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The multi-source heat pump functions as an air-to-air heat pump during a cooling mode of operation during which heat is withdrawn from the air to be conditioned by standard indoor evaporator coils, said heat being rejected to the outside air by a standard outdoor condenser coil.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. The closed liquid circulating loop interconnects the heat pump chiller, the waste heat recovery coil and a heat storage means and may also be connected to a supplemental heat source and a solar heat collector. It is also contemplated that one or more remote water source heat pumps may be connected into the closed liquid circulating loop for heating and cooling remotely located spaces.