Cool Concept

by Katie Lee

How air conditioning created a world that relies on keeping people comfortable — and keeping businesses running.

By John Haley

How far back in time do you need to go to know when the concept of “air conditioning” was conceived? Fifty years? A hundred? Could it be more? The actual answer is thousands! It is said that the ancient Egyptians developed and practiced the concept of air conditioning. In an attempt to find relief from the heat, reeds were hung from windows and a small constant stream of water trickled down the reeds. As the water evaporated on the reeds, it cooled the air blowing through the window, lowering the temperature and providing a more comfortable environment. Although this process seems extremely basic, throughout history the general physics of air conditioning has remained the same.

In the early 1900s an engineering student by the name of Willis Carrier graduated from Cornell University and found himself working to find a way to solve an application problem for a publishing company in Brooklyn, New York. This company was experiencing many setbacks, as high humidity levels created a challenge with maintaining the printing paper which was the life blood of the business. Willis used his knowledge of heat transfer and simply tried to reverse the process. Hence the first modern electric air conditioner was invented. Instead of sending air through hot coils to create warm air, he sent air through cold coils, which cooled the air and reduced the moisture content in the space. This process helped maintain proper ink alignment and paper dimensions, making it a break-through in the printing industry. It was this technology that was later used to increase productivity in the workplace, and eventually improve comfort in homes.

As we fast-forward to 2014, the process by which air conditioners work is still based on Carrier’s very simple scientific principle. But the application of a few clever mechanical techniques have changed the footprint and made large-scale cooling not only possible, but a necessity in the commercial world. Newer technology means many more moving parts, which then creates the need for a maintenance program to ensure proper functionality.

Before we talk about the importance of maintaining these systems, let’s take a look at how an air conditioning system really works.

HVACAir conditioners operate by taking advantage of a physical law called ‘phase conversion.’ This process is the absorption of heat when a liquid converts to a gas. Phase conversion is exploited by air conditioners by forcing chemical compounds — in this case, refrigerant — to evaporate and condense over and over again in a closed system. The refrigerants are passed through internal evaporator coils and external condenser coils, and through this cycle, the air is cooled.

The indoor blower system is a critical part of an air conditioning system and is responsible for constantly moving the inside air. When the warm air passes over the cold, low pressure evaporator coils, the refrigerant inside absorbs the heat as it changes from a liquid to a gas. This process starts to lower the humidity and the temperature of the air. In order to keep cooling efficiently, the air conditioner has to constantly convert the refrigerant back to a liquid. To accomplish this, a compressor puts the gas under high pressure which creates unwanted heat. The unwanted heat is then pushed to another set of coils, called condenser coils, located in the outdoor unit. A second fan pushes air across the condenser coils to help cool down the high pressure gas. As the gas cools, it changes back to a liquid and the process starts all over again. This cycle is endless and continues to bring down the temperature of the air until the thermostat is satisfied.

Although the creation of air conditioning seems like a cycle that will continue without fail, maintenance is mandatory in order to keep the phase conversion working properly. In the refrigeration cycle there are two critical areas, which allow for the heat to be absorbed and exhausted or, in other words, exchanged. This heat exchange happens in the indoor evaporator coil and the outside condenser coil. When the system is new it operates very efficiently, as both coils are clean, which allows for exceptional heat transfer. But what happens when systems aren’t maintained and the coils collect dirt? Several things…

Let’s start inside the space and talk about the evaporator coils. As the system constantly pulls air in and pushes air through the evaporator coils, dirt and dust will make its way into the air stream. Most of this debris will be caught by the filters. But when filters become clogged the debris can hit the coils. When the evaporator coils start to become coated in dirt, the heat exchange process starts to suffer, and the cooling output starts to decrease, forcing the unit to run longer to maintain the temperature. This increase in run time will result in higher energy consumption.

filter changeThe filters can also directly affect the system. As filters catch debris they start to increase in density, which in turn requires more force to push air through. There comes a point when the force of the fan cannot overcome the density of the filter and this creates a lack of airflow across the evaporator coil, which also affects the heat exchange process. Instead of the cold liquid-filled evaporator coil absorbing the heat and turning the liquid into gas, a percentage of the liquid does not change to gas and continues to get colder. Over time this will result in the coil freezing, which will lead to a system shutdown.

On the outside there is a second set of coils known as the condenser coils. We don’t have the luxury of filters to protect the condenser coils, so dirt buildup is inevitable. The amount of buildup on the condenser coils will differ based on the conditions of the surrounding areas. Condenser coils located near a highway will collect dirt faster than those near an area with little movement. Regardless of the location, the coils should be cleaned routinely in order to keep the air conditioning system running properly. When the condenser coils are coated with dirt the heat exchange process is affected and the system will experience longer run times and possibly even breakdowns.

In review, the common thought here is the importance of keeping both the evaporator and condenser coils clean as phase conversion is the lifeblood of any air conditioning system. Absorbing heat from the space and exhausting it outside over and over again will keep your building cool and comfortable. But when the evaporator and condenser coils start to experience buildup of dirt and debris, the entire refrigeration cycle is affected, which will ultimately lead to a system breakdown and an uncomfortable environment.

As a business owner or facilities manager, keeping your air conditioning systems operating should be just as important as keeping the lights on. Regardless of what type of business you are in, one of the easiest ways to keep your air conditioning systems running properly is to develop a maintenance program. A program that consists of regularly scheduled filter changes and coil cleanings will not only keep your systems running properly, it will help you manage your energy consumption — which, at the end of the day, will reduce your operating costs.

When Willis Carrier invented the very simple process of air conditioning in the early 1900s I’m sure he had no idea it would completely revolutionize how people live. It eventually created a world that relies on keeping people comfortable — and keeping businesses running.

Pretty cool idea, Mr. Carrier.

— John Haley is the director of HVAC programs for Ferrandino & Son. He has over 25 years of management, operational and technical expertise. The author may be reached at [email protected].

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