![]() Several of the identified published studies reported ventilation rates. Minimum ventilation rates in ASHRAE 62.1-2004 versus ASHRAE 62-1989 thru -2001 Occupancy category Required ventilation, cfm/1000 ft² Changea 62-1989 thru -2001 62. Because carbon dioxide concentrations often exceed 1000 ppm by a wide margin, the data indicate that ventilation rates in classrooms are often far less than 7 L/s (15 cfm) per occupant. Now the required rate is based on the number. For variable air volume system s, the design outdoor ventilation rate at the system level must always be maintained even when the fan has modulated to its minimum capacity. determining the breathing-zone ventilation rate (Vbz). This is acceptable considering that the concentration of pollutants in the overventilated spaces return air is low enough that it can be used, along with the ventilation to the other spaces, to dilute pollutants in those spaces. One air handler serving many zones with recirculation, all zones receive the same percentage of outside air, resulting in some zones being over ventilated. Multiple – zone system: Ventilation is satisfied by provid ing, at minimum, the outdoor air that represents the sum of the ventilation requirements at each space that it serves.100% outdoor air system: One air handler serving many zones without recirculation system outside air requirement: Vot = ΣVoz.Single – zone system: One air handler serving one zone system outside air requirement: Vot = Voz.System calculations: Calculate outdoor air intake flow for the entire system, based on prescribed calculation procedure. Voz = Vbz / Ez (outdoor air in the space breathing zone divided by zone air distribution effectiveness).Calculate outdoor airflow to the zone.Determine zone air-distribution effectiveness E Z by looking up Table 6.Mechanical exhaust required and the recirculation of air from such spaces is prohibited. Vbz = Rp x Pz + Ra x Az (outdoor flowrate per person by number of people plus outdoor flowrate per square foot by area of the zone). MINIMUM VENTILATION RATES For SI: 1 cubic foot per minute 0.0004719 m 3 /s, 1 ton 908 kg, 1 cubic foot per minute per square foot 0.00508 m 3 / (s m 2 ), C (F) -32/1.8, 1 square foot 0.0929 m 2.Calculate outdoor airflow to the breathing zone, using Table 6.Zone calculations: Determine breathing zone outdoor airflow for each zone, based on prescribed rates in ASHRAE 62.1 Table 6.2.2.1
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