How Does a Make-Up Air Unit Work?
Providing a safe and healthy environment for employees continues to be a priority for manufacturing leaders, especially in facilities where manufacturing conditions create a potentially harmful environment for those working inside. Many manufacturing and industrial facilities that are plagued with poor indoor air quality typically do not have adequate ventilation. This lack of proper fresh air can create a variety of poor conditions such as high concentrations of harmful contaminants, hazy indoor conditions, improper process or product quality, OSHA safety violations, or even severe employee illness.
However, if your exhaust fans don’t also replace the air they take out of your building, you can very quickly end up with negative pressure, uneven heating or cooling, and even poor indoor air quality. This is where make-up air comes in handy. Utilized properly, make-up air units can bring in outside air while acclimatizing it to your building for safe, comfortable, quality indoor air. Learn more about how make-up air units work in this guide by the experts at Cambridge Air Solutions.
Why is Make-Up Air Needed?
The first step in solving your Indoor Air Quality issues for your manufacturing environment is a properly sized mechanical exhaust system, preferably located nearest to the source of indoor contaminants. The rate of exhaust airflow or amount of fans may vary due to the process or the type of contaminant. As the exhaust fans capture, contain, and expel these harmful gases, a deficit in fresh air is created.
If you don’t replace that air, you end up with:
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Negative building pressure (doors are hard to open, outside air gets sucked in through cracks)
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Drafts and cold or hot spots
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Poor indoor air quality and humidity issues
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Combustion safety risks; fuel-burning appliances (water heaters, boilers, unit heaters) may not draft properly if the building is starved for air
What Does a Make-Up Air Unit Do?
Make-up air units supplement the normal exhaust fan process by also intentionally bringing outside air into a building or workspace while simultaneously conditioning it. This helps to further lower the concentration of harmful elements created by industrial processes, and replace the air removed to maintain high-quality indoor air. This also helps balance building pressure and reduces humidity issues.
Components of Make-Up Air Units
Most MUAs share the same core pieces:
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Outdoor air hood and filters
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The unit draws in 100% outside air.
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Intake hood and filters keep out debris, insects, and larger particulates.
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Dampers
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Fan/Blower
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A supply fan pulls air through the unit and pushes it into the duct system or directly into the space.
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Many units now use VFD's (variable frequency drives) to ramp fan speed up or down based on demand.
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Heating section (and sometimes cooling/tempering)
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Common heating options
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Direct-fired gas: Burner is in the airstream, very efficient, often used in industrial spaces.
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Indirect-fired gas: Burner heats a heat exchanger, the air does not contact combustion gases.
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Hot water/steam coil: Tied to a boiler system.
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Electric heaters: Less common for large volumes due to energy costs
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Some units also have:
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Discharge section / ductwork
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Conditioned air is discharged through ductwork or a discharge plenum.
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Air can be distributed across the space or targeted to problem areas (doors, production, lines, etc.)
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Controls and sensors
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Temperature sensors (outdoor and supply air)
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Building pressure sensors (to maintain neutral or slightly positive pressure)
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Airflow switches, freeze protection, safety limits
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Control panel with BMS integration or standalone controller
The Make-Up Air Process
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A make-up air unit works by pulling in fresh outside air, conditioning it, and pushing it into the building to replace air that has been exhausted. When exhaust fans, kitchen hoods, or process equipment pull large amounts of air out, the unit senses the demand (or is interlocked with that equipment) and starts up. Motorized dampers open, the fan begins moving air through an intake hood and filters, and the system measures the incoming air temperature against a supply air setpoint.
From there, the heating (and, if equipped, cooling) section “tempers” the air so it is comfortable before it enters the space. On a cold day, the burner or coil ramps up to warm the air; on milder days it may just provide ventilation with little or no heat. The fan then distributes the conditioned outside air through ductwork or a discharge plenum into key areas of the building. Controls monitor building pressure and adjust airflow so the space stays neutral or slightly positive, helping doors operate properly, reducing drafts, and maintaining better indoor air quality.
Why Make-Up Air Solutions Should Evolve As You Do
Adding a make-up air unit to your facility is a must to keep it comfortable and productive if you utilize processes during manufacturing that introducing harmful gasses or particulates into the air.
However, a proper ventilation strategy shouldn't stop there. As many manufacturing environment needs and processes change, they fail to add the necessary tempered make-up air units, resulting in poor temperature control, uncomfortable cold spots, and sometimes poor product quality.
In these situations, a right-sized make-up air solution can bring in the clean air that is direly needed. This type of system not only improves the quality of air within the building to meet ASHRAE and local standards, but also protects the health of the employees. However, this requires taking both your specific building, manufacturing processes, and average climate into account. A functional right-sized make-up air solution needs to be able to take the coldest expected outdoor air temperature and warm it up to a usable supply without running at its limits all the time.
Engineers typically consider: total exhaust CFM, desired building pressure, climate (design winter/summer conditions), building size and use, leakage, and duct/static pressure. When all of that is balanced, you end up with a right-sized make-up air unit that quietly does its job—replacing exhausted air, supporting indoor air quality, and keeping people comfortable without wasting energy.
Why Install Make-Up Air Units from Cambridge Air Solutions?
Cambridge M-Series 100% direct-fired units are the most efficient way to offset building exhaust and improve Indoor Air Quality by introducing fresh clean air from outside. Our Make-Up Air units are designed with reliability and energy savings in mind, along with low costs for installation and maintenance. M-Series heaters include patented Cambridge Low-Fire Start Technology and proprietary stainless steel burners, are specifically designed to provide year-round ventilation and tempered make-up air for a wide variety of commercial and industrial facilities.
With CFM ranges from 1800 – 75,000 available and the ability to customize the system to your facility, these units are utilized across the United States in applications from tire factories to paint booths to food processing plants.
Schedule a Building Walkthrough Tour with Cambridge Air Solutions Today
Do you feel like your facility is working against you? When the air in your facility is too hot in the summer, too cold in the winter, or too contaminated from your manufacturing process, you can turn to Cambridge Air Solutions for support and guidance. Join us for an Air Solutions tour customized to address your specific questions regarding how our technology can help you address your facility challenges. Your knowledgeable Cambridge guide will walk you and your team through our facility and answer any specific questions you may have regarding make-up air.
Ready to get started? Schedule a building walkthrough today! One of our Cambridge engineers will tour your facility and discover the exact needs of your building and your employees. Then, we’ll help create a make-up air systems specifically tailored to help you unlock your building’s fullest potential.
Schedule a Walkthrough of Your Building