The Kitchen Air Inc Difference:
It starts with our slogan: Experts in Commercial Kitchen Ventilation. It is the only thing we do, which is why we are the best at it. When you work with our team, you have full access to experience in every area of the industry. We have been involved with servicing, manufacturing, research and development, installation, and startup. We are familiar with all of the major manufacturers and styles of hood systems developed over the last 50 years. Our hands-on experience and knowledge of what works and what doesn’t is where we bring value. It takes field experience and engineering training in order to design successful systems: We have both. We know how to calculate proper airflow rates, duct sizes, and we know how kitchen ventilation systems interact with the rest of the HVAC system in the building. You want your kitchen ventilation system designer to be someone that can proficiently communicate and work well with your hood system installer, electrician, fire system contractor, engineer and even code official if necessary. We readily interact with all of these types of professionals in order to achieve success in designing the most appropriate system for the end user.
4 Main Kitchen Air Inc Principles of Design:
- Safe and Code Compliant
- Performs Adequately and Efficiently
- Easy to Repair and Service
We take a very personal approach in designing every kitchen ventilation system to specifically meet the needs of its operator. There is a reason why we do not simply sell cookie-cutter type hood packages on this website: Every system is different and requires the attention of a knowledgeable expert.
Call us and get started designing your system Today! 1-800-524-7352. We look forward to working with you on your project. We provide quick turn around on pricing and offer job specific drawings for you to submit to your MEP engineer. Our systems are manufactured at one of six production facilities strategically located around the country in order to provide the lowest shipping costs and shortest lead times in the industry. Finally, we will support you along the entire way up until the system is fully installed in order to ensure top system performance. We have a strong network of installers/contractors that we work with in your area that can provide onsite support if needed. We work with all types of customers, whether it is an engineer, architect, GC or the restaurant owner direct.
Below are the steps involved in our design process. We will work with you through our design process and ensure your system matches your specific needs and adheres to our core design principles: Safety, Performance, Serviceability, and Affordability.
Our General Process for Design (Note: All systems are unique, this is a general overview):
- Identify the cooking appliances that are going to be covered by the hood.
- Identify the style of cooking that is going to be performed.
- Identify the Ceiling height, walls, wall construction type, and any other physical restrictions that would limit the style of hood that is available to be used.
- Determine whether a Type-1 hood is required (grease application), or a Type-2 (non-grease application).
- Select an appropriate style of Listed Hood based on the information from steps 1 and 2. (We cannot stress enough, the importance of making sure a Listed hood is installed.) Be sure to account for clearance to combustibles. The 5 basic types are listed below and are described in the design guide.
- Standard Wall Mounted Canopy
- Island Canopy
- Low Proximity/Back shelf
- Pass Over
- Determine the appropriate overall length, depth, and if applicable the height of the hood based on the size of the cooking appliances and the style of cooking. If you have an appliance layout drawn to scale, the length can be measured off of the drawing. If all that is available is specifications on the cooking appliances, reference the cut sheets to determine exact sizes. For the length of the hood (left to right if standing in front), there must be 6” over-hang on both sides. Be sure to account for space in between the cooking appliances (a general rule of thumb is to add an inch between each appliance. It is better to be conservative and be a little oversized than undersized.) In regards to the depth of the hood, you must reference the front overhang requirements for the specific model of the hood based on its listing. Finally, select the height of the hood based on the ceiling height and style of cooking (Example: High smoke applications from a char-broiler may require a 30” tall hood rather than a 24”).
- Select what kind of grease filters are to be used. We only recommend the use of Stainless Steel filters. For low grease applications we use Standard Baffle. For high grease applications or with systems with Pollution Control Units, we recommend that Captrate Solo Filters be used. For solid fuel applications, spark arrester rated style filter must be used.
- Calculate the required exhaust airflow rate in CFM (Cubic Feet per Minute). Every listed hood has a minimum design CFM per linear foot based on the temperature rating of the appliance it is covering. If there are multiple types of appliances, determine which is the worst case scenario and use that to reference the CFM/Ft to calculate total exhaust airflow.
- Calculate the amount of dedicated Make-up Air (MUA) required by the system. Most of the time this is 80% of the total exhaust. For smaller square footage restaurants, 90% may be required to sustain adequate building pressure due to limited transfer air available from the HVAC System. There are also instances when less than 80% MUA is specified when the cooking space is required to be absolutely negative relative to other areas in the building (EX: Airports). Finally, sometimes MUA is not required at all (EX: Outside Concession Stations).
- Determine how the MUA is being distributed. Most of the time this will be done with use of a Perforated Supply Plenum (PSP). If this is not possible, we recommend using perforated diffusers or another means depending on the space that introduces air in a non-disruptive manner to hood smoke capture performance. Note: We never recommend distributing airflow inside the capture area of the hood, or the method of front-face discharge through grills. These designs result in the extremely poor smoke capture, are difficult to balance, and interfere with the efficiency of the HVAC system and comfort level of the space.
- Determine the minimum size of the ductwork and how the ductwork is being ran to the outside of the building for both the exhaust and supply air. Our target velocity is between 1500 and 1800 FPM for exhaust airflow and 1200 FPM for MUA airflow depending on space conditions. To calculate the required minimal cross-sectional area of the ductwork use the formula: A=Q/V, where Q is your Volumetric flow Rate (Total Exhaust airflow rate in CFM calculated in Step #8), and V is your target Velocity (1500 to 1800 FPM). For Instance: The required Area of the grease exhaust ductwork required to sustain a target velocity of 1500 FPM for a hood designed at 2000 CFM Exhaust would be:A=Q/V = 2000 CFM/1500 FPM = 1.33 FT^2 This equates to a 12×16” duct.More on ductwork sizing is included in its own section below. It is critical that the ductwork is specified at the time of design for optimal system performance and accurate fan sizing.
- Determine the Static Pressure associated with both the Exhaust and MUA Ductwork.
- Find out what Phase and voltage will be provided for the Exhaust and Make-up Air unit.
- Determine what fans are required based on their location, airflow, static pressure, and for MAU if a heating/cooling is required .
- Size the electrical controls package based on Phase, voltage, HP of motors and whether or not an energy management system will be used or not. Determine where the fan/light switches will be mounted based on input from the end-user if possible.
- Find out if an end Cabinet panel is desired for the fire system to be housed and add if necessary. We take the stance that fire systems are always a buy-out item, piped in the field. We find that this simplifies the design, purchasing and installation process when it is solely the responsibility of the Fire System Contractor onsite. This saves the end-user money by not marking this portion of the system up and if there are any un-foreseen changes in the appliance lineup, the pre-piping does not have to be redone.
- Determine if there are any further accessories that need to be provided with the hood system. (EX: Hood Wrapper, Wrapper Channel, Backsplash, wall panels, end-panels, etc)
- Generate an AutoCAD drawing detailing all system specifications and submit to the engineer/architect/owner for their review. Autocad Sample Drawing
- Provide proposal for equipment to purchaser and modify design if necessary if maintaining budget is an issue.
- At the end of the design, be sure to review all annual servicing costs associated with maintaining the system, and that proper access is available to both clean and service the equipment (Proper access panels, service platforms, etc.) If a system can’t be accessed properly for service, it will break down. Usually Friday night at 6pm.
Further Information on Key Areas of Design:
It doesn’t matter if you have the most expensive, high-end, hood in the world; If the ductwork is not adequate, the hood is not going to function properly. Here is a word to the wise: If your duct installer can’t tell you the velocity through the ductwork at the time of bidding the job, get a new installer.
One of the hardest problems to fix regarding under-performing kitchen ventilation systems is when you are limited by how much you can increase the volume of airflow due to limitations in duct size. This is common on both the exhaust and supply side. Whether it was due to poor design calculations on paper, limitations on space in the ceiling, or flat out the installer cutting corners, the ultimate solution is usually so costly to fully implement, it rarely gets resolved. As a technician, I would take a lower quality hood and fan with adequate ductwork rather than a high end hood and fan with poorly undersized ductwork any day of the week.
This presents a good opportunity to talk about how much air you can truly put through a given cross-sectional area of duct. Whenever we run into the scenario of a system being under design in the field, “maxing out the system” is the first step to find out how bad the situation really is. Over the past decade, we have found that with standard up-blast exhaust fans that can roughly generate 2” of static pressure, the maximum achievable velocity through the ductwork in a field environment is about 2100 FPM*. It means that every given duct size has a rough number as to the maximum amount of airflow you can expect to achieve in the field.
*Note: These is the consistent number that we have found in the field with longer duct runs, with turns in direction and system effect. Under conditions of absolutely no system effect in our test lab with straight up, smooth round duct, higher velocities were observed in the range of 3500-4000 FPM.
From the volumetric flowrate Equation Q = V x A, you can estimate about how much airflow you can expect to max out at in the field if you know the smallest choke-point on the duct run. For instance: If you have a duct run with its smallest sectional area being 10×22”, its area in Square feet is 1.53 ft^2.
Thus, Qmax = Vmax x A = (2100 FPM) x (1.53 FT^2) = 3213 CFM
If you were already measuring airflow close to that, you would know that the ductwork would need to be increased in size. In this case recommending to replace the exhaust fan with a larger unit or upgrading to a larger motor may not help at all and would be a waste of the owners money.
Besides the physical size of the ductwork, the other factor that can cause major problems with airflow is referred to as system effect. This is the reason why in the previous paragraph we found that the maximum achievable ductwork velocity in a typical system in the field was much lower compared to what we found in perfect laboratory conditions. There has been much written about this topic going back to the mid 1970’s. Below is the definition and a link to an article that does a good job explaining it. The YouTube video further down put out by Cook (fan manufacturer) is a great visual display of how detrimental System effect can be on the performance capability of a fan.
Definition: System effect is the generation of higher than expected pressure drops through changes in duct direction or geometry
The two main take-aways pertaining to System Effect are that it is completely undesirable and it cannot be measured. As a designer or an installer, you want to minimize System Effect as much as possible. Some examples of what can cause major system effect and in turn poor KVS performance are listed in the “Things to Avoid” section of this website.
The problem of how to properly replace the exhaust airflow taken out of a commercial kitchen is one that has existed for decades. The absolute best method in solving this problem remains a topic of great discussion among engineers, manufacturers, chefs and restaurant owners. Depending on who you ask, you will get a multitude of answers ranging from high tech, high-cost solutions to simply a screen door in the back of the restaurant. There is one undeniable truth however: The Make-up Air is going to come from somewhere. Its simple physics. What goes out, must come in.
As a restaurant owner it’s sometimes easy to only care about up-front capital costs, only focusing on exhaust airflow and how to get the smoke and heat out of the kitchen.
As a design engineer, all of the airflow numbers have to add up on paper, so you are forced with having to incorporate a solution that can’t be fudged.
So what is the best solution? It depends on the situation.
Let’s start with the size of the kitchen. More importantly, the size of the kitchen verses the size of the dining room/customers area. The smaller the ratio is between the size of the kitchen and the size of the entire building, the less the effects of not accounting for makeup air will be felt. For example, if you are designing a single 4 foot hood for a small cooking application in a 100,000 square foot consumer shopping space, it probably wouldn’t make sense to invest in a dedicated make-up air system since the low percentage of required makeup air will be accounted for through the economizers of the rooftop units of the HVAC system. On the other hand, if you are planning to operate a 20 foot hood in a small takeout restaurant with only 500 square feet of consumer space, the importance on having dedicated make-up air will be extremely magnified. These two examples are sort of the extremes in either direction on the spectrum.
A more common example that applies to the more conventional restaurant would involve a 12 foot hood in a restaurant that has 100 seats. In this example, the need for Makeup air is definitely present. 80% of the exhaust airflow would be the amount that would be considered “dedicated”, being provided from a 100% outside air unit. The remaining 20% of the exhaust airflow is “transfer” air and would come from across room, but ultimately coming into the building through the fresh air intakes of the HVAC system.
There are numerous ways dedicated make-up air is introduced in/around the hood system in today’s restaurants.
- Internal Compensating (Short Circuit):
The first of these methods (Internal Compensating/Short Circuit) is the absolute worst way to introduce make-up air and is actually illegal in the State of Minnesota. This is for good reason, as this method involves the distribution of the makeup air directly inside of the hoods capture area. In doing so, this creates immense turbulence inside of the hoods capture area and interferes with smoke capture. This is the worst kind of hood system to encounter in the field. It is impossible to achieve 100% balance and smoke capture and containment by distributing makeup air this way. This method of distributing makeup air should never be used.
- Front Face Discharge:
This method involves discharging the makeup air through a series of registers or less commonly perforated grills on the front face of the hood. This is one of the cheapest ways to distribute makeup air which is why is extremely common among low-end manufacturers and sheet metal shops. Proper balance is difficult to achieve because the amount of area available for the MUA to travel through is extremely small relative to that on the exhaust side. If the airflow is actually set to design, the result velocity at the discharge of these registers is astronomical. This forces the airflow across the room where it interferes with the HVAC air, plated food, or worst case scenario the customers in display cooking applications. This method of distributing makeup air should never be used.
- Back Return:
To be completed later.
- Perforated Supply Plenum:
To be completed later.
Make the PSP with 2 layers of perforated metal, not one.
More in this section later.
Energy Management Systems:
Energy Management Systems have come a long way in the industry over the past 15-20 years. Evolving over time from the original 2 speed fan systems with manual wall switches, all the way to fully modulating digitally controlled systems utilizing variable frequency drives. All energy management systems in the industry currently operate off of monitored cooking temperatures, some even go further and will increase/decrease exhaust airflow based on the detection of smoke in the capture area of the hood.
The main principle that allows so much energy to be saved by utilizing demand control ventilation techniques is the 3rd Fan Law, which states that there is a cubic relationship between the change in fan speed and its required power usage. For instance, a 20% reduction in fan speed on a modulating system will result in an actual required fan power output reduction of 48.8%. This can result in some major energy savings if everything is functioning as designed.
The decision to invest or not in a Demand Controlled Ventilation system as a restaurant owner can be a tough one, especially when faced with budgetary constraints and if it is an unproven restaurant concept. As a service company, we have worked on a multitude of the different styles and manufacturers of energy management systems in field over the past decade. We have seen systems that have been extremely successful, and have seen others resulting in frustrations among business owners. The general trend in the industry is that these types of systems are getting more and more reliable and affordable each year with increased advancement of technology. If as a restaurant owner you can afford the initial capital investment and your style of cooking operations justifies using one, then installing a Demand Control Ventilation (DCV) system should be seen as an opportunity to save energy and money. With that said, there can be unforeseen disadvantages to using these types of systems and even conditions that they should never be used at all that as an owner or designer should know about when making an educated decision on whether or not to include one on your next kitchen ventilation system.
Pros to Energy Management Systems:
- Energy Savings and reduction in cost of utilities from savings on both Kitchen Ventilation System side and HVAC side.
- Short Pay-back period if operating as designed.
- Variable Frequency Drives are soft start which prolongs belt life.
- May result in Tax Rebates from government
Cons to Energy Management Systems:
- Initial Investment cost is higher than a traditional single speed system.
- Are more difficult and expensive to repair compared to traditional electrical control packages of single speed systems due to complexity of system and availability of specialized parts.
- Variable Frequency Drives are more susceptible to damage resulting from electrical power surges. (Note: This is getting better with use of line and load reactors in industry.)
- Limitations on load side wire runs due to use of VFD’s. (How far away the fans can be installed from control panel.)
- Compatibility issues can occur if the fans are not provided by the same manufacturer as the energy management system (Especially on the Make-up Air Unit side when a heater is involved).
- If three phase power is not available in the building and single phase power is used on the input “Line” side of the VFD’s and there is a problem, the system cannot simply be bypassed, by running the 3 phase motor directly off of the breaker. This would only be a problem in an emergency situation and only for systems of this nature (Single Phase Input).
- Calibrating these modulating systems can be complicated and is often overlooked at time of startup due to the fact that “Actual” cooking operations must be in effect in order to properly dial in the system. It is rare that a second trip is made after restaurant is fully operational or that a system is truly operating 100% efficiently to design in the real world restaurant environment. Worst case scenario of this is when a system is stuck in either low speed all the time, or high speed all the time, resulting in no modulation and either lack of smoke and heat capture at the hood or no energy savings at all.
Overall Summary of Energy Management Systems:
The use of an Energy Management System is economical when installed, designed and maintained properly. Many of the “Cons” in the above section fall under this category and are not related to the system itself, however they should be included because these conditions surface in the field on a regular basis. There are only 3 cases in which we do not recommend using energy management systems. 1) On cooking operations that never modulate. If you are cooking on high output temperature/smoke operations all day long, it makes absolutely zero sense to install a modulating system as it will be in full speed all the time. 2) In areas/buildings that are prone to poor electrical service. If you experience a lot of power surges and dirty voltage, the VFD’s in your system will be prone to burning up, resulting in expensive repairs and restaurant downtime. 3) Cases in which the Fans are located further away than the manufacturers recommended maximum distance from the energy management system control panel.
To Summarize, If you can afford an Energy Management System and you have the correct type of cooking process and consistent/clean voltage to your restaurant, then get one; but much like an expensive car, you shouldn’t complain when it is more expensive to fix.
Hood Grease Filtration:
It is best to capture grease as close to the source as possible. This means at the hood, right above the cooking appliances. In doing so, you mitigate as much risk as possible from having a fire in your system, reduce the cleaning load in your ductwork, and protect your fan and roof from excessive grease build-up. There are many types of grease filters available in the market today. Not all filters are created equally. It is important to understand the difference when choosing a filter that works for your system. Depending on the cooking application, the cheapest option may not provide enough performance, whereas the most expensive option may be too efficient for your needs and thus overkill.
When selecting a filter, the number one most important factor is that it is safe. This means compliant to current NFPA 96/IMC standards and UL 1046 listed. In short, this ensures that the grease filter has been tested by a third party and demonstrates its capability to prevent flames from passing through into the ductwork in the event of a fire. It also verifies the filters ability to drain captured grease safely in a manner such that it does not fall back on the cooking surface. It should be noted that these testing standards do not relate to grease particle extraction efficiency.
Hood Filter Evaluating Criteria:
Material Type: Stainless Steel, Galvanized, Aluminum, Specialty (spark arrester, etc).
Grease Extraction Efficiency: The percentage of grease extracted by the filter at a specified micron level.
Resistance To Airflow: The static pressure drop across the filter at a given flowrate. For the most part, the higher level of efficiency, the higher level of resistance to airflow, thus the more power that the fan needs to output in order to sustain the required level of airflow.
Durability: How long will they last under vigorous restaurant environment conditions.
Affordability: How much of an upfront investment.
Cleanability: How hard is it to clean the filter. In general, the more efficient the filter is, the harder it is to clean.
Noise: How loud are the filters at the required hood airflow rate.
Ergonomics: How easy are they to handle. Weight, sharp edges. Etc.
As a company, we take the following stance in recommending/selling hood filters: They must be UL 1046 Listed, stainless steel, durable, and safe to handle. If grease extraction claims are to be compared, they must have been evaluated by a third party to ASTM Standard F2519-05. For regular cooking applications, this narrows it down to the following two options, either can be a sufficient choice depending on cooking style:
- Stainless Steel Baffle:
Pros: Long lasting, affordable, light weight, easy to clean, low noise, low resistance to airflow, safe to handle (no sharp edges).
Cons: Low grease extraction efficiency, (*bell-curve effect for airflow in hood. See section below for further explanation).
Pros: Long Lasting, high grease extraction efficiency, reduces *bell-curve effect for airflow, safe to handle (no sharp edges).
Cons: Expensive, can be difficult to clean onsite, higher resistance to airflow, heavier relative to that of a standard baffle design, can be noisy if hood requires high level of airflow.
Filters that should, in our opinion, never be used:
- An Unlisted filter: Presents a fire hazard. Beware of companies that actually sell these.
- Filters made of aluminum or galvanized metal: Do not hold up to cleaning/handling.
- Complicated filters that associate moving parts. (Hinged design, locking mechanisms, etc): These are constantly breaking in the field.
- Filters that are extremely difficult to clean: Efficiency extraction rates can look great on paper, but if the filters are too hard to clean, airflow exhaust airflow will diminish causing smoke rollout, and noise will increase at the filter.
Experiment: *The Bell-Curve Hood Airflow Effect: This is an undesirable effect associated with hood filters that have low resistance to airflow. To explain this, visualize a standard hood with one exhaust duct outlet at the top-center. With hood filters that have a low resistance to airflow (EX: standard baffle), air has an easier time flowing through the filter, thus at the center of the hood closest to the duct outlet, the velocity at this centrally located filter will naturally be higher. As you move further to the either end of the hood, the airflow rate will have a tendency to decrease simulating the shape of a standard bell curve when examining the entire hood filter velocity profile. With filters that have a higher level of resistance to airflow (generally those that are more efficient in extracting grease), this bell curve effect is greatly reduced and the exhaust airflow is more evenly spread out across the entire hood. Minimizing this effect is important, especially when there are high heat/smoke generating type appliances located towards the ends of the hood.
To demonstrate this bell curve airflow profile characteristic we performed a simulation in our test lab. In a standard wall canopy 8’ hood, we compared airflow face velocities across each hood filter in the entire hood for a filter with low resistance to airflow and a filter with high resistance to airflow. For the experiment, fan speed was held constant at 50hz for both tests. Face velocity measurements were taken with an Alnor 731 series digital airflow meter with 16 point 12×12” matrix at the center of each filter. One reading per filter, 6 total, left to right.
Test Setup #1: Stainless Steel Baffle Filter. QNTY 6, 20x16x2”.
Test Setup #2: Captrate Solo Filters. QNTY 6, 20x16x2”.
When analyzing the velocity profiles across each of the 2 scenarios, it is clear to see that the Captrate Solo Filter (higher resistance to airflow), does a much better job at spreading the airflow out evenly across the entire hood compared to the Standard Baffle Filter (lower resistance to airflow). This “Bell curve” type of airflow profile associated with the Standard baffle demonstrates how much variance in CFM there can be between filters depending on where they are located in the hood. In this example, the max velocity (filter near the center of hood) was 306 FPM, whereas the min velocity (filter near the end of the hood) was only 206 FPM. This is a major difference (149%) between airflow at the center of the hood compared to the end. In hoods that are longer (up to 12’ with one exhaust outlet), this difference in airflow is even greater. If this was a real life cooking scenario in an operating restaurant, you would definitely want the highest heat/smoke generating appliance located at the center of the hood. In many restaurants, grease will accumulate more readily towards the ends of the hood due to this drop off in airflow.
Before we completely bash the performance of the Standard Baffle filter compared to the Captrate Solo filter, one more characteristic should be looked at: Power. For this experiment, we were only interested in looking at the velocity profile across all filters in the hood. Fan speed was kept constant at 50 hz for both scenarios. The only thing that changed between the two tests was the Filter type, thus the Static Pressure drop across each filter (resistance). At constant fan speed a higher resistance to airflow will result in lower total airflow. In this experiment, if you look closely at the velocities, you will see that they are much lower for the Captrate Solo filter verses the Standard Filter. This means that the total airflow decreased when the higher resistance filters (Captrate Solo) were installed in the hood. Specifically, the total exhaust airflow for the hood was 3099 CFM with Standard Baffle Filters installed, and dropped to 2358 CFM with Captrate Solo’s. This is a difference of 741 CFM. If the total airflow was to be matched at 3099 CFM, the fan speed would need to be increased by 131.4%.
The 3rd Fan Laws tells us that power is a cubic relationship compared to speed/airflow. Thus calculating the required increase in power to achieve the same airflow rate of 3099 CFM with Captrate Solo Filters installed would be the following (Where P1 is initial power of motor at 2358 CFM of total exhaust airflow, and P2 is final required power of motor at 3099 CFM):
P2 = P1 x (CFM2/CFM1)^3
P2 = P1 x (3099 CFM/2358 CFM)^3
P2 = P1 x (1.314)^3
P2 = P1 x 2.27
The calculation shows that in order to achieve the same total exhaust airflow as the Standard Baffle filter when using Captrate Solo’s in the hood, the power consumption by the fan motor would need to be increased by 227%; over Double. Thus there is a cost associated with eliminating this “bell curve” effect; both in operating costs with increased power consumption and upfront cost of the Captrate Solo filter itself. Captrate Solo filters are definitely a higher quality filter and have much better performance than a standard baffle filter in regards to grease extraction and eliminating the bell curve effect, but it comes at a cost, both up front and operating. As the end user you deserve be aware of this.