Sizing Portable Air Conditioners

Air conditioners are sized according to British Thermal Units, or BTU per hour. A BTU is a basic measurement of heat energy that refers to the amount of heat necessary to raise the temperature of one pound of water by one degree Fahrenheit. Without any environmental concerns, approximately 20 BTU will cool 1 square foot. So, the first step in sizing a portable air conditioner to meet your needs is to calculate the BTU needed, based on the square footage of the area to be cooled.

Square Footage

To calculate the square footage for the room that needs portable cooling, you must use the appropriate formula for the shape of your room.

  • Rectangle & Square Shaped Rooms
    • Multiply the length of the room by the width of the room. For example, if your room is 10 foot by 12 foot then, 10 x 12 = 120 sqf.
  • Triangle Shaped Rooms
    • Multiply the length (height) by the width (base) and divide by 2. For example, if the triangle has a base of 15 feet and a height of 35 then, 35 x 15 / 2 = 262.5 sqf.
  • Circular Rooms
    • Multiply the distance from the center of your room to the wall (radius) by itself and then by 3.14. For example, if your room has a radius of 12 then, (12 x 12) x 3.14 = 452.16 sqf.

Once the square footage is determined, it needs to be multiplied by 20 BTU per square foot. So, in our examples above, the rectangle room would require at least 2,400 BTU; the triangle would need 5,250 BTU; and the circular room would need 9,043 BTU.

Environmental Concerns

In addition to BTU requirements, there are many important factors to consider when selecting a portable air conditioner for your cooling application.

  • Ambient Temperatures - What is the temperature surrounding the unit? Each portable air conditioner has a different temperature range for optimal performance. Some units won't work well above 100°F, for example.
  • Power Type - What forms of electrical power are available? The availability of electrical power is regularly a leading factor in unit selection. For example, in an application requiring three tons of cooling, a 3-ton unit may be the reasonable choice. However, a 3-ton portable air conditioner requires a 208-230 volt, single phase, 30-amp circuit. The same 3-tons of cooling can be achieved by using two 1.5-ton units, which can be operated from a standard plug.
  • Location - Will the air conditioner be placed inside or out of the space being cooled?
  • BTU Needed - What is the total required cooling load expressed in BTU or cooling tons?
  • Environment - Is air pressure a concern in the building?
  • Cooling Preference - Is it easier to provide a water source and drain, or to vent exhaust from the unit?
  • Exhaust Method - Will the hot exhaust be vented into the existing duct system or will the units blow freely into the space surrounding them?
  • Space - Are there any physical restrictions in your desired space?
  • Drainage - Do you have availability to drain the unit of condensation, or will a tank have to be used and emptied?

These are all crucial factors in determining if you need a small, large, water-cooled, or air-cooled unit. Let Mobile Air’s expertise in cooling applications benefit you. Contact us at Mobile air and we will determine the best solution for your HVAC problem.

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