HVAC Fundamentals #1: What is HVAC
- Brendan Nelson, PE
- Jul 7
- 5 min read
For thousands of years, humanity has shaped the world around us, creating environments that are safer, healthier, and more comfortable for ourselves and for those who come after us. Modern HVAC systems are the culmination of centuries of engineering, craftsmanship, and innovation. Yet most people rarely notice the science quietly working around them - until it doesn't.
In this ten-part series, I'll pull back the curtain on the often-overlooked world of HVAC, exploring the principles behind airflow, ductwork, refrigeration, system design, construction, and commissioning. Whether you're just beginning your career or looking to strengthen your fundamentals, this series is intended to provide a solid foundation in one of the most important aspects of the built environment: the spaces we inhabit and the air we breathe.
So, what is the history of HVAC? Some of the earliest known heating systems, other than open fires, were known as hypocausts. Roman buildings were built on columns, creating a cavity where hot combustion gases circulated under the floor before exiting through terracotta flues in the walls, thus warming the floor and surrounding spaces. Public baths, wealthy homes, and palaces were heated like this beginning around the 1st century BC. Cooling systems also had some ancient roots, with ancient Egyptians hanging wet reeds or mats in windows or doorways, utilizing evaporative cooling as air passed over the water.
In 1556, German metallurgist Georgius Agricola wrote a book titled De Re Metallica, in which he detailed multiple ways to ventilate mine shafts. These included complicated wheel and pulley systems with feathers tied to them, serving as rudimentary fans. For deeper or larger mines, he details bellows connected to wooden pipes, either powered by man, horse, or water wheel, that compressed air and blew it deep into the mine to deliver breathable air to the workers. Images detailed in the book are shown below.
By the 1800's, buildings were primarily ventilated via the stack effect, or using the natural pressure differences in tall shafts to move air in the building. With more industrialization, working indoors, and office buildings, the need for ventilation air grew. Elsewhere, in 1836, French engineer and chemist Stanislas Sorel took out the first patents for a process of cleaning and coating steel by dipping it in zinc, called galvanizing. Modern duct's would later utilize this technology creating longer lasting, metal ductwork with better anti-corrosion properties.
In 1851, Dr. John Gorrie was a medical doctor in Apalachicola, Florida. He studied tropical diseases, particularly yellow fever. Yellow fever is transmitted by infected mosquitos, but that wouldn't be known for sometime after Dr. Gorrie's time. What physicians did observe, however, were the dangerously high fevers associated with the disease. In an attempt to combat these high temps, Dr. Gorrie would invent and patent a machine that allowed "the artificial production of ice" as stated in his patent no. 8080. This invention would lead him to be named the Father of Refrigeration.
What seems today like an obvious, society-changing invention, was viewed very differently at the time. The ice trade was an enormous industry in 1851, with certain industrialists making fortunes from the distribution and sale of ice. Boston alone exported almost 75,000 tons of ice in 1847 (reference below). The ice industry attempted to discredit him but by the end of the civil war, artificial ice production in the south was here to stay, along with a technology that would go on to reshape indoor air and comfort.
In 1902, Willis Carrier, a fresh Cornell University engineering graduate, was working at Sackett-Wilhelms Lithographing & Publishing Company in Brooklyn, NY. He was tasked with solving one problem, high humidity. It was causing paper to warp and affecting the print quality. He designed and patented a system of having air flow over cooling coils that could pull moisture from the air, thus drying the air. He solved the problem and in 1906 would go on to patent his process. This breakthrough would take refrigeration into the HVAC world and make Carrier the father of modern air conditioning. In 1915 he would co-found the Carrier Engineering Corporation, which today is still a leader in the field of HVAC. Just 2 years after this breakthrough, the American Society of Refrigerating Engineers (ASRE) was established.
In 1894, the American Society of Heating and Ventilating Engineers (ASH&VE) had its first meeting to discuss metal vs wood ductwork. In 1922, ASH&VE posted its first Heating and Ventilation guide, with the below stated purpose:
"The purpose of this new addition to the Society's publication is to provide the engineer, the architect and contractor alike, with a useful and reliable reference data book relating to the art of heating and ventilating. A wide range of data within the scope of the field is presented and every effort has been made to present the material in a practical and useful manner."
ASH&VE later became the American Society of Heating and Air-Conditioning Engineers (ASHAE) with the merger to the ASRE in 1959. The newly combined society combined ASHAE's The Guide and ASRE Refrigerating Data Book, into a combined publication called ASHRAE Guide and Data Book. This publication was later regrouped into ASHRAE's Handbook of Fundamentals. Separate publications of this book are still made regularly for Fundamentals, Equipment, and Applications all being separate books.
Today, the innovations are too numerous to mention: geothermal heating/cooling, heat pumps, data center cooling, variable refrigerant flow (VRF), advanced automation, passive heating, energy recovery, dedicated outdoor air systems, and countless others - all of which we'll explore throughout this series.
As one can see, there is no direct path or single breakthrough that caused the world of heating, cooling, and indoor comfort to be where it is today. Rather, it is a series of individual breakthrough moments, from heating bathhouses, to needing ventilation air in mines to keep working, to attempting to cool patients suffering from yellow fever, to solving printing issues, the path of innovation is anything but straight. Nevertheless, here we are, each technology building on the last, improving lives, allowing food to be safely stored and transported, providing clean, breathable air to inhabitants of buildings, keeping life saving vaccines stable, and much more, no one breakthrough possible without the last. Some smart guy had a quote one time that summarized this perfectly:
"If I have seen further, it is by standing on the shoulders of giants." - Sir Isaac Newton
Have a good day, and stay curious.
-BN
References & Further Reading
Georgius Agricola. De Re Metallica (1556). Internet Archive.
https://archive.org/details/deremetallica50agri/page/6/mode/2up
John Gorrie. Improvement in the Process for the Artificial Production of Ice. U.S. Patent No. 8,080 (1851).
Boston University. Tracing the History of the New England Ice Trade.
https://www.bu.edu/articles/2022/tracing-the-history-of-new-england-ice-trade/
American Society of Heating, Refrigerating and Air-Conditioning Engineers. A Brief History of the ASHRAE Handbook.
Willis Carrier. Apparatus for Treating Air. U.S. Patent No. 808,897 (1906).
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