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What Are HVAC Systems? – A Brief Guide

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The HVAC system

HVAC is short for Heating, Ventilation and Air-Conditioning. These are mechanical systems that provide thermal solace with indoor air quality. It is an integral part of residential and commercial units including homes, apartments, hotels, hospitals and vehicles such as trains, cars, airplanes and ships. The HVAC system can be categorized into central and local systems.

  • Primary HVAC system: It includes heating equipment, ventilation equipment and cooling equipment 
  • Central HVAC system: It is installed away from the building in the central equipment room and delivers chilled air through a duct system. It contains three systems: all air, air- water and all water systems.

Local HVAC systems are inside the conditioned zone and it does not require any ductwork. It includes local air conditioning, split systems, local heating and local ventilation.

The selection of an HVAC system depends on three main factors: the building configuration, the climate conditions and the owner’s desire.

Basic components of an HVAC system:

  • Mixed air plenum and outdoor air control
  • Air filter
  • Exhaust fans and an air outlet
  • Supply fan
  • Outdoor air intake
  • Duct system
  • Return air system
  • Heating and cooling systems
  • Cooling tower
  • Boiler
  • Water chiller
  • Humidification and dehumidification unit

Classification of an HVAC system:

It is of two types: local and central systems. 

  • Central system: Its major equipment is installed outside the zone and in a central location.
  • Local system: Some buildings or a single zone unit need equipment to be installed inside. This is common in residential apartments and small homes because small houses and apartments require a local HVAC system. The example of these local systems includes an air conditioner to cool a bedroom or an electric heater in a room. It only needs a one-point control connected to a thermostat to activate the local HVAC system.

The most common type of AC fused in single homes is a central forced-air conditioner. 

Mini-splits:      

Mini-splits are cooling and heating systems that allow to control the temperatures in single rooms and spaces. It has two main parts: an outdoor compressor and an indoor evaporator. They only need a three to four-inch hole through a wall for the conduit. These are of great benefit as they are ductless and require only a small space conditioning system. Their replacement parts are easily available too. One such company is Younits.com. They have a wide variety of mini-splits. The popular ones include Daikin ductless mini split systems, Daikin XS24LVJU 24k BTU Cooling + Heating Wall Mounted Mini Split System, Mitsubishi MZ-FH12NAH Heat Pump Mini Split System – Hyper Heat w/ Base Pan Heater, Mitsubishi SE-KA12NA.TH Slim Duct Mini Split System etc. 

Boilers:

A boiler not only boils water, but it also turns water into steam and pumps it through the home. This helps in keeping the unit hot. Boilers work as a heat potable water and depend on the thermostat to indicate when to start heating. Most boilers work on the mechanism of closed-loop systems as they do not use new water to heat units. Water is kept inside the boiler. Once the water starts heating and turning into steam, the boiler spreads the heat throughout the home. 

There are three main types of vent available: chimney venting, power venting, and direct venting. High- efficiency boilers maximize the amount of heat by undergoing the process of condensing. They are 10% more efficient than non-condensing boilers. Condensing boilers can work with high- temperature systems. The most used fuel for a boiler is natural gas. Boilers with an efficiency between 80% – 84% AFUE are standard boilers. AFUE rating tells about what percentage of fuel is used by a boiler. Most of the boilers use a cast-iron heat exchanger and chimney venting. 

Water heaters:

As the name indicates, water heaters heat water. It takes water directly from the water pipe and warms it up. The heated water is available for the entire unit. Water heaters come with a tank that takes cold water and indirectly warms it by electric heating rods or gas burner. Then this heated water is stored inside a tank and is readily available when a person opens a shower or tap. There are five main types of water heaters.

  • Conventional storage-tank water heater – It is most widely used 
  • Tankless water heater
  • Hybrid water heater; heat pump water heater
  • Solar-powered water heater
  • Condensing water heater  

Refrigerants:

Refrigerant is a mixture; a fluid that is used in a heat pump and refrigeration cycle. Many fluids are used in refrigerants such as fluorocarbons especially carbon fluorocarbons CFC but the use of CFC is declining due to their ozone depletion effects. Other common refrigerants are ammonia, sulfur dioxide and propane: a non-halogenated hydrocarbon.

Refrigerants mainly work by undergoing a phase transition from liquid to gas and then gas to liquid again. Refrigerants are composed of the following main parts: the compressor, condenser and an evaporator. All these parts are linked together. 

The mechanism is as follows:

The refrigerant flows through the compressor and during this flow the pressure of refrigerant rises. It then enters the condenser where the refrigerant condenses from vapour to liquid form In the next phase, it enters the evaporator where the pressure of refrigerant drops and it cools down. The refrigerant then goes back to the compressor to restart this cycle. Refrigerants are commonly used in air conditioning systems, chemical and pharmaceutical companies and food industries.  

  • Guardian 407C Units:

There’s a new refrigerant that is more compatible with R22. It is 407C. Guardian R407C is offering ACs with capacities of 1.5 through 5.0 tons in comparatively lower prices instead of using R410A that has a short live compressor and coil replacement problem.

In this article, many types of air conditioning systems are discussed that have their pros and cons. Ductless mini-split is usually preferred over central air conditioning units as it is ductless and contains only two components. Another type of air conditioning is PTAC or packaged terminal air conditioner, they are found in hotels or upper-end apartments. It consists of a small compressor, a heat exchanger coil and a blower that work together. However, they are not as efficient as a ductless or central air conditioning unit. 

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