Make-Up Air Units (MAU)

Make-Up Air Units (MAU): A Quick Overview A Make-Up Air Unit, or MAU, is a dedicated piece of HVAC equipment that brings in outdoor air to replace the air that is exhausted from a building. By supplying fresh air and distributing it throughout the space, MAUs help maintain indoor air quality (IAQ), control building pressurization, and ensure that ventilation meets code requirements. They are commonly used in commercial spaces such as restaurants, offices, schools, and light industrial facilities, where exhaust systems—especially large kitchen hoods and laboratory exhausts—remove significant amounts of air. How MAUs work An MAU typically operates by drawing in outdoor air through filters, conditioning it to a comfortable temperature and humidity level, and then delivering it to the occupied spaces via the building’s air distribution system. The unit often includes: - Filtration to remove dust and contaminants - Heating or cooling coils to condition the air - Humidification or dehumidification to control moisture levels - Dampers and control logic to regulate outdoor air intake in response to space needs and weather conditions - Optional energy recovery components (such as an energy recovery ventilator, ERV, or heat recovery ventilator, HRV) to transfer heat or moisture between incoming outdoor air and the exhaust air, reducing energy use In many facilities, MAUs are paired with exhaust systems. The exhaust removes stale or contaminated air, while the MAU replaces it with fresh air, helping to maintain a balanced or slightly positive pressure in the space. In kitchens and other areas with high exhaust flows, dedicated makeup air can prevent negative pressure that can pull in contaminants or cause malfunctioning doors and draft issues. Types and configurations Small MAUs come in several configurations, with the choice often driven by space, budget, and the required amount of outdoor air: - Packaged rooftop or indoor units: Compact, easy to install, and suitable for buildings with limited duct space. They can be placed on rooftops or in mechanical rooms. - Ducted MAUs: Located near the air distribution system, with ductwork delivering conditioned outdoor air to multiple zones. - Direct-vent MAUs: Bring in outside air directly to a specific area or zone, useful for spaces with predictable exhaust loads (like a kitchen hood or a single large room). - MAUs with energy recovery: Include ERV/HRV components to improve efficiency by recovering energy from exhaust air. Sizing and design considerations Proper sizing is essential. An oversized MAU wastes energy and can lead to uncomfortable drafts, while an undersized unit may fail to meet IAQ or pressurization needs. Designers consider: - The exhaust air flow rate from hoods and other equipment - Infiltration and building occupancy - Local climate and seasonal humidity - Desired indoor temperature and humidity setpoints - The potential for energy recovery to reduce heating and cooling loads Energy efficiency and IAQ Modern MAUs often emphasize energy efficiency and IAQ. Features to look for include: - High-efficiency filtration (MERV ratings suitable for the application) - Energy recovery (ERV/HRV) to recover heat or moisture - Variable outdoor air control that adjusts to occupancy or CO2 levels - Economizers that take advantage of cooler outdoor air when conditions are favorable Maintenance and operation Regular maintenance helps MAUs perform as intended. Key tasks include: - Replacing or cleaning filters - Inspecting and cleaning coils and ductwork - Checking dampers for proper operation and calibration - Verifying controls, sensors, and energy recovery components - Ensuring condensate drainage and addressing any unusual noises or vibrations Applications and benefits MAUs are versatile and beneficial in many settings: - Restaurants and commercial kitchens: Replacing large exhaust volumes with fresh air while managing odor and humidity. - Offices, schools, and retail spaces: Maintaining comfort and IAQ in spaces with varying occupancy. - Laboratories and healthcare support areas: Controlling IAQ and pressurization where needs are strict. - Industrial spaces with substantial exhaust: Balancing ventilation while controlling energy use. In short, a small MAU is a practical solution to keep indoor air clean, comfortable, and compliant with ventilation requirements. By selecting the right type, sizing it correctly, and pairing it with energy-saving features, buildings can maintain healthy environments without unnecessary energy waste.