Indoor Air Quality Procedure: The Performance-Based Approach For example, the 2,400 cfm outdoor airflow calculated above cannot be reduced below 900 cfm. The most complex scenario is a multi-zone system with recirculation, where ASHRAE provides a detailed calculation procedure broken down by steps.ĭemand controlled ventilation (DCV) can adjust the outdoor airflow according to occupancy, but it cannot fall below the area-based airflow component. If the distribution effectiveness for the example above is 0.8, the zone outdoor airflow must be 3,000 cfm (2,400 cfm / 0.8).Ī single-zone ventilation system only requires one outdoor airflow calculation, and multi-zone designs without recirculation are based on a simple addition of individual airflows. It is then divided by the Zone Air Distribution Effectiveness, to obtain the Zone Outdoor Airflow that must be supplied by the ventilation system. This value is called the Breathing Zone Outdoor Airflow in ASHRAE Standard 62.1. Occupancy component = 7.5 cfm/person x 200 persons = 1,500 cfm.Area component = 0.18 cfm/sq.ft x 5,000 sq.ft = 900 cfm.If the area is 5,000 sq.ft and the restaurant is designed for 200 persons, the required ventilation rate is the following: The occupancy component is expressed in cfm per person.įor example, the minimum ventilation rate for a restaurant is 0.18 cfm/sq.ft.The design airflow per unit area is expressed in cfm per square foot.Based on air pollution research, ASHRAE has determined ideal ventilation rates for each type of building, which are presented per square foot and per occupant: The ventilation rate procedure is widely used, since it involves standardized calculations that are well-known in the HVAC industry. Ventilation Rate Procedure: The Prescriptive Approach Optimize your ventilation design and reduce energy consumption. While the VRP is based on prescriptive measures and ventilation tables, the IAQP is based on performance - delivering a ventilation system that controls air pollutants effectively. The VRP and IAQP follow different approaches to achieve a suitable ventilation level. The standard specifies a design procedure for natural ventilation, and two options for mechanical ventilation systems: the ventilation rate procedure (VRP) and the indoor air quality procedure (IAQP). The ANSI/ASHRAE Standard 62.1-2016 is called “Ventilation for Acceptable Indoor Air Quality”. ASHRAE standards cover many aspects of heating, ventilation, air conditioning and refrigeration, and building codes throughout the world use them as reference. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) was founded in 1894, and is has now evolved into a global association with over 50,000 members.
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