Want to Know How Your AC works?

Published on: July 31, 2012

Air conditioning is a great modern convenience and an impressive technology. A rare and expensive luxury at the beginning of the twentieth century, air conditioning systems are now a standard feature of homes and commercial buildings all over the U.S.

Although radiant cooling systems exist, most air conditioners in use today are evaporative systems. In older homes and buildings that were not originally air conditioned, window or wall-mounted all-in-one systems are popular. Split systems that are part of a forced air HVAC system are the most common source of cooling in newer buildings.

All-in-one units and split systems work in basically the same way. They are divided into a condenser section or unit, and an evaporator section or unit. In a split system, the evaporator is indoors and the condenser is outdoors. In a window or wall unit, the evaporator is on the inside and the condenser is on the outside.

Air conditioning system basics

In a split system, a refrigerant is circulated between the evaporator and the condenser in insulated pipes. When it’s inside, it absorbs heat from the air that’s being circulated through the building. When it’s outside, it releases that heat into the atmosphere. All-in-one units are installed through windows or walls, and the refrigerant simply circulates within the air conditioner. The genius of these systems is that they’re able to take heat from a cooler area and release it into a hotter area.

Below is a diagram of an all-in-one air conditioner. Notice the division between the inside and outside half of the unit.

By Pbroks13 [CC-BY-3.0], via Wikimedia Commons

In a split system, those functions would be separated into two units. The indoor unit, or evaporator, would be part of the air handler. The air handler would contain both the air conditioning evaporator and a blower to distribute both heated and cooled air to the vents. Air handlers are usually part of an integrated forced air HVAC system that also includes a furnace.

In contrast, an all-in-one air conditioning unit operates independently of the rest of the HVAC system. That’s why they are often used in homes and commercial buildings with dedicated radiant heating systems.

How the condenser works

The condenser is located at the building exterior.

The refrigerant comes into the condenser as a gas. It’s fairly cool and at a low pressure, because the heat from the interior has just boiled it and forced it to evaporate.

The compressor turns that cool, low pressure gas into a hot, high pressure gas of approximately 150° F. Then, the refrigerant gas passes through the condensing coil, and a fan blows the outside air over it in order to cool it. Even though the outside air is hot, it isn’t as hot as the refrigerant. The refrigerant releases the heat that’s keeping it in the form of a gas. It becomes a hot, high pressure liquid, and it travels back to the evaporator.

The fact the hot outdoor air is used to cool the even hotter refrigerant can backfire when it’s too warm outside. As the temperature gets higher, the air conditioning can start to become less effective.

It’s also very important to keep the condenser coil in good repair and clear of any interference. If the fins are crushed or if there’s vegetation blocking the outdoor unit, it will have trouble cooling the refrigerant properly, and it will run less effectively and less efficiently.

How the evaporator works

The evaporator is located in the building interior.

The refrigerant comes into the evaporator as a hot, high temperature liquid of approximately 100° F. It then goes through an expansion device that turns it into a cool, low pressure liquid. Its temperature reduces from approximately 100° F to around 20° F. Then, a fan blows the household air across the cool refrigerant in the evaporator coil. This causes the refrigerant to absorb the heat from the air. It boils, evaporates, and becomes a cool, low pressure gas. At that point, it is sent back to the condenser unit.

Understanding how your HVAC system works can help you to make wise and confident decisions about repairs and replacements, and it can also help you understand how to keep the units you already own operating at peak efficiency. HVAC systems are often responsible for 50% or more of total building energy use, so keeping the air conditioning running smoothly is vital for controlling energy costs.