At some point in the spring or early summer, uncomfortable temperatures force homeowners to make the switch from ‘heat’ to ‘cool’ on their thermostat. As the flowers bloom and warm sunshine raises the temperature, it’s the perfect time to share some basic facts about your air conditioning system, the science involved, and how it has impacted population growth.
TONS of Cooling and a Match!
As a kid, you may have learned that one ton is equal to 2,000 pounds. Based on that knowledge, if you have a 4-ton air conditioner, you would expect the equipment to weigh 8,000 pounds. That would be almost twice the weight of a mid-sized SUV! The good news is that the tonnage or weight assigned to air conditioners has nothing to do with the weight of the equipment but with the historical fact that people used to cool spaces with blocks of ice.
Before modern cooling systems, people rated the capacity to cool indoor spaces by melted ice. For ice to melt, heat is transferred from its surroundings to the ice - causing it to melt. It takes 143 British Thermal Units (BTUs) to melt one pound of ice. To melt one “ton” of ice, you need approximately 12,000BTUs/hr. Do you see the ice/air conditioner connection yet?
To make things even more interesting, one BTU equals the amount of heat you get from burning one kitchen match all the way down to the end. So the actual size of your air conditioner or heat pump is a combination of BTUs and tons!
One ton = the ability to cool 12,000 BTUs in an hour
Your professional licensed HVAC contractor uses specific calculations to determine the correct “ton” air conditioner required to cool your home efficiently. It’s essential that a properly sized, specifically matched unit be installed in your specific home. And thanks to technological advancements, the ‘tons’ of cooling have nothing to do with massive blocks of ice.
Physics Can be Really Cool!
Like many technological advancements, you can thank physics for helping you stay cool in your home. Air conditioners use the basic laws of physics and the refrigeration cycle to maintain a comfortable indoor temperature when the outdoors heat up. When liquid changes into a gas, it extracts or pulls heat from its surroundings. You can test out this basic concept for yourself with a water faucet and your hand!
- Put your hand in warm water and then hold it up in the air.
- The wet hand will feel cooler than the dry hand, especially if there is some air movement.
- Why? Because the water is evaporating!
- As the water evaporates, it pulls heat away from your hand.
Cooling with the Refrigeration Cycle
The principles of physics are used in the refrigeration cycle. This cycle removes heat from one area and distributes it to another. With induced pressure changes from the condenser coil, compressor, evaporator coil and the expansion valve, the state of the refrigerant is forced to fluctuate between a liquid and gas - and as you now know, when liquid changes into a gas, it extracts or pulls heat from its surroundings. This continuous cycle allows the heat to be transferred from inside your home to the exterior.
Here’s how it works:1
- The refrigerant comes into the compressor as a low-pressure gas. It is then compressed” to become a high-pressure gas.
- The gas then flows through the condenser coil. Here the gas “condenses” to a liquid, and gives off its heat to the outside air.
- The liquid then moves to the expansion valve under high pressure. This valve restricts the flow of the fluid and lowers its pressure as it leaves the expansion valve.
- The low-pressure liquid then moves to the evaporator coil, where heat from the inside air is absorbed and changes it from a liquid to a gas.
- As a hot low-pressure gas, the refrigerant moves to the compressor where the entire cycle is repeated.
Heat and Humidity!
Believe it or not, there is water all around us - even when it’s not raining! Humidity is the amount of water vapor in the air. Air with higher humidity has an increased amount of water vapor.
When the humidity level is high, especially when combined with high temperatures, you may be uncomfortable! That’s because sweat may not evaporate as quickly as it would with a lower humidity level. This phenomenon may make us feel hotter than the actual temperature because evaporation is slowed.
If you think about the wet hand experiment - if the humidity level is high, it may take longer for the air to absorb the extra moisture on your wet hand. That means that your hand wouldn’t feel as cold because evaporation is slowed. This explains why it feels hotter when the humidity levels are high. Likewise, very low humidity can make us feel colder than the actual temperature. This happens because the dry air helps moisture evaporate more quickly than usual.
So how can an air conditioning help you feel more comfortable in your home? When warm air comes in contact with your air conditioner’s or heat pump’s cold evaporator coil, some moisture may be condensed out of the air, making your home feel less humid. The moisture collected by the evaporator coil goes to a drain and then it is sent outside, away from your home. But air conditioners and heat pumps are not meant to control indoor humidity; it just happens to be an incidental byproduct of the refrigeration cycle!
Indoor Comfort and Population Growth
If you have ever come inside a cool home on a hot day, you can understand why air conditioning is continuously named as one of the top inventions in modern history. Most warm-weather states can thank the air conditioner for their increasing populations. Can you imagine what life must have been like during those southern summer days before air conditioning?
As air conditioning became more affordable, its popularity grew. By the 1950s, more than one million room air conditioning units had been sold. However, it wasn’t until 1977 that newly constructed homes tipped the scales of residential air conditioning. In 1977, 54% of newly constructed single-family homes had air conditioning compared to the 46% that weren’t built with air conditioning.2 The upward trend has continued for decades.
By 2015, the U.S. Census revealed that nearly 93% of newly constructed homes in the United States were built with air conditioning. However, the numbers also acknowledged that between 1997 and 2015, over 99% of newly constructed homes in the “south” were built with air conditioning.2 It appears that cool, indoor comfort is a priority. Whether for personal or economic reasons, air conditioning will continue to advance and thrive!
1 Southwest Wisconsin Technical College. Basic Refrigeration Cycle. n.d. https://www.swtc.edu/Ag_Power/air_conditioning/lecture/basic_cycle.htm. 7 April 2017.
2 U.S. Census Bureau. "Presence of Air-Conditioning in New Single-Family Houses Completed." U.S. Census Bureau - Air Conditioning. Washington D.C.: U.S. Department of Commerce, 2015. 1-20. https://www.census.gov/construction/chars/pdf/aircond.pdf.