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How to Calculate Heat from a VDC

A VDC is a variable frequency direct current drive controller for a motor or other electrical component. A VDC works by manipulating the voltage supply to the electrical component. In doing so, the heat output provided by a VDC-controlled device also is variable. The calculation to convert power in horsepower to heat -- British thermal units -- is straightforward.

Things You'll Need

Pen
Paper
Calculator

Instructions

- 1
  Determine the maximum horsepower of a motor and the supply voltage variability of the VDC. VDCs can control the voltage to a device in linear increments and can be as precise as fractions of maximum voltage up to larger steps. For instance, if the motor has a maximum rating of 100 horsepower at 220 volts and the VDC controls the voltage in 1/4 increments, then the corresponding horsepower to voltage is linear. This is 25 percent, 50 percent, 75 percent and 100 percent of 220 volts with corresponding horsepowers of 25, 50, 75 and 100.
- 2
  Convert the units of horsepower into BTUs. One BTU is defined as the energy required to raise 1 pound of water by 1 degree Fahrenheit in temperature. The conversion is 33,472 BTUs per 1 horsepower. Once you know the horsepower at each voltage, simply multiply that value by 33,472 to convert into BTUs.
- 3
  Calculate the heat generated by using the VDC on the motor at the four different settings. The calculations are 25 horsepower times 33,472 equals 836,800 BTU, 50 horsepower times 33,472 equals 1,673,600 BTU, 75 horsepower times 33,472 equals 2,510,400 BTU and 100 horsepower times 33,472 equals 3,347,200 BTU.

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