HVAC is the equipment that heats, cools and moves the air in a building. The letters stand for heating, ventilation and air conditioning. In most Indian buildings, the main job is cooling. In a large office, mall or hospital, cooling usually uses more electricity than anything else in the building.
A home or a small shop uses split air conditioners, one for each room. A large building cannot do this. Instead, it uses a central cooling plant. A chiller, a large machine in the basement or on the roof, makes cold water. Pumps send this water through pipes to every floor. On each floor, an air handler, a large box with a fan, blows the building's air across coils that carry the cold water. The cooled air then travels through ducts into the rooms. The water, now warmer, returns to the chiller to be cooled again. The chiller throws the heat it has removed out of the building, usually through a cooling tower on the roof.
Consider a ten-floor office building in Noida, with 2 lakh square feet of office space. Its engineers measure cooling in tonnes of refrigeration (TR). One TR is the cooling needed to melt one tonne of ice in a day, which is about 3.5 kilowatts of heat removed. An office needs roughly one TR for every 350 to 400 square feet. So this building needs about 500 TR. Two chillers of 300 TR each share the load, so the building still has some cooling if one chiller fails. The chillers send water out at about 7°C, and it comes back at about 12°C.
On a June afternoon, the whole cooling plant, with its pumps and fans, may draw about 400 kilowatts. At a commercial tariff of about ₹10 per unit, that is about ₹4,000 an hour. So small savings add up. A variable frequency drive (VFD) lets each pump and fan run only as fast as the load needs, instead of at full speed all day. The building automation system (BAS) raises or lowers the water temperature as the load changes, and switches off one chiller in the evening. India's Energy Conservation Building Code, issued by the Bureau of Energy Efficiency, sets minimum efficiency levels for the cooling in new commercial buildings.
A modern chiller also reports its pressures, temperatures and power use to its maker over the internet. This is the industrial Internet of Things (IIoT). So the maker can sell a service contract along with the machine, and spot a failing part early. Planned services and repairs are logged in the owner's computerised maintenance management system (CMMS).
How is building cooling different from data centre power and cooling? An office is cooled for people, mostly in the daytime. A data centre is cooled for servers, all day and all night, and each square foot produces far more heat.