The refrigerant piping is made up of copper tubing and it connects the indoor and the outdoor unit (see images above). The refrigerant at low temperature and low pressure leaves the expansion valve and enters the copper tubing, which is connected to the evaporator or the cooling coil at the other end.
The distance between the indoor and the outdoor unit can be short or long depending on the distance at which the open space is available in the home or office building. The longer the distance longer is the refrigerant piping between the two. When the refrigerant flows from the indoor unit to the outdoor unit in the tubing there is some loss of the cooling effect on the way, hence the distance between the indoor and the outdoor unit should be kept as minimum as possible. For the distance up to 15 meters there is not much appreciable loss of the cooling effect, however beyond that the losses become higher.
The refrigerant inside the tubing is at very low temperature and length of piping between and outdoor unit and indoor unit is quite long. Further, the tubing is exposed to the open atmosphere which is at very high temperature. Due to this, if the tubing is left uncovered all the cooling effect will be lost to the open atmosphere and by the time the refrigerant enters the cooling coil its temperature will already be too high and the purpose of producing the cooling effect will not be served. To avoid this, the refrigerant tubing connecting the indoor and the outdoor unit is covered with the insulation. This prevents the loss of the cooling effect to the atmosphere and low temperature refrigerant will produce the desired cooling effect inside the room.
After producing the cooling effect inside the room in the indoor unit, the refrigerant has to comeback to the outdoor unit for getting compressed and re-circulating. There is another refrigerant tubing that connects the indoor and the outdoor unit so that the refrigerant can travel from cooling coil back to the compressor. This tubing is also covered with insulation so that the refrigerant enters the compressor at minimum possible temperature to increase the refrigeration efficiency of the air conditioner. Thus there are two tubing connecting the indoor and the outdoor unit and both are covered with the insulation tape.
The refrigerant tubing are made up of copper since it is highly ductile and malleable element. The tubing can be easily manufactured from this material and they are flexible enough so they can turned into angles and coiled easily. The copper tubing used for condenser and evaporator facilitate high rate of heat conduction.
