Does HVAC mean Central Air?
For most people, it is really hard to tell the difference between HVAC and AC. This is because the two terms are used interchangeably almost everywhere.
But what is the difference between AC and HVAC? Is HVAC same as central air? What are the components of each and how do they work?
HVAC stands for heating, ventilation and air conditioning while AC stands for air conditioning. An HVAC systems therefore cools, heats and regulates a house’s air quality while an AC unit only cools the house.
Air conditioning (AC) is one of the three components of an HVAC system (heating, ventilation and air conditioning). An AC can be a standalone unit or it can be paired with a furnace, ductwork and vents to form an HVAC system.
Although HVAC has many components, AC (cooling) and furnace (heating) are the 2 main components. Others include thermostats, ductwork, vents, dampers, air filters etc.
But Central air also has ductwork! So, how different is an HVAC system from central air conditioners?
HVAC does not necessarily mean central air. Central air conditioners comprises of a condenser unit, an evaporator and ductwork to cool the whole house. However, an HVAC system will comprise central air components as well as a furnace/air handle, ductwork and vents.
Air conditioning (AC) is the process of removing heat from the house to the outside. You need to heat exchangers (coils), one inside the house (evaporator unit) and another outside the house (the condenser coil).
And what about split AC? What is the difference between split AC and HVAC?
Split ACs have one big condenser unit outside the house and several inside units, one in each room for cooling the house. Split systems can however be heat pumps, meaning they can heat and cool the house in which case they would become HVAC systems after factoring in ventilation.
HVAC however does not include a water heater. As a matter of fact, a water heater is part of the plumbing system (hot water supply system).
Unknown to some, HVAC does indeed include refrigeration. The principle behind refrigeration is the exact same one as air conditioning. An HVAC technician will therefore be well versed with refrigeration tasks.
HVAC vs AC
Now that we have seen the main difference between HVAC and AC, let us now look at how all of the different processes in an HVAC system work, since AC is part of HVAC
1. Air Conditioning
As I have already mentioned, air conditioning is the process of removing heat from indoor air and releasing it outside the house. I also mentioned that in order to do that, we need an indoor heat exchanger and outside heat exchanger.
There are many types of air conditioners which include:
- Central air conditioners
- Ductless/mini-splits
- Window air conditioners
- Portable air conditioners
No matter what type of air conditioner you have, the principle behind how they operate is the same. To explain how ACs work, I will use 2 of the most common types, central air and ductless ACs.
Air conditioners use a chemical with a low boiling point but high latent heat of vaporization called a refrigerant to transfer heat from inside the house to the air outside the house.
The 3 components of an AC (condenser, compressor and evaporator) are connected using copper tubes and the refrigerant is circulated between them where it changes state from gas to liquid and back to gas again as heat exchange is carried out.
Inside the house where the evaporator coil is located, a cold refrigerant liquid enters the coil as a fan is pulling hot indoor air towards it. The hot indoor air absorbs heat from the refrigerant and that is how it is cooled.
As the cooled air is circulated back to the house, the refrigerant evaporates and flows out towards the compressor.
The compressor compresses the refrigerant gas to increase its pressure, but an increase in pressure also translates to an increase in temperature.
It is important to increase the temperature of the refrigerant so that heat can flow from the refrigerant to the surrounding air.
Remember: In heat transfer, heat is transferred from a point of high concentration to a point of low concentration.
From the compressor, the refrigerant enters the condenser coil (both the condenser coil and compressor are located outside the house in one big metal cabinet).
A fan blows cooler outside air over the coil. The air absorbs heat from the refrigerant and takes it away into the surrounding air. By the time the refrigerant is exiting the coil, it will have condensed into a liquid ready to go back inside the house for more cooling.
The cycle is repeated over and over again until the house is properly cooled.
2. Heating
While air conditioning is important during the summer, heating is the homeowner’s concern during winter. There are 2 main ways to heat a house:
- Furnace
- Heat pump
Furnace
A central air conditioner is in most cases usually paired up with a furnace. Furnaces run on natural gas primarily, but they could also use propane or oil.
Cold air from the house is pulled to the furnace using return air ducts and after heating the heated air is supplied using the supply air ducts. The indoor temperature is monitored using a thermostat.
Heating starts when the thermostat signals the furnace to kick in. An electronic ignition starts the burner component inside the combustion chamber.
The flames from the burner component then heat a metal heat exchanger. The heat generated circulates through the looped tubes of the heat exchanger. As the air moves across the tubes, it absorbs heat from the heat exchanger and that is how it gets heated.
Heat Pump
A heat pump can cool and heat the house. When used to cool the house, a heat pump works exactly like and air conditioner. As a matter of fact, it is hard to tell a heat pump from an AC by just looking at them. Just like in air conditioning, there are 3 main types of heat pumps:
- Central air – One unit outside and another outside which heats the whole house to the same temperature. This can be fixed using HVAC zoning systems.
- Ductless/split system – One outside unit and several inside unit. Each room can be heated/cooled a temperature different from the other.
- Packaged units. All the components (condenser, evaporator and compressor) are housed in one big metal cabinet installed outside the house and connected to the ductwork directly.
Heat pumps works (when used to heat) by extracting heat from the outside air. Even when the outside air is really cold, it still has thermal energy which can be extracted and used to heat the house.
Heat pumps have a device called a reversing valve which reverses the direction of flow of the refrigerant during heating operations. As such, a very cold refrigerant enters the condenser coil outside the house.
Since it will be way colder that the outside air, heat will be transferred from the air to the refrigerant. Because refrigerants have a low boiling point, it will evaporate and enter the compressor in gas state.
The compressor will compress the gas which will also increase its temperature. A high-pressure superheated gas therefore enters the evaporator coil inside the house. The indoor air absorbs heat from the refrigerant which is then circulated throughout the house. That is how heat pumps heat the house
3. Ventilation
Ventilation is basically the process of removing stale air from a space and intentionally replacing it with fresh outdoor air. Activities such as breathing, washing, cleaning, showering, cooking etc. make the indoor stale, saturates it with particles and also increases humidity.
Ventilation therefore makes sure that this air is constantly being replaced with outside fresh air. That prevents you from becoming ill or even mold/mildew from growing indoors/ There are 2 types of ventilation:
- Natural ventilation
- Mechanical ventilation
Natural ventilation is when exchange of air between the inside space and outdoors happen naturally. This includes opening windows or doors to the space which allows “communication” with the outdoors.
Mechanical ventilation is when air is forced out and inside a space. This process is then one mainly used in HVAC.
Opening windows might work but they reduce the efficiency of your air conditioner during summer and your heating during winter.
HVAC systems have vents and fans which bring in outside air inside the house and also remove stale air to the outside. Due to the ductwork network, ventilation in central air conditioning is way better than that in ductless/split systems.
Wrap Up
And that is how HVAC is different from AC. I hope that this guide was helpful and that it left you with no gaps in as far as HVAC and air conditioning is concerned.