4 factors that impact HVAC pressure

An HVAC system accounts for 40 per cent of a building’s total
electricity consumption, according to the Energy Efficiency Exchange. Building
managers should ensure the equipment is operating efficiently or risk wasting a
considerable amount of energy at significant cost.

Regular inspections must be carried out by HVAC technicians to check the
system’s pressure and airflow. Pressure fluctuations, which can impact a
system’s performance, can be caused by multiple factors. Here are four
variables that affect HVAC system pressure:

1. Outside pressure

A seemingly unlikely cause of pressure fluctuations in HVAC systems is air
pressure from the outside of the building. Specifically, when a facility’s
pressure is negative, the equipment can pull in exorbitant amounts of
unconditioned air. In contrast, positive pressure can force conditioned air out
of the building.

HVAC technicians can take advantage of this relationship by setting the
pressure at around 25 Pascals during summer. However, professionals shouldn’t
ignore how certain facilities use natural ventilation to create adequate

2. Leaky ducts

A leaky duct is another possible cause of pressure fluctuations in HVAC
systems. According to Building Green, small fractures or leaks in an HVAC system’s
ductwork can cause pressure to build up in some areas and decrease in other
sections. This imbalance creates uneven airflow, impacting overall performance
and efficiency.

However, such leaks can be detected by HVAC technicians using pressure
measurement instruments capable of identifying anomalies. These checks
should necessarily be carried out by builders following any renovation work in
a building, especially on ductwork near renovated areas to ensure contractors
didn’t accidentally damage it.

3. Fan settings

The balance between relief and intake airflow is another factor that influences
the building’s internal pressure. If the inflow vents absorb more air than what’s
expelled by the building, the HVAC system will create a net positive pressure.
This may be desirable, depending on the season.

4. Wind

Wind can push outdoor air onto one side and pull indoor air from the
leeward direction. Depending on outdoor air density, building height and nearby
obstructions such as trees and other structures, this variable can also cause pressure

To mitigate the detrimental effects of high winds, facility managers
should consider maintaining negative building pressure. Conversely, positive
pressure should be maintained during periods of low winds.

Test and measurement equipment specialist testo advises building
managers to regularly check HVAC system pressures and also consult with testo’s
experts on the best pressure measurement instrument for their application.

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