Powerful approach to control for hotel air conditioning
A programmable logic controller for Mitsubishi Electric’s City Multi air-conditioning range allows easy automatic interlocking, with multiple units controlled through card-key readers, passive infra-red devices, window contacts and over-ride switches. This PLC system links to the G50 and baby G50 controllers and is designed for applications such as hotels where it has been difficult to accurately control individual units in each room because of the localised setting of each guest. Traditionally, guests switch the air conditioning to maximum when entering an unoccupied room because it had been off until the room was occupied. This caused discomfort for the guest until the room reached the desired temperature and also used more energy. Hotel owners can now guarantee that a room will not be too hot or cold before a guest checks in and monitor temperature and performance to prevent air conditioning using energy by running when it is not needed. The control system is activated by the room key card to set the system to a pre-arranged temperature of, say, 21°C. When the key card is removed, the PLC reverts to a setback programme. The system also overcomes the problem of guests leaving the air conditioning in cooling mode when they leave the room. The next guest tries to turn up the temperature, but the system is still in cooling mode and goes instead to standby, giving the hotel a frustrated and cold guest. With the PLC system, simply resetting the setpoint and mode to Auto 21°C when the room key card is in will ensure this problem never arises. Seb Desmottes, Mitsubishi Electric’s controls product manager, says, ‘The PLC system is a stand-alone unit that allows hotels to achieve this incredible level of control without the need for a dedicated computer. It allows us to connect everything locally to the indoor unit using digital inputs and outputs.’
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