Climate control and comfort in modern buildings is a major design issue. Heating, ventilation and air conditioning (HVACHVACHVAC) systems help to control the climate, and keep occupants comfortable by regulating the temperature and air flow. HVAC systems are also important to occupants' health, because a well regulated and maintained system will keep a home free from mold and other harmful organisms. In some environments, such as museums, HVAC systems are vitally important for the preservation of historic artifacts.