Variable Air Volume or VAV Boxes is the most common method employed in commercial/institutional buildings and is both an effective and economical means of temperature control by Regulating the Air Flow. AV systems have proven to be highly energy efficient in providing an optimal indoor climate. The latest standards and requirements for energy efficiency and human thermal comfort make it more and more challenging to design new HVAC systems which comply with these standards. Energy could be saved reducing primary air volumes to a minimum during reduced load conditions. But in traditional VAV systems, this could cause “cold air dumping” and lack of air movement in the room, resulting in occupants' discomfort and a consequent decrease in productivity. Induction VAV is the perfect solution for maintaining proper air circulation and comfort levels, reducing the primary treated air to a very minimum (20% of maximum). Room air will be induced without the use of an additional fan and induction VAV guarantees that the required standards for comfort will always be achieved.
CAV unit operates the fan and compressor at full capacity until the temperature drops to a specified setting, then the compressor turns off. The on/off cycling is not efficient at keeping the space at a constant temperature. These systems are small and serve a single thermal zone, however, variations such as CAV with reheat, CAV multizone, and CAV primary-secondary systems have the ability to serve multiple zones and larger buildings. Mainly two types of CAV systems are commonly used, the terminal reheat system and the mixed air system, the terminal reheat system cools the air in the air handling unit down within its zone of spaces. It cools the air but is inefficient and costly. The mixed air system comprises of two air streams, among which one is for the coldest and one for the hottest needed air temperature in the zone. The air streams are strategical combines to offset the space’s load. It works well to cool the air but it does not control humidity.
The simplest VAV system controls air from a single supply duct and varies the airflow to each zone or room based upon the temperature in the room.
From a control perspective, such a system would consist of a few essential components :
In some instances, these components are combined. For example, a Smart Thermostat can combine the functions of a Temperature Sensor and a Controller.