Understanding How Residential HVAC Systems Work
by The Cooling Company, on Oct 3, 2019 10:22:18 PM
If you’re like most people, your only interaction with your HVAC system is turning it on and off. You know little about how it works and probably don’t care to know. All you care about is that it keeps you cool during the hot Las Vegas summers and wards off the chill on cold winter nights.
It is, however, always good to have a basic understanding of how a residential heating and cooling system works to help troubleshoot HVAC problems and make it easier to explain it to the HVAC technician. Knowing how everything works together can also help you better maintain the system. Here’s our complete guide to how a residential HVAC system works.
The Different Parts of an HVAC System
HVAC stands for heating, ventilation, and air conditioning. Most homes in Las Vegas have a central heating and cooling system but many homeowners don’t fully understand how it works.
There are four types of HVAC systems: split systems, packaged units, heat pumps, and ductless mini-split systems. Traditional split systems are comprised of indoor and outdoor units that are attached to an extensive ductwork system that runs through the house to air vents in each room. Packaged systems and heat pumps are contained in one unit and ductless systems, as the name suggests, don’t require ducts. All central air systems are controlled by the thermostat.
To gain a better understanding of how a central air system works, let’s take a look at the main parts that make up a residential HVAC system.
The condenser, located in the outdoor unit, is where heat transfer takes place. The condenser is comprised of the compressor, condenser fan motor, coils, and control board. To start the AC’s cooling process, the refrigerant flows through the coils while the fan pulls in air and as this air blows over the coil, it helps dissipate heat from the coils.
When problems arise with the condenser unit, it can usually be traced to the fan, motor, capacitor, dirty or bent condenser coils, or damaged fan blades. When the condenser fan doesn't work, the refrigerant in the coils can't be cooled. An AC that isn't blowing cold air is a sign that there could be a problem with the condensing unit.
The role of the compressor
The compressor in the condensing unit is what drives your air conditioner. It is commonly referred to as the “heart” of the air conditioner as it is responsible for pumping refrigerant through the system. Without refrigerant, your air conditioner won’t be able to produce cold air.
The compressor is powered by a motor. Both these components work hard and are subject to a tremendous amount of wear and tear. It’s important to make sure you are diligent about checking the outdoor unit periodically as dirt and grime can build up on and around the compressor and motor, placing them under extra strain. The compressor is one of the most expensive parts of an AC to replace. To avoid unnecessary breakdowns, keep the area around the outdoor as clean as possible and schedule regular AC maintenance with your HVAC company.
The evaporator coil is mounted in or above the air handling unit inside your home. The air handler and furnace are often located in the same place.
Copper pipes carry refrigerant from the condensing unit outside to the evaporator inside. This is where the cool air you feel in your home comes from. By the time refrigerant gas reaches the evaporator, it has changed into a cool liquid. Warm air passes over the cold evaporator coils that vaporize the refrigerant liquid and turns it back into a cool gas that absorbs heat from the air and cools it. This cool air is then distributed through the ducts and out through the vents into your home. The heat collected from inside is absorbed into the coils as a part of the circulation process.
The role of the blower motor
The blower motor is part of the evaporator coils. If the air conditioner runs but no cold air is coming from it, it usually indicates a faulty blower motor. Contrary to what many believe, air conditioners don’t produce cold air. They simply transfer heat from one area to another, and the blower is the crucial component that directs this heat transfer.
The blower fan sucks in warm air, passes it over the evaporator coils where it cools, and returns the cooled air to the room. When the blower malfunctions, no air circulates through the system. This can lead to serious problems, like the evaporator coils freezing over. If this happens to your system, shut off the AC and call a technician who will check and repair the blower.
The furnace is typically located in a basement or attic. The most common type of furnace in most central heating systems is natural or propane-powered gas furnaces.
Both the air conditioner and furnace connects to the home’s ductwork. A gas furnace is made up of the following parts:
- A gas valve
- Ignition switch and burner
- Heat exchanger
- Exhaust outlet
The thermostat is the “brain” of the HVAC. It senses temperature and tells the AC or furnace to start running when the temperature of the air in the home no longer matches the temperature set on the thermostat. Once the desired temperature is reached, the thermostat turns off the AC or furnace. When the temperature drops or increases, the thermostat will start another cycle.
How a Residential Air Conditioner Works
Air conditioners work on a simple physics principle of liquid that expands into gas to pull heat from its surroundings. Evaporation aides the cooling process. Let’s explain this in more detail.
Your air conditioner uses refrigerant gas. Refrigerant is crucial in turning warm air into cold air. Refrigerant runs through the AC condenser coil located in the outdoor unit to the evaporator coil in the unit inside the house. When you turn on the air conditioner, low-pressure refrigerant gas starts the cooling cycle in the compressor where it is “compressed” into a hot, high-pressure gas. This pressurized gas flows through the condenser coils where it is “condensed” into a high-pressure liquid. At the same time, the condenser fan blows over the coils and removes excess heat out into the air.
The hot liquid then passes through an expansion valve where the pressure is lowered. This low-pressure liquid flows into the evaporator coil where it cools and changes back into a low-pressure vaporized gas. As it does this, it absorbs heat from the surrounding air, leaving behind the cool air that is blown through the ductwork and into your home. The heat absorbed from the house’s air is carried back to the compressor where it is expelled to the outside, and the whole cycle starts again.
How a Furnace Works
There are three types of furnaces: gas, oil, and electric. Gas and oil furnaces use fossil fuels like natural gas, propane, or oil to generate heat while electric furnaces run on electricity only. In Las Vegas, most homes feature a gas furnace that connects to the city’s natural gas lines.
A gas furnace works in the following way:
- The gas valve is linked to the control board which links to the thermostat. When you turn the furnace on, the thermostat communicates with the control board and activates the gas valve. The valve opens just long enough to release enough gas to ignite the burner.
- The thermostat continues to sense temperature changes in the home and “instructs” the control board to open or close the gas valve as required. As the air in the house warms up, the valve will narrow to reduce heat. As the air cools down and more heat is required, the gas valve will widen.
- The flame from the burner sends heat to the heat exchanger where it transfers that heat to the cold air it pulls in from the room, warming up the air.
- Warm air is distributed throughout the house by the blower and fan. It flows through the ductwork and into the house through the vents.
How a furnace’s combustion gas is expelled from the house
When gas furnaces generate heat, they produce combustion gases, like carbon monoxide gas, that must be removed from the house. Carbon monoxide gas is highly toxic and, when inhaled, can be fatal. For this reason, every furnace has an exhaust outlet, like a chimney flue or vent, to allow combustion gas to exit the house.
When an exhaust outlet becomes blocked by soot or dirt, carbon monoxide gas can build up to dangerous levels. Carbon monoxide is an invisible and odorless gas that makes it hard to detect through smell alone. This is another reason regular HVAC maintenance is important. On a routine maintenance check, the HVAC technician will inspect your furnace to make sure safety controls are functioning properly and that the exhaust outlet isn’t blocked or restricted in any way.
As an extra safety precaution, consider installing a carbon monoxide detector. If you smell any gas or the carbon monoxide detector alerts you, shut off the furnace and call your utility company or the fire department.
The “V” in HVAC stands for ventilation. Most homeowners focus mainly on the heating and air conditioning function of an HVAC system and give little thought to how ventilation affects a home’s comfort levels and air quality. Too little ventilation and your home will start to feel stuffy. Poor ventilation can also lead to allergies and health problems due to a build-up of bad air that may contain dust, allergens, and bacteria.
The biggest issue with poor ducting is that it causes the system to break down. Ducts that are too small ducts make the system work hard and burn out faster, and ducting that's too large won't have enough resistance for the system and also cause it to burn out.
Residential HVAC systems are designed to heat, cool, clean, ventilate, humidify, and dehumidify your home. One easy way to circulate some fresh air is to open a window or door. However, the last thing most Las Vegas residents want is to let hot air into the house at the peak of summer.
For most people, the standard ventilation built into the HVAC system is sufficient to maintain a comfortable home. If, however, you are prone to allergies or the dry Nevada air causes frequent bouts of sinusitis, you can improve your home’s air quality by adding an air purifier or filtration system.
Want to Upgrade Your HVAC System?
While the traditional split system is still the most common HVAC system in use, there are other systems available, such as packaged units, ductless mini-split systems, and heat pumps. If you want to replace or upgrade your current HVAC system and are considering switching to a different type of heating and cooling system, call The Cooling Company at 702-567-0707. We’ll explain the different options available and help you choose the system that best suits your home.