Name: ________________________________
MCHE 4650
Chapter 6 – Comfort, IAQ, Climate Data
Summary of the “Ventilation Rate Procedure” to get outdoor ventilation air requirements
defined for an HVAC system
1. Compute the required ventilation to the breathing zones in each room connected to the air
handling unit. (Rp and Ra values from Table 6-1 of ASHRAE Standard 62.1)
𝑉𝑏𝑧 = 𝑅𝑝 ∙ 𝑃𝑧 + 𝑅𝑎 ∙ 𝐴𝑧
2. Compute the room or zone outdoor airflow based on the zone air distribution
effectiveness (Ez). Ez from Table 6-2.
𝑉𝑜𝑧 = 𝑉𝑏𝑧 /𝐸𝑧
3. If this unit serves only one room, then that is the total amount of outdoor air needed.
4. If this is a 100% outdoor air unit (for example with a dedicated outdoor air system) that
serves more than one room, the total amount of outdoor air is the sum for all rooms.
Vot = Σall zonesVoz
5. If this unit is a multiple-zone (room) recirculating system (most common type for a
typical commercial building), then must adjust for the system ventilation efficiency (Ev).
a. Compute the primary outdoor air fraction for each room/zone (Zpz).
𝑍𝑝𝑧 = 𝑉𝑜𝑧 /𝑉𝑝𝑧
Vpz is the primary airflow to each zone (room) for cooling or heating purposes
b. Determine the maximum primary outdoor air fraction for all zones (rooms)
connected to this unit, and determine the system ventilation efficiency to be used
for this unit from Table 6-3 (below).
c. Compute the uncorrected outdoor air intake as sum total of rate to breathing zones
for all rooms/zones connected to this unit.
𝑉𝑜𝑢 = 𝐷 ∑
𝑎𝑙𝑙 𝑧𝑜𝑛𝑒𝑠
(𝑅𝑝 ∙ 𝑃𝑧 ) + ∑
𝑎𝑙𝑙 𝑧𝑜𝑛𝑒𝑠
(𝑅𝑎 ∙ 𝐴𝑧 )
Uncorrected airflow does not account for zone air distribution effectiveness, but it
probably should.
D =”Occupant Diversity” = Ps /Σall zones Pz
or, D = “Fraction of max. occupancy that this system is actually designed for”
d. Total outdoor air intake computed based on system ventilation efficiency
𝑉𝑜𝑡 = 𝑉𝑜𝑎 /𝐸𝑣
Документ1
Rev. 4: 5-January-2020
Name: ________________________________
Документ1
Rev. 4: 5-January-2020