Previously, we reviewed some salient fundamentals that are essential to understanding how things work in the HVAC/R industry, and why they work the way they do. Piggybacking off this topic, there are other rudimentary elements in play that are vital to conceptualizing the “how’s and why’s” as well; however, this topic is more focused on the “what” that makes things work. Specifically, we are addressing the basics of matter and energy.
Textually, matter is defined a substance that occupies space and has mass. It can generally be observed in one of three primary states: solid, liquid, or gas. Each of these states is bound to the laws of physics and thermodynamics as the heat content and pressure of the matter determines its state. It is important to note the distinction between mass and weight, as they are interrelated but not the same.
Mass is the property of matter that responds to gravitational attraction; weight, while not a property of matter, is also dependent on gravitational attraction. A substance’s density, or its mass-to-volume relationship, affects its specific gravity, in that it is calculated using the substance’s own density divided by the density of water. For example, since water has a density of 62.4 lb/ft³ at standard ambient temperature, its specific gravity is 1.0.
Mass is the property of matter that responds to gravitational attraction; weight, while not a property of matter, is also dependent on gravitational attraction. A substance’s density, or its mass-to-volume relationship, affects its specific gravity, in that it is calculated using the substance’s own density divided by the density of water. For example, since water has a density of 62.4 lb/ft³ at standard ambient temperature, its specific gravity is 1.0.
Specific volume, on the other hand, refers to volume that each pound of gas occupies. One related application would be to determine the horsepower (hp) needed in air conditioning work as it relates to choosing the correct size compressor or vapor pump needed for the task. Recall that 1 hp is equivalent to lifting 33,000 ft-lb/min and is used to express the rate at which work is performed; for example, a fan in the average furnace is rated as ½ hp.
Circling back to the previous discussion regarding how gasses respond to changes in pressure and temperature, there are three primary laws that come into play: Boyle’s Law, Charles’ Law, and Dalton’s Law. A fourth law, the General Law of Perfect Gas, is essentially a combination of the first two mentioned. Using the General Law of Perfect Gas, it is found that when temperature is constant P1 x V1 = P2 x V2 (Boyle’s Law); when pressure is constant, we find that V1/T1 = V2/T2 (Charles’ Law). Dalton’s Law works in synchronous conjunction with these other laws, as it stipulates that the total pressure of a confined mixture of gasses maintains equilibrium as the sum of the pressures each gas exerts individually.
These laws are immutable and one who understands these fundamental laws of nature will be able to build from this foundation a deeper understanding of most – if not all – heating and air-conditioning processes and applications. No matter what the application is, it requires the use of energy to complete the work. It is important to note the that purchase of energy, whether electrical or heat, plays its own integral role in this industry as it governs the proper operation of equipment used in gas furnaces, fossil-fuel power plants and the like. When energy is used as work, it is often described in terms of watts (W) and British thermal units (BTU) respectively. A quick reference for converting from heat energy to electrical is 3.413 BTU= 1 W. If you want to convert electrical energy to heat, it is read as 1 kW = 3413 BTU.
Now that we have covered the basic concepts utilized in the HVAC/R industry, be sure to join us next time as we discuss the fundamentals of refrigeration in action! If you would like to learn more, consider joining Team Cajun Air by clicking the link below! We are currently hiring and looking for qualified technicians that enjoy working in a high demand industry with great potential for growth professionally! Don’t delay, send in your resume TODAY!