Reaching a balance between the supply air and return air is crucial to ensuring that the indoor air quality of your building remains at its highest. One way you can do this is to make sure that your building’s HVAC system has enough static pressure. Static pressure refers to the difference in pressure readings between two areas, typically taken at different heights or on opposite sides of an opening.
In the world of HVAC, the difference in pressure between two points can be caused by two different factors: a difference in air density and a difference in air velocity. While the two are related, they are not the same thing.
Static pressure is slightly different from pressure drop. Static pressure looks at the total amount of resistance that a fluid experiences as it travels through an opening or duct. In contrast, pressure drop shows how much resistance is experienced in one specific place along that duct system.
Static Pressure and Air Density
While the terms “static pressure” and “air density” are often used interchangeably, they are not the same. When air travels through an opening or duct, it experiences a change in air density. So, where two areas of the air encounter one another, that change in density affects the overall pressure levels of a building. As the saying goes, molecules close together have more potential for collisions than those far apart. It is through these collisions that indoor air quality can be affected.
Air density can be measured in units of kg/m3 (kilograms per cubic meter) or PCF (pounds per cubic foot). Units of air density are often referred to as pressure per volume. Because air has weight, one kilogram of air has an equal amount of force as one kilogram of weight placed on top of it. When you divide the weight in kilograms by the unit volume, you get an accurate measure of how much pressure is exerted on any given area.
This means that it is possible for two volumes of air traveling through the same opening to have different pressures. If the density of air were to increase, the pressure would decrease. If the density of air were to decrease, the pressure would increase.
Air Velocity and Static Pressure in HVAC
Air velocity is one factor that contributes to static pressure in HVAC systems. The speed of air strongly influences how the air travels through a duct system. If air moves at 8 mph, for example, the pressure drop in the duct can be reduced by about 10% (a small decrease in static pressure). But if the air moves at 50 mph, pressure drop in the duct can be reduced by about 80% (an even larger decrease in static pressure). It is important to understand that air velocity increases the chances for air density to change within a given length of duct.
It’s also important to understand that more force can be exerted on one area of air than another. When air is divided into sections, the force is felt more strongly in one section than another. This is more than just a change in air density—a pressure drop occurs at one specific point.
Air velocity can be measured in FPM (feet per minute) units. Typically, buildings have a maximum recommended airspeed and duct size for a given area. If the air moves too quickly through the duct and becomes too dense, it can cause significant problems.
Air velocity is one of the main factors that affect static pressure. If an HVAC system has a high air velocity, it will have high static pressure. However, if the air moves at a slower speed and becomes denser, the pressure will be lower.
How Static Pressure Affects Indoor Air Quality in Your Building
You may wonder how this affects your indoor air quality. Well, pressure is not the only factor that affects how clean the indoor air is in your building. Other factors include the following.
The Number of Contaminants in the Outside Air
The higher the concentration of these contaminants, the greater the number of molecules present. This means more collisions between molecules that lead to a change in air density, which increases the level of particles in indoor air quality.
Environmental Conditions Such as Temperature and Humidity
When there is a significant change in temperature or humidity levels, it can affect airflow patterns within your building’s duct system and cause trouble with your HVAC system.
The Airflow Within the Ducts
How your HVAC system’s ducts are designed and constructed will affect how they handle airflow. If your HVAC system has fewer small, hard-to-get-to spots or if it has spaces between the units where the air has nowhere to go, then small particles may build up in those places.
The Air Filter
If you have an air filter, it will extract particles from the air and clean it. This is important because many particles are too small to be seen by the naked eye. If they are not cleaned, they can act as a breeding ground for bacteria, viruses, and mold in your HVAC system.
The HVAC System’s Airflow Rate or CFM
If the HVAC system moves a lot of air, it can help keep the indoor air cleaner, but it may not be enough to remove all particles from the air. That’s why your HVAC system must have a high airflow rate (CFM) and be easy to access and use. Filters are an essential part of this equation.
The HVAC System’s Static Pressure Drop and Static Pressure Buildup
If the airflow of your HVAC system is not high enough, it could mean that you have a higher level of particles in your indoor air. The higher the level of particles in your indoor air, the more likely it is that you will experience problems such as asthma or allergies.
The Number of People Present in Any Given Space at Any Given Time
This factor also affects the level of particles in your indoor air. If you live in a space with many people other living and working there (such as an office building, dormitory, or hotel), the number of particles floating around can be higher than if you lived in a single-family home.
How Do I Reduce Static Pressure in My HVAC System?
There are ways to reduce static pressure within your HVAC system. This will help to reduce the number of particles in your indoor air. Have an air cleaner or filter in your HVAC system. You can install a filter in your ducts with the help of a professional from Bel-Aire Heating & Cooling to help reduce static pressure and particle build-up by removing the contaminants from the air and filtering it clean enough for you to breathe.
Contact a Professional
When experiencing problems with your HVAC system in the surrounding areas of Portage, Three Rivers and Grand Rapids, MI, you should seek professional help from us at Bel-Aire Heating & Cooling. Our technicians provide HVAC service and repairs that are done correctly and done to code. In addition, we provide furnace installation and repairs, AC repair and replacement, and home energy audits. If you have any questions or would like to request an appointment, contact our team at Bel-Aire Heating & Cooling today.