Abstract: A heat exchange unit having a first heat exchanger 23 serving as an air heat source, a second heat exchanger 26 which is supplied with fluid such as hot water or the like to heat refrigerant, and a fluid amount adjusting mechanism 30,33 for adjusting the amount of the fluid to be supplied to the second heat exchanger, an air conditioner having the heat exchanger unit, and an air conditioning system having the air conditioner. The second heat exchanger 26 is disposed in a surplus space which is formed by the first heat exchanger 23 and an air blower 41 for promoting heat exchange between the air and the refrigerant flowing in the first heat exchanger 23. The upper portion of the case of the second heat exchanger 26 is provided with a fluid outlet port 100 and a refrigerant outlet port 101 while the lower portion of the case of the second heat exchanger 26 is provided with a fluid inlet port 103 and a refrigerant inlet port 104.