Makeup air units are crucial in today’s commercial spaces; they’ve even trickled into the residential market in the form of air purifiers and similar systems. Although they are critical to maintaining proper oxygen levels and removing contaminants from outside air, they can be misunderstood in terms of their usage and placement within an overall HVAC system.
Essentially, HVAC exhaust fans remove air from buildings and makeup air units pull in fresh, oxygenated air to replace it. Without makeup air units, HVAC systems would have to draw fresh air through gaps in the building itself, which is both less effective and less efficient. Makeup units also incorporate filters, which purify air.
However, building a makeup unit to specification can be a complex process. They must be able to work with the outside ambient temperature in order to heat or cool the air to a comfortable temperature and humidity level.
Each room has different expected ventilation needs based on exposure to chemicals and irritants in the air and the amount of physical activity performed in that location. For example, the California Building Code notes that dining rooms and conference rooms must have a ratio of 0.5 cubic feet per minute of airflow for every square foot of the room. In more active spaces, like casinos or dance floors, those requirements jump up to 0.68 and 1.07, respectively.
Makeup air units are vital throughout these spaces simply because the only alternative for ventilation is windows that are open to the exterior. While this explains the common practice of grouping rooms in insular hubs in certain retail environments or in schools, it simply is not feasible in a scenario like a mall or an office complex. There, to meet local, state, or national requirements, as well as the standards set by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, makeup air units must be incorporated to meet airflow ratios.
Educational settings are an interesting situation for HVAC engineers because they do not have very stringent requirements in terms of minimum outside air, and no requirements in terms of how much air must be brought in from outside. Instead, ASHRAE specifies 15 cubic feet of air per minute per person per room. For example, a classroom with 20 students would require 300 cubic feet of air per minute.
Makeup air units are also invaluable in enclosed spaces with potentially dangerous fumes like science labs or auto shop classrooms. They also regulate both humidity and condensation, preventing potential damage to the rest of the HVAC system.
Hospitals are among the most complex facilities in terms of ventilation requirements for different types of rooms. For instance, a ground-floor lobby would have different ventilation needs than an office, an exam room, or even a cafeteria. The most stringent requirements regarding makeup air units come from the Centers for Medicare & Medicaid Sciences’ guidelines for operating rooms.
There, they state that humidity levels be at least 20 percent, with 20 air changes per hour, four of which must be completely outside air. Best practices from ASHRAE and the Association of Operating Room Nurses offer a max limit of 60 percent relative humidity and more outside air.
In addition, most burn units, operating rooms, and isolation units must keep positive pressure relative to adjacent rooms. This helps contaminants from entering those rooms and improves outcomes for patients. Makeup air units can help pull air out of the rooms as necessary and replace it with filtered, uncontaminated air.
For each of these cases, specifying the right makeup air units is crucial, as is designing a system that adequately accounts for the amount of outdoor air necessary to meet these stringent regulations.
If you’re designing an HVAC system, you probably have a few considerations in mind—your heating and cooling system should be reasonably priced, easy to maintain, and reliable. Makeup air units are an ideal choice, and Windy City Representatives can help you choose the right unit from a trusted manufacturer for you.