Ventilation Efficiency Indices

Ventilation efficiency has traditionally been defined as the ratio between contaminant concentration in the occupied spaces and the concentration in the exhaust air. Sandberg and Skaret differentiate between the terms air change efficiency and contaminant removal effectiveness. Air change efficiency is a measure of how effectively the air present in a room is replaced by fresh air from the ventilation system, whereas contaminant removal effectiveness is a measure of how quickly an air-borne contaminant is removed from the room. A third similar criterion that is used is contaminant removal efficiency.  

In the current review, the term effectiveness of air distribution will be used to describe the ratio of the occupied zone area (where thermal comfort and contaminant concentration are within ranges required by standards and codes) to the total occupied zone area. This hygienic criterion allows one to judge how well the HVAC system fulfills its main task—creating thermal comfort conditions and controlling contaminants in the occupied zone. 

Industrial halls are typically large enclosures—indoor spaces that typically comprise one or more zones of occupancy. A large height combined with heat sources often results in room airflow patterns controlled by buoyancy flows, 

A characteristic of many industrial halls is that zones of occupancy take up only a small portion of the room volume and height. In addition, the flows are normally buoyancy dominated. This results in a vertical temperature stratification that can be utilized for room air conditioning design in order to achieve effective climatization along with low energy consumption. 

A process is found effective when it produces a desired effect e.g., ventilation in a room is effective when it produces sufficiently good air 

---

A review of ventilation efficiency indices is given below. Complete mixing ventilation is the comparative basis for all efficiencies, with the value 1.0. That may be useful, as complete mixing ventilation often is assumed in early design phases. 

Ventilation efficiency Indices that provide a method of assessing the mixing characteristics of incoming air with the room air. It presents a means of determining the pollutant distribution within the space. 

Which ventilation efficiency index should be chosen for assessment depends on the actual scenario in the enclosure. 

Due to the assumption of well-mixed air, room ventilation efficiency studies also cannot be performed. However, a multizone ventilation efficiency index for the whole building may be determined. 

---