Abstract: An HVAC system for a building of the type that has an interior zone and a perimeter zone includes an economizer type air conditioning unit for the interior zone and a multi-source heat pump for the perimeter zone. The interior zone economizer type air-conditioning unit has a waste heat recovery coil disposed at the exhaust air dampers and connected in a closed liquid circulating loop for recovering heat from the exhausted air. The multi-source heat pump functions as an air-to-air heat pump during a cooling mode of operation during which heat is withdrawn from the air to be conditioned by standard indoor evaporator coils, said heat being rejected to the outside air by a standard outdoor condenser coil. The heat pump operates as liquid-to-air heat pump during the heating mode of operation during which heat is extracted by a chiller from the closed liquid circulating loop and is discharged to the conditioned air through the indoor coils which act as condensers during the heating mode of operation.

Abstract: A variable air volume air conditioning system is provided with thermostat controlled variable air volume terminal boxes for controlling the volume of constant temperature conditioned air provided to each space to be conditioned. The conditioned air is delivered through a short pressure recovery duct to a trunk duct by a centrifugal fan having forward curved blades. The trunk duct pressure is maintained substantially constant by control vanes disposed at the recovery duct outlet, said control vanes being responsive to an increase in duct pressure to close the duct outlet and unload the fan, thereby reducing the energy consumed by the fan. Economizer operation is provided by the use of return air dampers and outside air dampers controlled in response to outside air temperature and air supply duct temperature to mix outside air and return air to reduce the amount of mechanical refrigeration required.