Lecture notes 6 - Sizing Residential AIR Conditioning Systems RULE-OF- Thumb Methods PDF

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Heating Ventilation and Air Conditioning System...

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SIZING RESIDENTIAL AIR CONDITIONING SYSTEMS RULE-OF-THUMB METHODS The most common rule of thumb is to use 500 square feet per ton to determine the size of air conditioner needed. Or 400 or 600 or some other number in that general vicinity. 1 

Upgrade Method Indoor air quality is one of the top five health concerns, according to the Environmental Protection Agency. Lung-related reactions such as asthma and allergies are less likely when indoor air is cleaner. Low-speed fans on a modern, improved AC unit might help to improve air circulation and clear the air in your house. When it comes to updating your air conditioner, one of the most important considerations is the cooling capacity. It's not a good idea to estimate your cooling power demands based on your previous air conditioner because of advancements in energy efficiency. Instead, you must consider the amount of windows in your home, as well as the architecture and size of the structure. The amount of shade your home receives, the position of registers, and the room orientation are all elements to consider.

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Square footage Methods Determine square footage: Find out the floor space in your home. You might be able to find the number written down somewhere, or you might have to measure it yourself. To measure a room on your own, use a tape measure to determine the length and width. Multiply those together for the square footage for that room. Repeat the process for each room and hallway, then add them all together2. To calculate the size, simply multiply the length times the width of the room or area to be cooled. Then, as a practical number, multiply that total times 25 BTU. This allows ample cooling, whether it is a rainy, moist day or a hot, sunny, humid day. Let’s say the room is 12 feet wide by 15 feet long. That means 12x15=180 square feet. Take the 180 sq. ft. times 25 BTU per square foot and you get the minimum BTU air conditioner you should buy. That means 180x25=4500 BTU cooling capacity is needed. You may ask yourself: will a smaller air conditioner work or will a larger one be better? Here’s a thought about those questions. Smaller BTU units will continually run, just to try to keep up. This will increase your electric bill and it is unlikely the unit will be able to cool the area effectively.

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Chart Method

1 https://www.energyvanguard.com/blog/more-on-air-conditioner-sizing-rules-of-thumb/#:~:text=The%20most %20common%20rule%20of,number%20in%20that%20general%20vicinity. 2 https://theclimatetech.com/how-to-determine-the-size-of-hvac-you-need/

The chart below is a great starting point for sizing your AC. These BTU calculations are based on a standard room with 8-foot ceilings, two windows and one door. If the room has more windows, doors or higher ceilings, adjust the BTUs upward. Other factors in determining the BTU size would be the room’s purpose. Kitchens normally have more heat thanks to stoves and ovens, and rooms with computers and other electronics give off extra heat. Therefore, these rooms would require bumping the air conditioner size up....