Cubic feet per minute (CFM) is a measurement used to quantify the flow rate of air or gas in a system. It represents the volume of air that passes through a specific point in the system in one minute. CFM is commonly used in various industries, including HVAC (Heating, Ventilation, and Air Conditioning) systems, to assess airflow rates and ensure proper ventilation.
CFM in HVAC systems plays a crucial role in determining the effectiveness and efficiency of the ventilation process. Proper ventilation is essential for maintaining indoor air quality, controlling temperature and humidity levels, and ensuring the comfort and safety of occupants in a building.
Importance of CFM in HVAC systems
- Ventilation: Proper ventilation is essential to maintain a healthy and comfortable indoor environment. CFM helps to ensure that an adequate amount of fresh outdoor air is brought into the space and that stale or polluted air is removed. This process helps reduce indoor air pollutants, control humidity, and replenish oxygen levels.
- Air distribution: CFM plays a significant role in distributing conditioned air throughout a building. It helps maintain consistent temperatures across different areas and ensures that all occupied spaces receive sufficient heating or cooling.
- Energy efficiency: By accurately calculating the required CFM for a given space, HVAC systems can be designed and operated more efficiently, leading to energy savings and reduced operational costs.
- Equipment sizing: Knowing the required CFM allows for proper sizing of HVAC equipment such as fans, ducts, and filters, preventing overworking or underperforming systems.
Overall system performance
Ways airflow within an HVAC system can be impeded:
- Blocked or restricted air vents: Furniture, curtains, or other obstacles can block air vents, reducing the airflow into a room and disrupting the balance of the system.
- Clogged air filters and coils: Dirty or clogged air filters and coils can impede airflow through the HVAC system, reducing its efficiency and potentially causing damage to the equipment.
- Improperly designed or sized ductwork: Inadequate or poorly designed ductwork can create bottlenecks and friction, limiting the airflow and decreasing the overall system performance.
- Closed or obstructed dampers: HVAC systems often have dampers that control airflow to different zones or areas. If these dampers are closed or obstructed, it can disrupt the air distribution.
- Inadequate fan performance: The fan responsible for moving air through the system may not be operating optimally due to issues like motor problems or imbalanced blades.
Air handler units
How to Find and Correct Concerns with CFM:
- HVAC Assessments: Routine inspection and assessments are helpful to stay in front of any issues that affect CFM in HVAC Systems. Assessment data identifies air handler units that need to be cleaned, repaired and optimized.
- HVAC Steam Cleaning: Fouled coils and blowers reduce airflow. Therefore, it is important to regularly clean them. However, over time dirt and debris is deeply deposited into the coils. HVAC steam cleaning uses high temperature and low pressure steam to blast through the coils to restore airflow.
- Environmental Duct Cleaning: When equipment located within the duct system such as VAVs, reheat coils and dampers becomes fouled airflow is also restricted. Not all duct cleaning scopes are the same. Be sure to specify the inspection and cleaning of inline equipment when contracting duct cleaning.
- HVAC Restoration: Removing old and inefficient blowers and replacing them with modern ECM fan arrays is a viable option to improve airflow. Fan arrays also provide operational redundancy since there are multiple small fans installed into the new bulkhead wall.
It’s crucial for mechanical engineers, HVAC professionals and facility managers to consider CFM and its implications while designing, installing, and maintaining HVAC systems to ensure proper ventilation, indoor air quality, and energy efficiency. With over three decades of experience, WTI – Pure Air can assist users in assessing and correcting the CFM in HVAC systems in the buildings.
