HVAC (heating, ventilating, and air-conditioning) refers to the equipment, distribution network, and terminals that provide either collectively or individually the heating, ventilating, or air-conditioning processes to a building.

HVAC accounts for 40% to 60% of the energy used in U.S. commercial and residential buildings. This  represents an opportunity for energy savings using proven technologies and design concepts.

HVAC systems have a significant effect on the health, comfort, and productivity of occupants. Issues like user discomfort, improper ventilation, and poor indoor air quality are linked to HVAC system design and operation and can be improved by better mechanical and ventilation systems. In existing buildings, envelope upgrades are often necessary to maximize comfort and energy efficiency, such as reducing envelope leakage. (Click on the link below to read the complete article.)

U.S. Department of Energy's Building Technologies Program: Heating & Cooling Systems

http://www.eere.energy.gov/buildings/info/components/hvac

Energy Star: A Guide to Energy Efficient Heating & Cooling

http://www.ecobroker.com/userdef/articles/HVAC/EStar.Heating.Cooling.pdf

http://www.energycodes.gov/implement/pdfs/lib_ks_selecting_a_home_heating_system.pdf

http://www.ecobroker.com/userdef/articles/HVAC/CoolingNaturally.pdf

http://www.ecobroker.com/userdef/articles/HVAC/ProgramThermostats.pdf

http://www.ecobroker.com/userdef/articles/HVAC/Cooling.with.Fans.Vents.pdf