The Importance of Make-Up Air

Many industrial facilities use processes that can heat-up the work floor in a building. Appropriately designed ventilation systems will combat this heat with fans or vents. However, the use of these systems to draw air out of the building also creates negative pressure inside.

A building with negative pressure will begin to draw in air from the environment in any way possible including doorways, wall seams, and cracks in window openings. Excess air infiltration can cause cold zones to develop at the building perimeter (See Figure 1). As a result, parts of the building will be comfortable but other parts will be much colder or hotter than intended. This phenomenon will occur whether or not provision is made for this replacement [1].

Importance of Make-Up Air — *Figure 1 – A building experiencing negative pressure due to unbalanced Exhaust system.*

The Importance of Understanding Negative Pressure

Negative pressure in a facility has a significant impact on worker comfort and building efficiency. Furthermore, the larger the pressure difference caused by unbalanced ventilation system, the faster the air will infiltrate the building. Negative pressure can create cold zones (See Figure 2) which can manifest in a number of negative effects.

Cold zones caused by negative pressure in an industrial building — *Figure 2 – Additional Heating Equipment in Cold Zones*

Effects of Negative Pressure in An Industrial Facility

CROSS-DRAFT AND POOR AIRFLOW	Cross-Drafts, especially fast cross-drafts, can interfere with the natural operation of ventilation stacks, carry contaminated air to different parts of the building, and even interfere with proper operation of process equipment.
OVERWORKED EXHAUST FANS	Excess intake air in a negative pressure building makes exhaust fans work harder. This extra work increases the energy needed for the fans to operate properly and increases the frequency of breakdowns.
EXTRA EQUIPMENT COST	Cold zones on the perimeter of the building will prompt building owners and operators to purchase additional ventilation and heating equipment to balance out the building’s temperatures.
WORKER (DIS)COMFORT	High velocity drafts coming in at entryways / windows will create uncomfortable conditions for workers. In the winter, they may be exposed to frigid air blowing on them as they work.

The Importance of Make-Up Air for a Real Ventilation Solution.

The solution to this issue is to introduce outdoor air to the space in a controlled fashion, via the use of Make Up Air (MAU) units. When sized to balance the amount of air exhausting A MAU will eliminate any pressure difference between the building and the environment.

MAUs, like the Moffitt Make-Up Air (MMA) unit, also include the option of tempering the air before entering the building, lessening the load on existing facility HVAC systems. The resultant uniformly heated building will eliminate the “cold zones” that were previously an issue (See Figure 3).

Uniformly heated industrial building serviced by a make-up air unit — *Figure 3 – A Uniformly heated building serviced by a Make Up Air (MAU) Unit*

Heating + Make-Up Air

In addition to balancing air-pressure, a make-up air unit can also be fitted with a natural gas heater to warm the incoming air. A heater, whether direct-fired or indirect-fired, will heat the air as it is introduced into the building. This prevents the system from bringing in air that is too cold for the workers to properly do their jobs.

Moffitt Make-Up Air in Action

For over sixty-five years Moffitt has helped industrial facilities find their perfect ventilation solution. Our team handles vents, fans, cooling, and heating for factories throughout North America and the world. Contact our team today to see how your building can benefit from a new ventilation solution.

[1] Chapter 7 of the Industrial Ventilation Handbook, A Manual of Recommended Practice, 21^st Ed. American Conference of Governmental Industrial Hygienists (ACGIH)