HVAC (Heating, Ventilation and Air Conditioning) systems are designed to perform four main functions – heating, cooling, ventilation and controlling humidity levels. HVAC systems are designed to meet goals of its customers and satisfy them in terms of efficiency of system and saving energy. Many HVAC systems are available today and are designed for both homes to industries. Selection of HVAC system is critical because improper selection may cause discomfort in terms of health and loss of money. This article tells you about types of HVAC systems.
Though there are many type of HVAC units, there are four broad categories.
Constant air volume (CAV) HVAC systems
Constant air volume HVAC systems work by use of constant supply of air volume by distributing hot or cool air. Constant air volume HVAC systems are installed in large spaced rooms (auditoriums, theaters, lobbies, hospitals, manufacturing units, etc.). There are three variants of CAV systems: single duct, reheat and multi-zone systems.
- Single duct system: A single duct CAV is a simple central air conditioner with single zone distribution for either cool or hot air throughout the building at a fixed temperature (usually 55O F). This fixing of temperature allows to maximize cooling load in all spaces.
- Reheat system: The reheat system is modified single-zone distribution system that uses electricity or water to heat coils. Reheat coils reheat the cool air flow and distribute controlled air throughout the building. It is used in hospitals, laboratories and other buildings, which require wide load variation.
- Multi-zone system: Multi-zone system has two distribution systems, one for heating and other for cooling. Both ducts are designed to meet at one place called “mixing box”. This mixing box controls and distributes the required air temperature throughout the building.
Variable air volume (VAV) HVAC systems
Variable air volume systems are economical to install and are more energy efficient to bring down the cost by 10 to 20% compared to constant air volume systems. This system is best to meet varying cooling and heating needs of building areas.
The design of VAV system is simple and has small units that make installing easier. The main air duct provides cooling at 55O F and this is called primary air. A thermostat controls the temperature of primary air delivered to each room. This modulates the volume of air supply to get the required room temperature in different rooms according to cooling needs.
The main advantage of using VAV comes by its efficiency in dehumidification and temperature control by fan that efficiently reduces over all cooling or heating bills.
Radiant air conditioning (RAC) HVAC systems
Radiant air conditioning system refers to temperature controlled surface (hot/cold water or electrical heating coils tubing) that heats or cools indoor air temperature before air goes into the room. Radiating air conditioners install metal tubing on the surface of ceiling or walls of home or offices.
In this system, as air passes through metal pipes along the the concrete ceiling or walls, it gets warmed or cooled before it goes into the indoor environment. From these tubing, heat or cooling is transferred from ceiling or walls to warm the indoor air. The use of RAC has many advantages – no duct work is required, quite and energy efficient, no need of cool air exchanger, zoning capabilities and finally even temperatures for comfort. RAC is a power saving system that allows users to get comfortable temperature at home under lower temperature.
Advanced radiant RAC systems make it possible to control individual room in buildings. There are different types of radiant air conditioners and the most common types are electrical and gas fired systems.
Zoned system is a single area where temperature is regulated by singe thermostat. If a building’s temperature is controlled by a single thermostat, it is called single-zone. When multiple thermostats are used in a building, it is termed as multi-zone system.
In single zone HVAC system, single thermostat maintains same room temperature across different zones of same building. While in multi-zone system, each room is equipped with one thermostat to receive air with different temperatures based on the need of users.
Multi-zoned system is more advantageous over single-zone, as multi-zone system can efficiently control air-conditioning requirements. They are able to direct hot or cool air for certain rooms when needed. This offers wastage of power utilization for cooling or heating your building.
Use of zoning system enables you to save around 30% or more cooling/heating on power bills. Since zoned HVACs run based on your requirements at single or more rooms, it makes HVAC to run at lower speed and thus run quietly, and hence ergonomically good.
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