Introduction
Heating, Ventilating and Air Conditioning, HVAC, is a huge field. HVAC systems include a range from the simplest hand-stoked stove, used for comfort heating, to the extremely reliable total air-conditioning systems found in sub- marines and space shuttles. Cooling equipment varies from the small domestic unit to refrigeration machines that are 10,000 times the size, which are used in industrial processes.
Depending on the complexity of the requirements, the HVAC designer must consider many more issues than simply keeping temperatures comfortable. This chapter will introduce you to the fundamental concepts that are used by designers to make decisions about system design, operation, and maintenance.
Brief History of HVAC
For millennia, people have used fire for heating. Initially, the air required to keep the fire going ensured adequate ventilation for the occupants. However, as central furnaces with piped steam or hot water became available for heat- ing, the need for separate ventilation became apparent. By the late 1880s, rules of thumb for ventilation design were developed and used in many countries.
In 1851 Dr. John Gorrie was granted U.S. patent 8080 for a refrigeration machine. By the 1880s, refrigeration became available for industrial purposes. Initially, the two main uses were freezing meat for transport and making ice. However, in the early 1900s there was a new initiative to keep buildings cool for comfort. Cooling the New York Stock Exchange, in 1902, was one of the first comfort cooling systems. Comfort cooling was called “air conditioning.” Our title, “HVAC,” thus captures the development of our industry. The term “air conditioning” has gradually changed, from meaning just cooling, to the
total control of:
Temperature
Moisture in the air (humidity)
Supply of outside air for ventilation
Filtration of airborne particles
Air movement in the occupied space
Throughout the rest of this text we will use the term “air conditioning” to include all of these issues and continue to use “HVAC” where only some of the elements of full air conditioning are being controlled.
To study the historical record of HVAC is to take a fascinating trip through the tremendous technical and scientific record of society. There are the pioneers such as Robert Boyle, Sadi Carnot, John Dalton, James Watt, Benjamin Franklin, John Gorrie, Lord Kelvin, Ferdinand Carré, Willis Carrier and Thomas Midgley, along with many others, who have brought us to our current state. Air-conditioning technology has developed since 1900 through the joint accomplishments of science and engineering. Advances in thermodynamics, fluid mechanics, electricity, electronics, construction, materials, medicine, controls and social behavior are the building blocks to better engineered products of air conditioning.
Historical accounts are not required as part of this course but, for the enjoyment and perspective it provides, it is worth reading an article such as “Milestones in Air Conditioning,” by Walter A. Grant1 or the book about Willis Carrier, The Father of Air Conditioning.2 The textbook Principles of Heating, Ventilating, and Air Conditioning,3 starts with a concise and comprehensive his- tory of the HVAC industry.
HVAC evolved based on:
Technological discoveries, such as refrigeration, that were quickly adopted for food storage.
Economic pressures, such as the reduction in ventilation rates after the 1973 energy crisis.
Computerization and networking, used for sophisticated control of large complex systems serving numerous buildings.
Medical discoveries, such as the effects of second hand smoke on people, which influenced ventilation methods.