ACH@50

Definition:

ACH50 stands for Air Changes per Hour at 50 Pascals. It measures how many times the air inside a building is replaced with outside air in one hour when the building is subjected to a pressure difference of 50 Pascals. This metric is commonly used to assess a building’s airtightness during a blower door test. 

Short Description:

ACH50 quantifies the rate of air leakage in a building under standardized test conditions, indicating the building’s overall airtightness and energy efficiency.

Why It’s Important:

Understanding and measuring ACH50 is crucial for several reasons:

•Energy Efficiency: A lower ACH50 value signifies a tighter building envelope, reducing unwanted air infiltration. This helps maintain indoor temperatures, decreases heating and cooling demands, and leads to lower energy bills. 

•Indoor Air Quality: Minimizing air leaks prevents the ingress of pollutants, allergens, and moisture, thereby enhancing the indoor air quality and overall health of occupants. 

•Building Durability: Controlling air leakage reduces moisture ingress, which can prevent mold growth and structural damage, thereby extending the building’s lifespan.

•Comfort: Homes with higher ACH50 values will usually feel more drafty in the winter. In the summer, homes with higher ACH50 may have high humidity levels that makes the "feel-like" temperature too high for comfort.

Other Things to Consider:

•Building Codes and Standards: Many building codes specify maximum allowable ACH50 values to ensure energy efficiency. For instance, certain codes require new homes to achieve an ACH50 of 3.0 or lower, depending on the climate zone. 

•Testing Procedure: A blower door test is used to measure ACH50. This involves installing a fan in an exterior door to pressurize or depressurize the building to 50 Pascals and measuring the airflow required to maintain that pressure difference. 

•Improvement Strategies: To achieve a lower ACH50, focus on sealing gaps, cracks, and openings in the building envelope. Common areas for air leaks include windows, doors, electrical outlets, and ductwork.

•Balancing Airtightness and Ventilation: While a lower ACH50 indicates better airtightness, it’s essential to ensure adequate ventilation to maintain indoor air quality. Mechanical ventilation systems may be necessary in tightly sealed buildings to provide fresh air.

By understanding and optimizing ACH50, you can enhance your building’s energy efficiency, comfort, and durability.