Make Up Air Units - The Basics

In this video, I discuss the basic components of a Make-Up Air Unit.

These types of systems are also known as 100% OA Units, OA Units, Dedicated OA Unit, DOAS Systems, Dedicated MAU, and many other names.

The basic function is to cool, heat, dehumidify and sometimes humidify outdoor air before bringing it into a building. Outside air is required to make up for the exhaust leaving the building otherwise you will have a negative pressure which can lead to infiltration, mold, and mildew issues.

The OA unit must be able to accomplish these overall load conditions, during all seasons of the year. Features like modulating hot gas reheat, modulating compressors (digital scroll, variable-capacity compressor (VCC) or VFD Compressors), modulating condenser fans and the proper application-specific controls are a must.

Email Me: Tony Mormino

About me:
I sell commercial air conditioning equipment in Western North Carolina (Greater Asheville). I also sell AC equipment to national corporations through AAON's National Account Program. My passion for teaching and giving back to the HVAC community has inspired me to create free educational videos, virtual lunch and learn presentations, and webinars.

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Email Me: Tony Mormino

Thank you for watching and please let me know if you have any questions!

[wernerbrandes]

Hi, your video is great, I wish the hvac Specialist for our Building could learn from this.
The common hallway for our apartment building went from 16 degrees Celsius to 23 degrees C but the humidity is extremely low, it’s below 20% or more and causing an instant headache from getting off the elevator.
They’ve supposedly been here 3 times and lowered the temp 6 degrees F each time for the heat on the make up air unit with no improvements to either temp or humidity. (Actually it dropped 0.5 degrees Celsius) but the humidity is still extreme.
Shouldn’t it be as simple as allow more outside air to mix with heated air? Or is it more complicated than that. It’s 32 degrees F outside.
I’m questioning the competency of the hvac company, however, they are a large name. It’s 3 visits and zero difference?! To make it cooler to around 70 F and have about 40 -45% humidity from 73.4 F and less than 20% humidity (20 is the lowest my thermometer is able to display at which then only shows Low) I’m concerned for my health and there are a number of people with disabilities living here, myself included.

Any advice would be golden

Thank you for your video

[abazism]

Thank you so much for your clear explanation.

[rayertman]

Very clear and to the point. Thanks. I will be looking through more. I have a couple problems i need to solve re negative pressure cleanrooms that all compounding pharmacies must be USP 800 compliant due to newly implemented regulations. Current system not enough to account for 12 ACPH which is the requirement for Level C non sterile room. I believe I'm going to require supplemental source of air and trying to get a grasp on the process. Seems like the HVAC 'cabal' has this info very well guarded lol.

[potentialhvac]

I work in San Francisco doing Commercial HVAC service. I noticed most the make up air units that I come across don't have any means of dehumidification ( at least not at the RTU), one doesn't even have a heat source and is only used if these large exhaust fans kick in due to heat on the 4th floor. My thought is that the ones I work on where done cheaply to save cost but some times I feel like it's just poor design. In some of these cases it seems like these building spaces would be a lot more comfortable if things had been done with the MAUs done correctly

[nimbo]

I think in the winter mode, it would be good to have a humidifier as well not just only a heating coil.

[TAHIRHUSSAINMEPINDUSTRY]

how to add pre-treated cool fresh air in HAP program

[vsolcar]

I figured that on a hot day you'd want to keep that 50° blowing into the inside. 72° sounds way too hot.

[riccardobertolino]

Hi! is there any pro/cons between outdoor make up air units and indoor one? gas plumber are very expensive and bring the natural gaz line up to the roof top maybe an issue... also many told me that electric heated make uo air are very expensive on bills, espcially in Canada where temperature go down to minus 20 easily in winter. someone can answer me?