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. 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. (PDF) Ventilation for Acceptable Indoor Air Quality Home Atmospheric Sciences Air Quality Atmospheric Pollution Geoscience Indoor Air Quality Book Ventilation for Acceptable Indoor Air Quality.Determine zone air-distribution effectiveness E Z by looking up Table 6.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).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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