Variable four pipe heatpump chiller

Air conditioning apparatus, comprising:

• a plurality of modular heat pump chiller heater units arranged in a series arrangement,
• the series arrangement having a chilling side having at least one unit and a heating side having at least one unit;
• each of said modular units having a compressor,
• each of said modular units having at least one evaporator heat exchanger haying at least one cooling load heat exchange fluid inlet, at least one cooling load heat exchange fluid outlet, at least one cooling fluid inlet and at least one cooling fluid outlet,
• each of said modular units having at least one condenser heat exchanger having at least one cooling fluid inlet and at least one cooling fluid outlet,
• each of said modular units having at least one header pipe for cooling load evaporator heat exchange fluid,
• each of said modular units having at least one header pipe for condenser cooling fluid,
• isolation valves arranged between the header pipes of each unit,
• the isolation valves being closable to isolate the chilling side units from the heating side units,
• the number of units on each side being variable by virtue of the isolation valves,
• wherein the chilling side units are operatable chill simultaneous with the heating side units operating to heat.