# Temperature of Refrigeration

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## Temperature of Refrigeration

Temperature can be thought of as a description of the level ofĀ heat and also may be referred to as heat intensity. Heat levelĀ and heat intensity should not be confused with the amountĀ of heat, or heat content. As a substance receives more heat,Ā its molecular motion, and therefore its temperature, increases.

Most people know that the freezing point of water isĀ 32 degrees Fahrenheit (32Ā°F) and that the boiling point is
212 degrees Fahrenheit (212Ā°F), Figure 1. These pointsĀ are commonly indicated on a thermometer, which is an
instrument that measures temperature.

We must clarify the statements that water boils at 212Ā°FĀ and freezes at 32Ā°F. These temperatures are accurate when
standard atmospheric conditions exist. Standard conditionsĀ occur at sea level with the barometer reading 29.92 in. HgĀ (14.696 psia); this topic is covered in detail later in thisĀ section in the discussion of pressure. It is importantĀ to understand the concept of standard conditions becauseĀ these are the conditions that will be applied to actual practiceĀ later in this book.

Heat theory states that the lowest attainable temperatureĀ is 460Ā°F. This is the temperature at which allĀ molecular motion stops and the temperature at whichĀ there is no heat present. This is a theoretical temperatureĀ because molecular motion has never been totally stopped.Ā The complete stopping of molecular motion is expressedĀ as absolute zero, calculated to be 460Ā°F. Scientists haveĀ actually come very close to reaching this point in a laboratory
by dropping the temperature to within one-millionthĀ of a degree of absolute zero.

The Fahrenheit temperature scale is part of the EnglishĀ measurement system used by the United States. This measurementĀ system is also known as the I-P, or inch-pound,Ā system. The Celsius temperature scale is used in the InternationalĀ System of Units (SI) or metric system used by mostĀ other countries. Some important Fahrenheit and CelsiusĀ equivalent temperatures are provided in Figure 2. See theĀ Temperature Conversion Table in the appendix of this textĀ for more temperature conversions.

Hereās how to use the Temperature Conversion chart.Ā To convert a room temperature of 78Ā°F to degrees Celsius,Ā move down the column labeled āTemperature to BeĀ Convertedā until you fi nd 78. Look to the right under theĀ column marked āĀ°C,ā and you will fi nd 25.6Ā°C. To convertĀ 36Ā°C to degrees Fahrenheit, look down the column labeledĀ āTemperature to Be Convertedā until you fi nd 36. Look toĀ the left and you will fi nd 96.8Ā°F. Formulas can also be usedĀ to make conversions.Ā If we have a Celsius temperature that we want to convertĀ to a Fahrenheit temperature, we can use the followingĀ formula:

Ā°F = (1.8 * Ā°C) +Ā 32Ā°

For example, if we had a Celsius temperature of 20Ā°C, weĀ can determine the equivalent Fahrenheit temperature by
plugging the Celsius value into the formula to get:

Ā°F = (1.8 * Ā°C) + 32Ā°

Ā°F = (1.8 * 20Ā°C) + 32Ā°

Ā°F = 36Ā° + 32Ā°

Ā°F = 68Ā°

So, 20Ā°C = 68Ā°F

If we have a Fahrenheit temperature that we want toĀ convert to a Celsius temperature, we can use the followingĀ formula:

Ā°C = (Ā°F – 32Ā°) / 1.8

For example, if we had a Fahrenheit temperature of 50Ā°F,Ā we can determine the equivalent Celsius temperature by
plugging the Fahrenheit value into the formula to get:

Ā°C = (Ā°F – 32Ā°) / 1.8

Ā°C = (50Ā°F – 32Ā°) / 1.8

Ā°C = 18Ā° / 1.8

Ā°C = 10Ā°

So, 50Ā°F = 10Ā°C

Up to this point, temperature has been expressed inĀ everyday terms. It is equally important in the HVAC/RĀ industry to refer to temperature in engineering and scientific terms. Performance ratings of equipment are establishedĀ using absolute temperatures. Performance ratingsĀ allow for easy comparison among equipment producedĀ by different manufacturers. The Fahrenheit absoluteĀ scale is called the Rankine scale (named for its inventor,Ā W. J. M. Rankine), and the Celsius absolute scale is knownĀ as the Kelvin scale (named for the scientist Lord Kelvin).Ā Absolute temperature scales begin where molecular motionĀ starts; and use 0 as the starting point. For instance,Ā 0 on the Fahrenheit absolute scale is called absolute zeroĀ or 0Ā° Rankine (0Ā°R). Similarly, 0 on the Celsius absoluteĀ scale is called absolute zero or 0 Kelvin (0Ā°K), Figure 3.Ā The Fahrenheit/Celsius and the Rankine/Kelvin scales areĀ used interchangeably to describe equipment and fundamentalsĀ of this industry.

Copied fromĀ REFRIGERATION &Ā AIR CONDITIONINGĀ TECHNOLOGY byĀ WILLIAM C. WHITMAN,Ā WILLIAM M. JOHNSON,Ā JOHN A. TOMCZYK andĀ EUGENE SILBERSTEIN

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