Plus one assumes that one of the bedrooms has two occupants. Additionally, the formulas add 7.5 CFM per number of bedrooms plus one. The 2013 revision multiplies A floor by 3 CFM per 100 square feet, and later subtracts the measured/calculated air infiltration credit. The 2010 revision, then multiplies the A floor by 1 CFM per 100 square feet and assumes 2 CFM per 100 square feet of air infiltration. For example, if a house in a cold climate heats the basement, A floor would include the basement floor area. Therefore, the 2010 standard may under ventilate air tight buildings with less than 2 CFM per 100 square foot leakage.Ī floor refers to the conditioned floor area within the building envelope, excluding garages. Whereas the 2010 revision assumes a natural infiltration air flow of 2 CFM per 100 square feet of floor area. The standard then subtracts the infiltration airflow credit (determined from a blower door test, climate zone, and house type) to size the ventilation fan. The standard first sets the total airflow equal to the whole house ventilation airflow target. However, the 2013 and current revisions more accurately determine ventilation requirements. Upon first glance, it appears that ASHRAE decided to increase the ventilation requirements in their 2013 revision of the standard. The ASHRAE 62.2 total ventilation rate formulas below provide the buildings continuous ventilation rate requirements. The ASHRAE 62.2 Ventilation and Acceptable Indoor Air Quality in Residential Buildings standard details how to calculate ventilation rates. Their standards describe recommended practices in designing and installing HVAC equipment. How to calculate the required volume flow rate for mechanical ventilationĪSHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) is an organization that writes standards and guidelines for the HVAC industry. New or renovated homes with low natural air exchanges per hour require mechanical building ventilation to provide good indoor air quality. New windows, doors, and attic sealing / insulation tighten the building envelope and increase the buildings energy efficiency. New homes as well as older homes with building envelope upgrades/renovations have less natural ventilation. Homes with low natural air exchanges per hour require mechanical building ventilation to provide good indoor air quality. Better quality windows, doors, and attic sealing / insulation tighten the building envelope and increase the buildings energy efficiency. Houses built to newer standards as well as older homes with building envelope upgrades/renovations have less natural ventilation. Natural leaks may provide ventilation however, natural leaks are inefficient and result in high energy costs. The infiltration and exfiltration of air entering and exiting the building provide enough air exchanges per hour for good indoor air quality. Many older homes rely on natural leaks through windows, doors and cracks/holes within the building envelope for ventilation requirements. Ventilation requirements for older homes may not have needed mechanical building ventilation to maintain good indoor air quality. Balanced mechanical building ventilation is optimal for all climates. In addition to health concerns, proper selection of mechanical building ventilation can also protect the building structure.Įxhaust only mechanical ventilation performs better in cold climates whereas supply only ventilation performs better in hot, humid climates. These contaminants can become odorous, cause sensory irritation, and pose a health risk. The concentration of contaminants (toxins / pollutants) within indoor air can increase without proper ventilation. Indoor air quality improves by introducing fresh outdoor air while removing stale contaminated indoor air. Mechanical building ventilation provides better indoor air quality for the occupants. Purpose of mechanical building ventilation Wiring diagrams show how to interlock either an HRV or ERV with an air handler when they connect to existing building ductwork. Lastly, this article explains the differences between heat recovery ventilators (HRV) and energy recovery ventilators (ERV). Ventilation sequence illustrations show the state of the equipment (on/off, open/close) to demonstrate how mechanical building ventilation operates. Wiring diagrams show how to connect a ventilation controller to air handling units and bathroom exhaust fans. Additionally, this article has example calculations showing the differences between the ASHRAE 62.2-20 standard revision when sizing residential ventilation systems. This article explains the differences between exhaust only, supply only, and balanced building ventilation.
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