CHU/Hour/Square Foot

The unit CHU/hour/square foot is used to measure Cooling Heat Units per hour per square foot, commonly applied in air conditioning and refrigeration calculations. It indicates the amount of cooling energy, in CHUs, that passes through or is required for one square foot of a surface area over an hour. This measurement helps engineers and designers assess cooling loads, select appropriate air conditioning systems, and ensure thermal comfort in buildings. A higher CHU/hour/square foot value shows greater heat gain, meaning more cooling is needed, while a lower value indicates better insulation or lower cooling requirements. It is essential in designing energy-efficient HVAC systems and optimizing equipment sizing, helping reduce operational costs and maintain desired indoor temperatures. By using CHU/hour/square foot calculations, building designers can balance comfort, energy efficiency, and sustainability effectively.

Btu (th) per Second per Square Inch [Btu(th)/(s·in²)]

The unit Btu (th) per second per square inch, written as Btu(th)/(s·in²), measures heat flux density or thermal power per unit area using the thermochemical British Thermal Unit (1 Btu(th) = 1054.35 J). It represents the amount of heat energy transferred through 1 square inch of surface every second.

This unit is commonly used in high-intensity thermal applications, engineering experiments, and solar energy studies where energy flux over small surfaces is significant. Typical applications include:

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  Heat flux from industrial furnaces or radiative heaters

  
  
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  Solar radiation on concentrated panels or small surfaces

  
  
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  Thermal testing of materials under high-intensity conditions

  
  

Heat flux can be expressed mathematically as:

where q is heat flux in Btu(th)/(s·in²), Q is energy in Btu(th), A is area in in², and t is time in seconds.

Conversion to SI units:

While SI units like W/m² are standard, Btu(th)/(s·in²) is useful in U.S. engineering, laboratory experiments, and historical references, providing an intuitive measure of high-intensity heat flux per square inch per second.