Anyone who has been in a well air-conditioned store in the summer or stepped into a warm office in the dead of winter has an appreciation for commercial HVAC systems. Every commercial building is equipped with a heating, ventilation, and air conditioning (HVAC) system to keep its occupants comfortable and healthy in any weather.
This part of an HVAC system is perhaps the simplest to achieve. Most homes make use of a central heating furnace, which burns natural gas or wood. Electric heat can be used but is more often found in small space heaters or baseboard heaters to supplement a central heat system and prevent cold spots. Hotels and apartments might use room-specific heaters, allowing each occupant to set their desired temperature. In a commercial setting, it is not enough to simply produce heat. It must be distributed evenly and throughout the entire building. Often, heating ducts and large fans are used to force warm air to its destination. Water or steam can also be means of distribution, with pipes connected to radiators or buried in flooring. The cold return water then runs back to a central boiler or other source of heat. In some locations, this could even be a geothermal well that draws hot water from deep underground.
The second aspect of an HVAC system is ventilation, which is simply the replacement of stale interior air with fresh exterior air at regular intervals. This reduces unwanted humidity, unpleasant smells, and airborne contaminants while bringing in sufficient oxygen to keep the building occupants safe, healthy, and comfortable. Proper ventilation also improves heating efficiency. Warm air rises and can become trapped in ceilings, causing heating systems to heat the heavier, cooler air more than necessary. Fans that circulate the air in a room or building allow the heat to be more evenly distributed and reduce the demand on heaters. In hot weather, the movement of air increases evaporation, which has a cooling effect, and can be used to vent humid air for additional comfort.
The final part of an HVAC system is the most complex: air conditioning. A typical air-conditioner is made up of four parts: the condensing coil, the compressor, the expansion valve, and the evaporator coil. The refrigerant material begins as a gas, which is then compressed to a hot liquid and pumped to the condenser coil. The liquid loses excess heat to the outdoor environment before it is moved to the evaporator coil. There it depressurizes and evaporates back to a gas, which has a cooling effect. The gas then returns to the compressor to repeat the cycle while the now-cold evaporator coil cools the room, usually by means of a fan that blows warm room air over the cold coil. In commercial applications, this concept is simply scaled up, with much larger coils, compressors, and fans. The evaporator coils also act as dehumidifiers, as the cold coils actually cause moisture in the building to condense on them, which is then collected and drained away.
In a new building installation, a large central unit will often be installed, with large ducts routed to every room in the building. However, this method is difficult to use when retrofitting an existing building, as the space required for ductwork is often not available. Instead, smaller split-systems can be used. They are small ductless units that provide HVAC to one or a few rooms each. Because of their small size and versatility, they can be added to nearly any room or building and have the added benefit of individual room temperature control. And because they are typically all-electric, there is no need to run gas lines or other sources of combustion for heating.
HVAC systems, when properly installed, are often taken for granted. But their necessity in providing clean, comfortable air cannot be understated.