Proper building pressure is essential for your buildings as it can affect many different areas, including security, indoor air quality, structural health, occupants’ comfort, energy conservation and freeze prevention. Whether it’s over- or under-pressurization, this can be costly in terms of energy and disruptions for occupants and building managers alike.
Building pressure is impacted by several factors, including weather conditions, height of the building, how well the building is sealed (particularly at the top), and the operation of the mechanical systems. We have no influence on the weather conditions or the height of the building, but we can control how well the building is sealed and how we operate the mechanical systems.
During the cooler months, the “stack effect” in a building can behave like a chimney–cool air enters at the bottom of the building, warms up and then rises up through the building. This cycle can be slowed down by making sure that the exit points through the upper floors and roof are closed and sealed. Places to look are dampers in stair and elevator shafts. Also make sure that all doors exiting the stairs are gasketed and are closed. If the air can’t get out, then the outside air will not come in.
Remember, you are always exhausting air from your building. Toilet exhaust and other general exhaust can be calculated and measured. It is important to always deliver more outside air to the building than the exhaust air through the mechanical systems. This will assure that overall the building will be in a positive pressure condition.
We often witness buildings that are prone to frozen piping and water coils. The damage realized can be costly and disruptive to the occupants in the building and the staff. The good news is that this can be avoided when the building is in a positive pressure, the control system is functioning and the dampers close tightly. Many building engineers close all of their outside air dampers in an attempt to “save” their coils from freezing. This may help the coil, but it guarantees that infiltration will create other unintended consequences. Infiltration is also a big problem during warmer and higher humidity conditions. Moist air infiltrating the structure will reach dew point, condense on the building’s structure, and provide the conditions for physical damage. Infiltration can also cause mold and allow for water incursion during rainy conditions.
Concerned? Then take these simple steps:
- Check for air exfiltration from your building and repair.
- Measure how much air you are exhausting.
- Assure that you are delivering at least 10% more outside air.
- Check controls, freeze stats and dampers on all air handling units.
- Monitor your systems and controls, and never take anything for granted.
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