Classification- HVAC System
Considering you know what HVAC is,in this article we are going to read about what are types of HVAC.
Mainly there are two types of commercial HVAC.
01. Single zone system
02. Multiple zone system
(First take note that the classification of a particular system in this period may not apply to how that system is used in every application. In some systems, however, the unit ventilators may have the capability to operate at multiple fan speeds.)
Single-Zone Systems
A single zone, constant volume system delivers a constant quantity of air to a single, temperature controlled zone. The thermostat measures the dry bulb temperature within the zone and compares it to the desired set point. In response to a deviation from that set point, the thermostat sends a signal to vary the cooling or heating capacity of the system. Because the supply fan delivers a constant quantity of air to the zone, this reduction in cooling or heating capacity varies the temperature of the supply air at part load conditions.
If the zone is comprised of multiple conditioned spaces, the space in which the thermostat is located dictates the operation of the HVAC system. All other spaces must accept the resulting level of comfort based on the space containing the thermostat. If the thermostat calls for more cooling, all spaces get more cooling.
Therefore, in a building with this type of system, it is common to use several single-zone systems to satisfy the different thermal requirements of the building.
A simple example of a single-zone, constant-volume system is a packaged terminal air conditioner (PTAC). This type of equipmentcontains several components of the airside loop and all the components of therefrigeration, heat-rejection, and controls loops inside a common casing.
Multiple-Zone Systems
The previous section discussed systems in which the supply fan delivers air to a single thermal zone. This next section will discuss systems in which the supply fan delivers air to multiple, individually controlled thermal zones.
Again, within this multiple-zone category, systems will be further classified by whether the supply fan delivers a constant volume or a variable volume of air.
A multiple-zone, constant-volume systemuses a central supply fan andcooling coil to deliver a constant quantity of air to several individuallycontrolled zones. The central cooling coil cools and dehumidifies the supply airto a particular leaving-air temperature. In some systems, this temperature isconstant; in others, it varies throughout the day and year based on a particularexternal condition, such as outdoor temperature.
A multiple-zone, variable-volume (VAV) systemconsists of a central air handler that serves several individually controlled zones. Each zone has a VAV terminal unit (VAV box) that is controlled by a thermostat in the zone. Unlike a constant-volume system, which delivers a constant amount of air at varying temperatures, a VAV system delivers varying amounts of constant temperature air. A thermostat in each zone compares the dry-bulb temperature to a set point, and the VAV terminal responds by modulating the volume of supply air to match the changing cooling load in the zone. Meanwhile, the central supply fan modulates to maintain a constant pressure in the supply ductwork, and cooling capacity is modulated to maintain a constant supply-air temperature. Heating can be accomplished in several ways.The first approach is to install a heating coil (hot water, steam, or electric) or a gas-fired burner in the central air handler. In this configuration, the system can operate similarly to the changeover–bypass system and switch to delivering warm supply air during the heating season. A second approach is to install individual heating coils inside the VAV terminal units. Each coil is controlled by the zone thermostat to warm up the supply air when necessary. A third approach is to install perimeter baseboard radiant heat within the zone, which can also be controlled by the thermostat.
The first example of a multiple-zone, variable-volume system is the packaged rooftop VAV system.A large, packaged DX rooftop unit islocated outdoors and contains several components of the airside loop, as wellas all the components of the refrigeration and heat-rejection loops. A buildingmay use a single rooftop unit or several units, depending on its size, loadcharacteristics, and function.
