How do HVAC systems differ in Commercial buildings?

In warehouses, large business offices, malls, big department stores and other sizeable buildings, an A/C split-system approach is often used. The condensing unit normally exists on the roof and can be quite large. Alternatively, there may be many smaller units on the roof, each attached inside to a small air handler that cools a specific zone in the building.

In larger buildings, particularly in multi-story buildings, the A/C split-system approach can encounter problems. When running the pipe between the condenser and the air handler, you may either exceed distance limitations or the amount of duct work and the length of ducts can become unmanageable. At this point, it’s time to think about a chilled-water A/C system.

In a chilled-water A/C system, the entire air conditioner lives on the roof or behind the building. It cools water to between 40 and 45 degrees Fahrenheit. This chilled water is then piped throughout the building and connected to air handlers as needed. There’s no practical limit to the length of a chilled-water pipe if it’s well- insulated.

In all of the systems described above, air is used to dissipate the heat from the outside coil. In large systems, the efficiency can be improved significantly by using a cooling tower. The cooling tower creates a stream of lower-temperature water. This water runs through a heat exchanger and cools the hot coils of the air conditioner unit. It costs more to buy the system initially, but the energy savings can be significant over time, and in areas with low humidity, the system pays for itself fairly quickly.

Cooling towers come in all shapes and sizes and they all work on the same principle:

  • A cooling tower blows air through a stream of water so that some of the water evaporates.
  • Generally, the water trickles through a thick sheet of open plastic mesh.
  • Air blows through the mesh at right angles to the water flow.
  • The evaporation cools the stream of water.
  • Because some of the water is lost to evaporation, the cooling tower constantly adds water to the system to make up the difference.