Abstract: A fan coil air conditioning system comprises at least one fan coil unit, the fan coil unit comprising a heat exchanger, at least one fan, a return air inlet and a conditioned air outlet. The heat exchanger comprises a cooling water connection for connecting to a source of cooling water, and a heating water connection for connecting to a source of heating water. The cooling water connection and the heating water connection are each provided with a respective motorised regulating flow valve. The system further comprises a controller operative to receive an air temperature signal and fluid temperature signals, and also a duty signal indicative of the temperature and volume flow rate of the conditioned air required for the conditioned air outlet in question. The controller subsequently generates a valve control signal to control the motorised flow valves.