Kilocalorie (IT) per Hour per Square Meter [kcal(IT)/(h·m²)]

The unit kilocalorie (IT) per hour per square meter, written as kcal(IT)/(h·m²), measures heat flux density or thermal power per unit area using the International Table kilocalorie (1 kcal(IT) = 4186.8 J). It represents the amount of heat energy transferred through 1 square meter of surface in 1 hour.

This unit is often used in building engineering, HVAC, and solar energy studies to quantify energy transfer through walls, roofs, or solar collectors. Typical applications include:

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  Heat gain or loss through building surfaces

  
  
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  Solar energy incident on rooftops or flat surfaces

  
  
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  Design of heating and cooling systems

  
  

Mathematically, heat flux is expressed as:

where q is heat flux in kcal(IT)/(h·m²), Q is total heat in kilocalories, A is area in m², and t is time in hours.

Conversion to SI units:

Although SI units such as W/m² are now standard, kcal(IT)/(h·m²) remains useful in legacy building and thermal engineering literature, providing an intuitive measure of energy transfer over time in kilocalories.

Horsepower per Square Foot [hp/ft²]

The unit horsepower per square foot, written as hp/ft², measures power or energy flux density per unit area in the Imperial system. One horsepower (hp) is defined as 745.7 watts, representing the rate of doing work or energy transfer. Dividing by square feet gives the amount of power delivered or absorbed per unit area.

This unit is used in engineering, HVAC, and industrial applications to describe concentrated power distribution. Typical uses include:

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  Power output of engines or motors per area of a platform

  
  
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  Mechanical energy flux in manufacturing equipment

  
  
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  Evaluation of energy delivery systems on surfaces or panels

  
  

Mathematically, power flux can be expressed as:

where q is power per unit area (hp/ft²), P is power in horsepower, and A is area in ft².

Conversion to SI units:

Although W/m² is the SI standard, hp/ft² is convenient in U.S.-based applications and historical literature, providing an intuitive measure of high power density over a surface in familiar Imperial units.