Four words are hiding in HVACR definition.
✸ air conditioning;
Another word that can describe HVACR is a Comfort. No matter what weather is outside, inside the building you have acceptable indoor temperature and air quality. HVACR belongs to the mechanical engineering field including knowledge of thermodynamics, fluid mechanics, and heat transfer.
In the 21st century, we cannot imagine our life without HVACR technologies. In our houses, offices, laboratories, schools, colleges, factories, we can control temperature and humidity with air conditioners and heaters using outside air. In the restaurants and kitchens, people use fridges and freezers, so we have no worries about the safety of food anymore.
Every kid knows that an air conditioner makes the air in the house cool and fresh even when windows are closed.
How does it work? Replacing air in any room is a complicated process, which includes temperature and moisture control, oxygen replenishment and removal of odors, airborne bacteria and different gases as carbon dioxide. This process is constant and complicated. The air circulates inside the building.
Now all functions of HVAC system are included in one interior climate control system. You have no need to buy an air conditioner and heater separately. Modern houses have them altogether built in.
Anyway, it is not as simple as it seems. There are different kinds of HVAC systems specified for different types of buildings. We cannot put the same system in the skyscraper apartment and small village house. Engineers develop new methods of building every day. That is why specialists work on new inventions in HVAC area all the time.
Building standards have to aim the HVAC standards. In the USA, these standards are required by International Mechanical Code, with adoption to states law.