HVAC

HVAC is simply how a building heats, moves air, and cools. When you walk into a room and it feels comfortable without thinking about it, the HVAC system is doing its job. When a studio feels stuffy, a corridor is freezing, or a café feels fresh and lively, that’s HVAC too, either working well or struggling.

You meet HVAC in many small ways: the grille near the floor blowing warm air in winter, the cool draft from a ceiling diffuser in summer, the constant low hum of a fan somewhere above the ceiling. Even the feeling of “fresh” versus “stale” air is part of this system.

Think of three spaces you use often (home, classroom, café). Which one has the best “invisible comfort,” and why do you think that is?

Most HVAC systems, no matter how complex, are built from a similar set of parts. There is equipment that adds heat (like a furnace or boiler), equipment that removes heat (like an air conditioner or chiller), something that moves air (fans, ducts, grilles), and a way to filter and control it all.

In a small building, many of these pieces are combined into a few compact units. In a large building, they spread out: air-handling units in mechanical rooms, boilers and chillers in plant spaces, ducts weaving across ceilings, and a network of sensors and controllers. Once you know these basic “characters,” you can start to recognize them in any building you visit.

Next time you enter a building, can you spot at least one visible part of the HVAC system (an outdoor unit, intake grille, duct, or diffuser)?

Heating systems add energy so indoor spaces stay warm when it’s cold outside.

A furnace heats air directly and sends it through ducts. A boiler heats water, which then flows to radiators or underfloor pipes that gently release warmth into rooms.

A heat pump works differently. It doesn’t just create heat; it moves heat from one place to another using a refrigeration cycle. In winter, it can pull heat from outside air (or the ground) and bring it indoors. Many heat pumps can reverse in summer, acting as air conditioners. This “two-in-one” ability and higher efficiency are big reasons heat pumps are becoming more common.

In the building you live in now, do you think heating is provided by warm air (furnace), warm water (radiators), or something else?

Cooling systems don’t actually “blow cold” into a room. Instead, they remove heat. Inside an air conditioner, a refrigerant flows in a loop. When the refrigerant evaporates at low pressure in the indoor coil, it absorbs heat from indoor air, making that air cooler. When it condenses in the outdoor unit, it releases that heat to the outside.

Cooling also affects humidity. As warm, moist indoor air passes over a cold coil, water vapor condenses and drains away. That’s why air-conditioned spaces can feel more comfortable even if the temperature number on the thermostat doesn’t seem extremely low. Lower humidity makes it easier for your body to cool itself.

Have you ever seen water dripping from an outdoor AC unit or a pipe? That’s condensed moisture. Where in your building do you think that water goes?

Ventilation is about fresh air in, stale air out.

People, materials, and activities all add pollutants to indoor air: carbon dioxide, odors, particles, and chemicals from furniture or cleaning products. Without fresh air, rooms can quickly feel heavy and unpleasant.

A good HVAC system brings in outdoor air in controlled amounts, mixes it with indoor air, filters it, and distributes it to occupied spaces. In some buildings, mechanical fans and ducts do this work; in others, operable windows and atriums help with natural ventilation. Filters and humidity control are part of indoor air quality too, helping reduce dust, pollen, and extreme dryness or dampness. Think about a room where you sometimes feel sleepy or foggy. Do you think the problem is temperature, lack of fresh air, or both?

Even the best heating or cooling equipment is useless if the air never reaches people. That’s the job of airflow and ductwork. Ducts act like highways for air, carrying it from central units to rooms and back again. Fans create the pressure that pushes and pulls air through this network.

If ducts are too small, too long, or badly arranged, you get noise, uneven temperatures, and wasted energy. If they are well designed and sealed, air arrives quietly and evenly, and each room can feel consistent. In some systems, instead of a single big duct network, smaller units in each room handle the job locally; a different strategy, same goal: get conditioned air to where people are.

Have you noticed certain spots in a room that always feel drafty or dead-still? What do those spots tell you about how air is (or isn’t) moving?