and fan manufacturer.
Today’s marketing seems to be each company touting product capabilities, accurate or not, followed by the one-dimensional solution poised to sell it. In reality, fan effectiveness is not one-dimensional, but instead is a combination of things extending beyond the all-important fan performance, to how it interacts with and hopefully improves the overall performance of the firefighter. A firefighter’s workplace is often a state of emergency with intense conditions presenting challenges of an extreme nature physically and mentally, and at times life-threatening. The performance of a PPV fan (or any tool for that matter), should be evaluated from when the firefighter arrives on scene to when the firefighter departs. While fan performance is a critical metric, it is not the only metric. Fan performance extends beyond simply turning fan A on to compare with fan B, already set up in a controlled environment in ideal conditions. Instead, fans arrive with the firefighter to a high-stress emergency situation. The firefighter must retrieve the fan(s) from the compartment on the truck. The firefighter must transport the fan to the desired ventilation entrance, or pressure differential point, often times while carrying a host of other necessary tools or breathing apparatus. This may require walking some distance, overcoming obstacles, going up and/or down stairs, through door ways, through hallways or alleys. I’ve seen a PPV fan carried up a ladder and deployed into a window from a rooftop. The firefighter must then set up the fan at the desired or required distance and angle needed to maximize ventilation efforts, then the fan must be started/turned on. The more quickly this all happens, the more quickly the firefighter can begin other required functions, making “response time” not only important, but critical. Given the extreme stresses in play, it is equally important that the firefighter has the confidence and freedom to know the running fan will ventilate the structure without additional efforts of issues and in a timely manner and allow them to focus on other needed tasks. Finally, when the situation is under control, and often times the firefighters are mentally and physically exhausted, the fan must be transported back to the truck and placed back in the compartment without excessive exertion, strain, or injury. This is complete fan effectiveness.
Compactness is a fan effectiveness variable noted above. Space on a fire truck is a commodity, so a little goes a long way. The less room a fan requires, the better. This would include the size of the fan, as well as any external charging requirements the fan might have if hot-swappable batteries are used instead of fans containing high capacity integrated batteries.
Weight, shape, size, balance, and carrying options all play into transporting the fan. A light-weight, well balanced fan with handles designed to reduce stress while carrying make transporting the fan easier while reducing risk of injury.
Setup and adjustment should be fast, simple, and precise. In high stress emergency situations, firefighters are required to maximize efforts while reducing the time needed to do so. Placement and set-up of a PPV fan should be simple and require as little time as possible. Fans with flexible setback ranges allow for quick placement that takes little to no thought or measurements. Fans with brake systems that are easily accessible, release and set quickly, and have angle adjustments that can be accurately fine-tuned provide maximum entrainment value for rapid ventilation but require little time from the firefighter. In limited time emergency situations, this extra time saved could be the difference between life and death.
When using a PPV fan on battery, it may be necessary to ventilate beyond the capacity of the battery. These situations require the PPV fan be capable of running on a/c as well. Technology used to switch between battery and a/c is therefore important. Evaluation on whether or not it is automatic, or if ventilation is interrupted at any point, or if additional action must be taken is important. Fans that can switch from battery to a/c (and back) seamlessly and automatically without affecting ventilation is a benefit and becomes less the firefighter has to think or worry about. Taking it a step further, some fans have incorporated a blink-sequence for the LED path lighting that occurs when the fan battery has discharged the fan is no longer running. In a noisy environment where the fan cannot be heard running, it alerts the firefighter that action must be taken for continued ventilation. This allows for quick corrective action and reduces unneeded setbacks.
Thus far, the discussion has been on a variety of things to look for that can provide added value, the summation of which can make a big difference. But at the end of the day, the fan’s sole purpose for being there in the first place is providing ventilation. And firefighters have strived to understand what ventilation performance fans have, both from a budgetary and process perspective. So, let’s discuss fan effectiveness strictly from a ventilation perspective now.
Volumetric airflow is important when looking at ventilation because this is what feeds the air flow. Positive pressure ventilation (PPV) introduces pressure into this process to accelerate ventilation. To conduct positive pressure ventilation, you must select a specific point to generate working pressure in the structure. This requires a pressure differential point. This is the point where atmospheric pressure ends and systemic pressure begins. To generate working pressure, you must have a point where the fan can generate pressure without air escaping. The better you are able to generate working pressure, the more control you will have in controlling air flow through the structure. To better understand this, lets explore a few scenarios:
- Example 1: Setting a fan up to blow across a warehouse structure in “open air” will not create pressure for controlled air movement. Open air movement simply creates air circulation. The air will circulate because there is no point where pressure generation or pressure differential can occur. You do not have a pressure differential point, you will not create pressure and work cannot be accomplished. Note: Open air circulation has a place and can be useful in many industries but is not helpful in conducting positive pressure ventilation
- Example 2: Setting a fan up on a door opening which is excessively large, say 10X relative to the air stream will not “seal” the door. If the door is excessively large the air will easily escape from the edges of the door and you will not generate working pressure. This cannot work as a pressure differential point, you will not create pressure and work cannot be accomplished.
- Example 3: Setting up a fan on a door opening in which the stream of the fan covers more than 50% of the door area. The perimeters of the jet stream will entrain air to create pressure in the structure. The structure will have a differential pressure with which work can be done, flow paths can be created.
– The fan can be placed outside the structure blowing in to create positive pressure or inside the structure blowing out to create negative pressure.
It is important to note: You are not building pressure by closing all openings on the structure. A fan must be capable of generating a sufficient volume of air to build pressure with the desired flow paths open. Volumetric airflow and pressure must work together for true fan effectiveness with regard to ventilation performance.
Fan performance is a key metric for any battery-operated fan. Battery operated fans have taken the approach of “jet” technology as it is able to build good pressure in the structure. Jet technology is a good option as it works well for man doors and windows. The size of the jet has a dramatic impact on the fan performance and battery life. Large area jets are intrinsically more efficient as the fan does not need to work as hard to create a high flow air stream and the jet stream is larger which results in higher volume entrainment with less power. Large jets enhance fan performance and/or extend battery operation time at a given level of performance. It would not be uncommon for a larger area PPV fan to outperform a smaller area PPV fan that has a higher measured CFM. It is important to balance the volumetric airflow with the maximized Jetstream area. This balance is a large contributor to fan effectiveness and should be considered. Recent tests done with fans using a similar jet technology have confirmed this when a 20-inch fan at 700W had a similar performance as an 18-inch fan at nearly 1000W and a higher claimed AMCA rated CFM.
With the latest fan and battery technology, battery operated PPV fans have outperformed petrol-driven fans in the field. The combination of ease, performance and space saving designs you can expect to see in industry shift toward battery operated PPV fans in the near future.
In recent years there has been a growing trend to selecting and using fans with jet technology. Does that mean the old cone technology is going away? The answer is….it shouldn’t. Each technology has its place. Cone is better for large openings, Jet is better for small openings. There are two key components, pressure and entrainment area.
The point where air is driven into the structure is the point where pressure is generated. It is important to consider the opening where the air is driven into the structure, the point of pressure/pressure differential point.
The basic concept is that the size of the stream should be proportional to the size of the entrance point while maximizing pressure in the stream. For a jet, the opening size should be 1.5X-2.5X jet stream for entrainment, larger openings will work but blowback will be increased. For a cone, the shape of the cone should directly match the entrance point. Cone shapes will work better on a large opening such as a garage door or roll-up door. A jet shape will work better on smaller openings such as man doors or windows. However, choosing a roll-up door/cone over a man door is not as productive because the pressure of the cone is still limited. A high volume jet on a proportionally sized entrance will provide high pressure and volume, providing higher flow control and more effective ventilation. That said, if the fire department calls primarily involve large structures with over 50% bay/roll-up doors, PPV fans using cone technology would be a good choice.
The most versatile fan would balance large working area with jet technology, utilizing a large diameter Jetstream. Selecting a fan with jet technology with a larger diameter shroud would take advantage of larger working area. Some companies have taken steps to develop technologies that focus on this very concept, expanding the working area beyond that of the shroud while maintaining a powerful Jetstream. This results in significantly larger entrainment and working areas while maintaining high pressures associated with jet technology. Fans using this technology inherently offer these benefits:
- Bigger jet
- Higher volumetric flow rates
- Higher entrainment
- Higher pressure
- Increased battery operating time
- Increase overall fan effectiveness
Portability and the ability to operate independent of additional power sources is key in the fire industry, as the environment and challenges for each call is unknown and unique. This makes petrol driven and battery driven fans very attractive. However, the safety concerns with petrol driven fans with elevated CO levels along with portability and storage requirements have highlighted the ease of deployment and minimal maintenance requirements with battery driven fans and have contributed to their uprise. Adding fuel to this fire, battery technology is everchanging. High power density batteries available today provide the avenue to the energy needed to operate a PPV fan. Li-Ion is most commonly used in today’s battery driven PPV fans and offers more energy transfer per volume. So, the question then becomes should you go with hot-swappable or High Capacity Integrated batteries?
Batteries are simple but at the same time a bit complicated. Let’s skim some basic battery concepts and explore choices.
As the power requirement of a battery increases, the battery performance decreases. Under continuous high stress the battery gets hotter and the life decreases. Performance and capacity will vary depending on the cell configuration.
- Batteries have a “C” rating. This is the amount of power a battery can discharge.
- Consider a battery pack which is 200 Watt-Hours.
- At 1C (Capacity X 1)
- The battery will deliver 200Wh X 1C = 200W
- The approximate battery run time will be 200Wh/200W = 1 Hour
- At 2C (Capacity X 2)
- The battery will deliver 200Wh X 2C = 400W batteries will see high stress/reduced life with continuous use
- The approximate battery run time will be 200Wh/400W = ½ Hour
- Consider a battery pack which is 1000 Watt-Hours.
- At .2C (Capacity X 1)
- The battery will deliver 1000Wh X .2C = 200W
- The approximate battery run time will be 1000Wh/200W = 5 Hours
- At 1C (Capacity X 1)
- The battery will deliver 1000Wh X 1C = 1000W
- The approximate battery run time will be 1000Wh/1000W = 1 Hour
- At 2C (Capacity X 2)
- The battery will deliver 1000Wh X 2C = 2000W batteries will see high stress/reduced life with continuous use.
- The approximate battery run time will be 1000Wh/2000W = ½ Hour
Hot swappable batteries are capable of providing extended run time by changing the batteries out but have limited power capability which limits performance. This can be detrimental when high performance is required. The extended runtime also requires the fan to be serviced and ventilation will be interrupted from this fan during this service. Finally, hot swappable batteries experience high stress even at limited performance. Let’s explore a scenario using hot swappable batteries.
- Consider 6 battery packs which are 200Wh each will provide a total capacity of 1200Wh.
- If 2 packs are used at a time the total capacity is 400Wh.
- A reasonable discharge rate to prevent overheating is 1.5C or 400Wh X 1.5C = 600W.
- Run Time
- Operating this configuration at 600W provides: 1200Wh/600W = 2-hours of run time.
- With a charge time of 4-hours it is not reasonable to assume a continuous use of batteries unless 10+ batteries are being swapped and recharged.
High Capacity Integrated (HCI) batteries are larger. This inherently means higher performance capabilities at the same “C” rating. This also means that a HCI battery with an equivalent “total” capacity can provide equal runtimes at the same power (2-hours @ 600W) with significantly reduced battery stress (extends battery life) and while providing continuous, non-interrupted ventilation. And if performance is required, fans using HCI batteries can produce significant power such that a properly designed fan can perform like a gasoline driven fan. This expands the usability for a HCI battery driven fan to scenarios not possible before, such as realistic ventilation of large warehouses and successful pressurization of high-rise stairwells. Let’s explore a scenario using High Capacity Integrated batteries.
- Consider 1 battery pack which is 1200Wh.
- A reasonable discharge rate to prevent overheating is 1.5C or 1200Wh X 1.5C = 1800W (3X Hot Swappable performance.)
- Run Time
- Operating this configuration at 600W provides: 1200Wh/600W = 2-hours of run time.
- Operating this configuration at 1800W provides: 1200Wh/1800W = 40-minutes of run time.
With batteries come charging needs, and there are differences in charging requirements between hot swappable batteries compared to HCI batteries that should be considered. Charging hot swappable batteries requires additional external chargers. This significantly increases the footprint of the storage and adds complexity to the wiring system. Limited performance will require longer runtimes to achieve similar ventilation, which may require an increased number of batteries and external chargers.
Fans using HCI batteries also use an integrated charger built into the fan, so charging simply requires the fan to be plugged in. This significantly reduces the footprint of the complete system on the truck. Some companies incorporate fast charging from 0 – 90% battery capacity. This means in 2 hours nearly all battery capacity is restored and available for use. A high capacity battery allows the fan to be charged and reused quickly with a partial state of charge in excess of lower capacity batteries at full charge, and can be done without damaging the battery.
Hot Swappable vs High Capacity Integrated Battery Summary:
- HCI batteries have extended runtime without additional setup/swapping.
- HCI batteries have higher performance.
- HCI batteries reduce battery stress/extend battery life at equivalent power.
- HCI batteries have a higher “fast charge” capacity for quick turnaround use.
- HCI batteries do not require additional truck space for charging.
- Combine fans using jet technology and expanded area with HCI batteries for continuous runtimes as high as 8-10 hours at an equivalent performance lower area lower volume jet fans.
- Hot Swappable batteries can be charged when the fan is running. When considering charge rates, 10+ batteries and a dedicated person is required for continuous swapping to ensure continuous fan operation with downtime during battery swapping.
Finally, as you define your performance needs, hands on testing to see how fans align with your needs is the best approach. Being able to pick it up, carry it, set it up, see how it fits in the truck compartment, etc., can shed light on what fans truly have the extra values. Side by side comparison performance tests are an important part of determining ventilation performance, and we recommend this be done by the fire departments as they evaluate fans. A structure resembling a structure size common for your area, with an entrance you would typically use (likely human door), and an exit point similar to what you would typically use that is not directly across from the entrance point that can be opened, like another human door or window, is best. Also needed is a low-pressure differential manometer and an anemometer to measure wind speed. Using the differential manometer, you can measure the difference in pressure between atmospheric and systemic pressures. Then using the anemometer, you can measure the wind speed at the exit point. You will see that as pressure increases, as does the wind speed at the exit point. This method is a great way to determine performance differences as well as validate/debunk manufacturer claims.
Trying to make your way through the decision process for what tools to purchase and use is often difficult and daunting for the average person. Add the high stress, physically and mentally draining conditions, often times with lives on the lines, when a firefighter reaches for a tool, it had better perform as advertised on all levels. In this article we outlined many things to consider when choosing which PPV fan you want in the hands of you and your team. And while all fire department may vary slightly in their strategies and needs, performance is one thing that tends to be common. We hope this helps you decide what performance you’re looking for, and what to look for in a fan in order to get the most value. And happy ventilating!
For more information, go to www.blowhardfans.com