Abstract: The present disclosure provides an air conditioner comprising: an indoor heat exchanger to exchange heat between underground water and indoor air; an outdoor heat exchanger to exchange heat between underground water and outdoor air; a well; an underground water tank to store underground water; and a water pump to pump water from the well to the underground water tank. The indoor heat exchanger comprises a copper tube running through a row of parallel aluminum panels. Air is sucked by a fan through the indoor heat exchanger in the direction opposite to the underground water flow direction in the copper tube. Air is then passed through an evaporator unit of a compressor to be dehumidified. The underground water, after exchanging heat with the air to reach approximate room temperature, goes through a condensing unit of the compressor to release heat.