What we measure: differential pressure in buildings

Emily Moschowits
August 3, 2021

According to recent reports, in order to keep global warming below the threshold of 2°C, the building sector would need to be net carbon zero by 20501. As carbon emissions from this sector currently exceed that from all forms of transportation, we are a long way from this goal2

Globally, buildings consume 55% of electricity and energy use in commercial buildings accounts for 6.6% of CO2 emissions3, three times emissions from deforestation globally4. So what can we do about it? Read on to find out more.

1. What is differential pressure?
2. Why is it important to monitor and control the differential pressure in your building?
3. What affects differential pressure in your building?
4. How to manage differential pressure in your building

1. What is differential pressure?

In the open, the air pressure comes from the weight of the air molecules in the atmosphere pushing down on you. Inside buildings or any closed container, the air pressure tells you how much the air pushes on the walls of the container and everything inside of it. Air pressure depends on temperature and concentration of air molecules in the building. 

Pressure, generally, is the force exerted over a given area5, while air pressure represents how much the air molecules push on everything around them6. Differential pressure describes the difference between the air pressure in two different areas, for example, inside and outside of a building. This helps you understand and predict the airflow and prevent air leakage from your building. 

Air, like people, tends to move away from high pressure situations, if possible. Without something stopping it, like a knot tying a balloon shut, the air inside will escape, moving from high pressure to low pressure. The relative pressures inside and outside of buildings are constantly in flux, meaning air continually tries to move either in or out of your building. 

2. Why is it important to monitor and control the differential pressure in your building?

Buildings use 71% of the electricity and 54% of the natural gas in the US, and they’re also responsible for 40% of the country’s greenhouse gas emissions, according to Berkeley Labs7. Fixing leaky buildings can therefore have a huge potential to reduce wasted energy. 

Even small changes in differential pressure can impact airflow and noticeably reduce the comfort and longevity of your buildings. Not only does the draft of the airflow itself detract from the indoor environment, but negative pressure differences can lead to higher concentrations of VOCs, CO2, particulate matter, and even microbes inside your building8. It’s commonly thought that commercial buildings are more airtight than their residential counterparts. However, research has found that in practice this is not true9. Therefore, for all buildings, it is crucial to understand what your differential pressure is and for the majority of buildings, it’s important to ensure that your business maintains a differential pressure of 0 to avoid the negative consequences of uncontrolled airflow. 

Before the Covid-19 pandemic, 30% of a building's energy was consumed through ventilation and leakage of air. Now that people are returning to work and buildings are increasing ventilation rates to reduce the risk of viral spread, this is expected to increase the energy intensity of buildings10.

Energy leakage

Whenever there is a difference in pressure between the inside and outside of a building, air will leak out of the building or get sucked in from the outside. This can cause several issues. 

In the winter, when the hot air leaks through any spaces in the building's facade, it’s as if money is flying out the window with it. Heating a building can be very costly. What’s more, heating and cooling is responsible for 40% of the energy use in buildings11. In total, building operations accounted for 28% of global energy-related carbon emissions12 and 55% of global electricity consumption13. Reducing this wasted energy can greatly reduce the carbon footprint of your building.

Temperature stability and building comfort

Drafty rooms are uncomfortable, for your tenants, employees, visitors and whomever else occupies your space. If people feel uncomfortable, they will often turn up the heat in the winter or AC in the summer, even if this doesn’t directly fix the problem. Stabilizing the temperature and minimizing the draft is a key way to reduce energy consumption overall and make people feel more comfortable. People perform better14, and even pay more for items15, when they are in comfortable surroundings. Feeling uncomfortable due to drafts caused by a lack of airtightness in buildings can lead to increased energy consumption16. It can also cost you, as the building owner or facilities manager both time and money17

Air quality is impacted

Air quality can also suffer when a building is not airtight. The differential pressure that causes air to move in and out of your building will bring with it outdoor air pollutants, harmful airborne chemicals (VOCs)18, or dangerous elements, such as Radon19. You can see this as dust and particulate matter sometimes accumulates on the inside of window frames. On the other hand, if a building is too airtight and there is not sufficient ventilation, indoor air quality can also suffer from the buildup of CO2 and other contaminants inside the building20

Building quality 

Beyond the immediate issues caused by a lack of airtightness, you must also consider the long-term consequences. The difference in air pressure and temperature between the inside and outside of a building can lead to condensation in between the walls. As more water accumulates, the damp interior creates an ideal environment for mold growth. In addition to the harmful health effects of mold, this also reduces the lifespan of your building. 

When thinking of the life of a building and all the energy and natural resources that go into it, most people think of turning off the lights or reducing the AC in the summer as ways to help the environment. But it is also important to consider all of the resources necessary to construct the building in the first place. If the condensation reduces the integrity of the building, then it could need more repairs over its lifetime and mean that the whole building will need to be replaced sooner, impacting your carbon footprint and your wallet.

Learn more about how you can use the  Airthings for Business solution to monitor your buildings Facility managers, get in touch   

3. What affects differential pressure in your building?

There are three main elements impacting the air pressure differences in buildings: wind, the stack effect, and ventilation. While the first two are not controllable, managing the third with the correct data and technology can improve the balance in your building. 

Wind blows around buildings, changing the air pressure on the outside, altering the pressure differential. Air is pulled into some parts and out of others. Although this is not always a huge issue, it can be especially problematic in very windy areas, and the only potential solution is to block the wind with other buildings or planting tall trees to provide cover21

The stack effect, aka the chimney effect, is aptly named. This is a naturally occurring phenomenon due to physics and gas laws. Basically, warm air rises, increasing air pressure in the top of the building22. This pushes some air out. As air exits the top part of the building, the change in air pressure at the bottom will draw more cold air into the building. This new cool air will be warmed, again causing it to rise and repeating the process. This effect has an additional downside. Not only will this increase your energy bills and your carbon footprint as you constantly need to heat more air, but also the air being sucked into the bottom of the building could contain dangerous chemicals such as radon23

These two natural phenomena can’t be prevented but they can be counteracted by proper use of a smart ventilation system. Mechanical ventilation systems are designed to move air into, out of, and around buildings. They are vital for maintaining the comfort of the indoor environment by regulating CO2 levels, temperature, and humidity. However, most systems are not smart enough to take into account differential air pressure on their own. As a result, they can waste extra energy heating or cooling additional air that is being pulled into the buildings as the tempered air is leaking out. One way to fix this would be to improve the airtightness of buildings. However, this could be extremely expensive, especially in older buildings24. What’s more, if a building is too airtight and lacks a proper ventilation system, there is a risk for poor indoor air quality as stale air can be trapped inside. Therefore, it’s necessary to measure differential air pressure, monitor indoor air quality, and react to imbalances to ensure maximal comfort and efficiency in buildings.

4. How to manage differential pressure in your building

Airthings Balance for Business makes balancing the differential pressure in your building easy. By measuring the pressure both inside and outside using our proprietary sensors and our cloud-based algorithms, we can alert you to differences in pressure. When integrated directly into your building’s ventilation system, it can dynamically adjust airflow to minimize the pressure differential. This will help you save both money and time, as well as minimizing your impact on the environment.

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