Types of HVAC Systems

There are four different types of HVAC systems: single zone, multiple zone, constant volume, and variable air volume. Single-zone unit can only serve multiple building areas if they have similar heating, cooling, and ventilation requirements, or if the system can compensate for differences in HVAC requirements. Each area regulated by a single thermostat is referred to as a “zone.” If the system’s design does not account for differences in heating and cooling loads between rooms, occupants may experience discomfort. This generally happens for one of two reasons. The cooling load changes due to increased lighting, or introduction of heat-producing equipment or people, or areas within a certain zone have different solar exposures. These factors produce radiant heat gains and losses that create unevenly distributed heating or cooling needs. Multiple-zone systems, on the other hand, provide each zone with air at a different temperature by heating or cooling the air stream in each zone. These systems are designed to deliver air at a constant temperature while varying the volume of airflow, or by modulating the room temperature with a supplementary system such as baseboard heating. Constant volume systems work by delivering a constant flow of air to each space. Changes in space temperatures are achieved by heating or cooling air, or switching the air handling unit on and off. Constant-volume systems are often required to operate with a fixed minimum percentage of outdoor air, or with an “air economizer” feature. Variable air volume systems keep spaces at a comfortable temperature by varying the amount of heated or cooled air delivered to each space, rather than by changing the air temperature. However, many of these systems allow for the temperature of the delivery air to be reset on a seasonal basis, depending on the weather. For example, you may want to set the air temperature at 72 degrees in the winter, and 70 in the summer. Be aware that overheating or overcooling can occur within a given zone if the system is not adjusted to respond to the load. Underventilation generally occurs if the system is not arranged to introduce at least a minimum quality (instead of percentage) of outdoor air as the system dials down from full airflow, or if the system supply air temperature is set too low for the loads present in the zone. Wondering which type of HVAC system is right for your office space? Contact us with any questions you might have.