we often find multiple units connected together within a commercial building with this setup all units can provide heating or all units can provide cooling but importantly some can provide heating while some can provide cooling at the same time each indoor unit is connected to a branch controller which contains a number of valves to direct the flow of refrigerant to provide either heating or Cooling in this system we have three pipes running to each branch controller the suction line with the superheated gas the liquid line providing Cooling and the hot gas line providing Heating we also have a variable speed compressor located outside in cooling mode the compressor sends the hot refrigerant to the outdoor unit to reject the Heat this will then flow to each of the branch controllers where it flows through an expansion valve and then through the indoor unit to provide Cooling and also collect The Unwanted heat it then brings us back to the compressor in heating mode the compressor sends the hot gas to the indoor units where it provides heat to the rooms and then flows to the outdoor unit where it will flow through an expansion valve before entering the outdoor unit to absorb the thermal energy of the ambient outdoor air this then flows to the compressor so that it can be compressed up to a usable temperature and pressure and then sent around the building in mixed mode the hot discharge of the compressor is sent to both the indoor unit as well as the outdoor unit when it flows to the outdoor unit it will then flow to the units requiring cooling this will then flow back to the compressor to repeat Heat this cycle meanwhile the compressor is also sending hot gas to the indoor units which are requiring Heating the refrigerant exits these units and will flow to the units requiring cooling so that way the same system can provide both Heating and Cooling at the same time if we consider a larger system with multiple indoor and outdoor units in full cooling mode all indoor units are collecting heat and all outdoor units are rejecting heat in full heating mode all outdoor units are collecting heat and all indoor units are rejecting heat and then in mix mode if two indoor units require Heating and two require Cooling and the loads are equal then the outdoor units are not used the thermal energy is simply transferred between the units so we have a full heat recovery the compressor still runs to push the refrigerant around the system though if the heating and cooling loads are not equal and we have for example three indoor units providing Heating and one unit providing cooling then we will need to run some outdoor units to collect more thermal energy as the single indoor unit in cooling mode will not be able to collect sufficient thermal energy to provide the other units with heating check out these videos to continue learning about Refrigeration engineering and I'll catch you there for the next lesson don't forget to follow us on Facebook LinkedIn Instagram Tick Tock Twitter and the engineeringmindset.com