a plurality of connecting pipes;

a main outdoor unit, which comprises:

a main casing having an air inlet and an air outlet;

at least one compressor supported in said main casing;

a refrigerant storage tank supported in said main casing;

a switching valve supported in said main casing;

a first outdoor heat exchanger supported in said main casing and connected to said compressor through said switching valve and at least one of said connecting pipes; and

a cooling tower which is supported in said main casing, and comprises:

a first water collection basin;

a first fill material unit provided underneath said first water collection basin;

a second water collection basin provided underneath said first fill material unit;

a third water collection basin provided underneath said second water collection basin;

a third fill material unit provided underneath said third water collection basin;

a water storage basin provided underneath said third fill material unit;

a second outdoor heat exchanger provided in said first water collection basin, said second water collection basin and said third water collection basin; and

a pump connected between said water storage basin and said first through third water collection basin, a predetermined amount of ambient air being arranged to pass through said first through third fill material unit and said first outdoor heat exchanger, a predetermined amount of cooling water circulating between said water storage basin, said first through third water collection basin, and first through third fill material unit, said cooling water in said water storage basin being arranged to be pumped to said first water collection basin for absorbing heat from said second outdoor heat exchanger therein, said water in said first water collection basin being arranged to be distributed on said first fill material unit, said cooling water being collected in said second water collection basin for absorbing heat from said second outdoor heat exchanger therein, said cooling water being arranged to flow down to said second fill material unit for being cooled by said ambient air, said cooling water being collected in said third water collection basin for absorbing heat from said second outdoor heat exchanger therein, said cooling water being arranged to flow down to said third fill material unit for being cooled by said ambient air, said cooling water being eventually collected in said water storage basin; and

an indoor heat distribution system, which comprises:

at least one indoor heat exchanger connected to said first outdoor heat exchanger, said second outdoor heat exchanger of said cooling tower, and said compressor through at least one of said connecting pipes; and

a ventilating device, which comprises:

a supporting frame having an air intake opening exposed to ambient air for allowing intake of air through said air intake opening;

a ventilating heat exchanging unit supported by said supporting frame, and connected to said refrigerant storage tank, said switching valve, and said first outdoor heat exchanger though at least one of said connecting pipes, said ventilating heat exchanging unit and said indoor heat exchanger being connected in parallel;

an energy efficient heat exchanger supported in said supporting frame at a position between said air intake opening and said ventilating heat exchanging unit such that said ambient air from said air intake opening is arranged to pass through said energy efficient heat exchanger before passing through said ventilating heat exchanging unit, said energy efficient heat exchanger being connected to said first outdoor heat exchanger, said second outdoor heat exchanger, and said refrigerant storage tank through at least one of said connecting pipes; and

a centrifugal fan supported in said supporting frame, said air conditioning and heat pump system being selectively operated between an air conditioning mode and a heat pump mode, wherein in said air conditioning mode, said switching valve is switched such that a predetermined amount of vaporous refrigerant is arranged to leave said compressor and guided to enter said first outdoor heat exchanger for releasing heat thereto, said refrigerant leaving said first outdoor heat exchanger being guided to flow through said second outdoor heat exchanger for releasing heat to said cooling water circulating in said cooling tower, said refrigerant leaving said second outdoor heat exchanger being guided to flow through said indoor heat exchanger of said indoor heat distribution system for absorbing heat from said indoor heat exchanger, said refrigerant leaving said indoor heat exchanger being guided to flow through said switching valve and flow back to said compressor to complete an air conditioning cycle,

wherein when said air conditioning and heat pump system is in said heat pump mode, said switching valve is switched such that a predetermined amount of vaporous refrigerant is arranged to leave said compressor and guided to flow into said indoor heat exchanger and said ventilating heat exchanging unit for releasing heat to a designated indoor space and said ambient air drawn from said air intake opening, said refrigerant leaving said indoor heat exchanger and said ventilating heat exchanging unit being guided to flow through said energy efficient heat exchanger for pre-heating said ambient air drawn from said air intake opening, said refrigerant leaving said energy efficient heat exchanger being guided to flow through said first outdoor heat exchanger for absorbing heat from ambient air passing therethrough, said refrigerant leaving said first outdoor heat exchanger being guided to pass through said switching valve and flow back to said compressor for completing a heat pump cycle.