How to Heat 100 Gallons of Liquid

The power required to heat water can be calculated.

A very common industrial process operation is heating liquids. Process design engineers need to calculate power requirements to heat certain liquids from one temperature to another. The determination of how much power is required is a simple calculation that considers the mass of the liquid, the liquid's specific heat capacity (how much energy is required to heat one pound of liquid one degree), the desired temperature change (final temperature minus starting temperature) and how long is required for heat up.

Things You'll Need

• Pen
• Paper
• Calculator

Instructions

1. Determine the liquid to be heated, temperature change and time to reach final temperature. Assume 100 gallons of water at ambient temperature (70 degrees Fahrenheit) is to be heated to 150 degrees Fahrenheit within 30 minutes.

2. Calculate the mass of the water using water's density, which is 8.33 pounds per gallon. This is done by multiplying density by volume or 8.33 x 100 for a mass of 833 pounds of water.

3. Determine the wattage (power) required to heat 100 gallons of water from 70 degrees to 150 degrees in 30 minutes. This is done using the formula W=m x h x "T/(3.412 x t), where W is the wattage required, m is the mass of the liquid (pounds), h is the specific heat of the liquid (BTU/lb °F), "T is the temperature change, 3.412 is a conversion factor (BTU to watt/hr) and t is the heat up time in hours. Plugging in the values yields an expression of W = 833 pounds x 1.0 BTU/lb °F x 80/(3.412 x 0.5) for an answer of 39,062 watts or about 39 kilowatts. Therefore, if 39 kilowatts of power is applied to 100 gallons of water for 30 minutes, the final temperature will reach 150 degrees.

References

• NPH Heaters: Heat Calculation Examples
• Riviera Utilities: Hot Water Usage