Heating, ventilating and air conditioning (HVAC) systems are often described as the "lungs" of a building1. They can range in size from small stand-alone units serving a single room to large centrally controlled systems that serve multiple rooms in a building. HVAC systems in modern public and commercial buildings can provide heating, cooling, filtered outdoor air and humidity control to maintain comfort conditions in the building2. However, not all HVAC systems are designed to accomplish all of these functions. Some buildings rely only on natural ventilation while others lack mechanical cooling equipment (air conditioning, AC), and many function with little or no humidity control. Thermal comfort is commonly maintained with heated or cooled air that is mechanically distributed throughout the building.