Heat recovery VRV/VRF system/ VRV or VRF part 4

Schematic diagram of Heat recovery VRF System:

• It is an advanced version of the heat pump VRF.
• It is designed for both cooling and heating purposes.
• It can provide either cooling or heating and can also provide both heating and cooling at a time.
• In this system, there are three pipelines, hence it is known as the three pipeline systems.

            1) Hot gas pipeline 2) Suction pipeline 3) Liquid pipeline

For example:

• We have installed one heat recovery VRF System with 10 indoors. These 10 indoors will provide either heating or cooling at a time and can also provide both heating and cooling at a time means at the same time 5 indoors can provide cooling and another 5 indoors will provide heating(indoors are divided for heating and cooling as per the requirement e.g. 7-3, 6-4, etc).

Important Parts:

        1)Inverter compressor
        2)Accumulator
        3)Reversing valve
        4)The heat exchanger in the outdoor unit
        5)NRV
        6)EEV
        7)Separation tube
        8)Branch controller
        9)The heat exchanger in the indoor unit

Working:

Heating & cooling:

• Suppose Indoor 1 and Indoor 3 are supplying cooling air and indoor 2 is supplying hot air.
• Let's start with the compressor. It compresses the liquid refrigerant and converts into the hot gas refrigerant.
• This hot vapor refrigerant splits into two directions. Some refrigerants will go to the reversing valve and the remaining will go to the branch controller 1.
• On heating and cooling function, reversing valve 1 will open and 2 will be close. So hot liquid refrigerant will flow to the heat exchanger through reversing valve 1.
• The heat exchanger will reject heat from the hot vapor refrigerant and convert it into a hot liquid refrigerant.
• This hot liquid refrigerant will flow through NRV(because NRV has the same direction as refrigerant flow direction) and it will bypass the expansion valve.
• After passing the NRV, it will split into two different directions with the help of separating the valve and some hot liquid refrigerant will flow towards the Indoor 1 heat exchanger through an expansion valve and it will bypass the NRV.
• With the help of an expansion valve, the hot liquid refrigerant will convert into the low-temperature liquid refrigerant and it will go to an indoor heat exchanger. It will absorb heat from the room and convert it into saturated vapor refrigerant. 
• This vapor refrigerant will flow through branch controller 1 valve 'b' because it supplies cooling air. Hence branch controller 1 valve 'a' will close.
• After passing branch controller 1 valve 'b' saturated vapor refrigerant will go to the accumulator, which helps to supply only vapor refrigerant to the compressor, and then the compressor starts to compress the vapor refrigerant and it continues. In this way, indoor unit 1 will supply cooling air.
• Now coming to Indoor 2, high-temperature vapor refrigerant which comes from the compressor will go to the indoor 2 heat exchanger through branch controller 2 valve 'a'. Here the valve 'a' will open and valve 'b' will close because it supplies heating.
• This hot vapor refrigerant will reject heat into the room because room temperature is less than the refrigerant temperature. In this way, Indoor 2 will supply the heating.
• After heat rejection, it will convert into the hot liquid refrigerant and will flow through NRV (because it has the same direction as refrigerant flow direction).
• After passing through the NRV it will go to the Indoor 3 heat exchanger through an expansion valve.
• With the help of the expansion valve hot liquid refrigerant converts into the low-temperature liquid refrigerant and it will go to the indoor 3 heat exchanger.
• The heat exchanger will absorb heat from the room and converts into saturated vapor refrigerant and vapor refrigerant will go to the accumulator as same as the indoor 1 process. This way indoor 3 heat exchanger will supply cooling.

Only Cooling:

• In this case, all indoors will supply cooling.
• Let's start with the compressor. It compresses the liquid refrigerant and converts into the hot gas refrigerant.
• This hot vapor refrigerant splits into two directions. Some refrigerants will go to the reversing valve and the remaining will go to the branch controller 1.
• Here valve 'a'  will be closed for all branch controllers because in cooling case, hot gas line valves are closed.
• In this cooling function, reversing valve 1 will open and 2 will be close. So hot liquid refrigerant will flow to the heat exchanger through reversing valve 1.
• The heat exchanger will reject heat from the hot vapor refrigerant and convert it into a hot liquid refrigerant.
• This hot liquid refrigerant will flow through NRV (because NRV has the same direction as refrigerant flow direction) and it will bypass the expansion valve.
• After passing the NRV it will split into different directions with the help of a separating valve and some hot liquid refrigerant will flow to the Indoor 1 heat exchanger through an expansion valve and it will bypass the NRV.
• With the help of an expansion valve hot liquid refrigerant will convert into the low-temperature liquid refrigerant and it will go to an indoor heat exchanger and it will absorb heat from the room and convert into saturated vapor refrigerant. 
• This vapor refrigerant will flow through branch controller 1 valve 'b' as valve' a' is closed.
• After passing branch controller 1 valve 'b' saturated vapor refrigerant will go to the accumulator, which helps to supply only vapor refrigerant to the compressor, and then the compressor starts to compress the vapor refrigerant and it continues.
• In this way, all Indoors will supply cooling.

Only heating:

• In this case, all indoors will supply heating.
• In this case, the reversing valve 2 is opened, and reversing valve 1 is closed.
• Also, the valve 'b' of all branch controller is closed.
• Let's start with the compressor. It compresses the liquid refrigerant and converts into the hot gas refrigerant.
• This hot refrigerant will flow into the Indoor 1 heat exchanger through the branch controller as per the requirement and the remaining refrigerant will go to the next unit.
• The heat exchanger will reject heat to the room and hot vapor refrigerant will convert into hot liquid refrigerant.
• Then it passes through NRV bypassing the expansion valve.
• This process will happen in all units.
• At last, the total hot liquid refrigerant which comes from all indoors will go to the outdoor unit heat exchanger through an expansion valve where it will bypass the NRV.
• The heat exchanger will absorb the heat from the atmosphere and convert it into vapor refrigerant.
• This vapor refrigerant will go the accumulator through reversing valve 2.
• After passing the reversing valve 2, it will go to the accumulator which helps to sent only vapor refrigerant to the compressor. Again compressor compresses the refrigerant and the process continues. In this way all indoors supply heating.