Introduction: In many small and medium Hotels in India, the guest rooms are cooled with a window type air conditioner. There is also a ceiling fan which is used by the guest for uniform air movement and comfort. Now during the night-time the following is most likely to happen:

i)As the night progresses, the ambient temperature drops. Also since metabolic activity goes down during sleep, the cooling load reduces.
ii)The a/c will try to reduce cooling by switching off the compressor. But this has limitations and usually the guest will experience overcooling.
iii)At the same time, the speed of the fan will increase. This happens because the mains voltage during night-time goes up as most of the electrical loads such as lights are switched off. This speed increase of fan not only will consume more power but will also increase the noise level.
iv)Now, you have a twin problem; overcooling by the a/c and increased air draft.
v)The simplest and commonest way to tackle the above situation is to get up and reduce the fan speed manually (or even switch it OFF).
So; if there could be a device which will automatically reduce the speed of the fan in the above-referred situation, it will not only improve comfort but will save energy as well.
1.What will the controller consist of? :
It will include following components which will be wired up :
i)A voltage sensing transducer
ii)An output voltage correction unit
iii)A temperature sensor
iv)A Timer since the device is required to operate only during night-time and/or when the a/c is ON
v)An EPROM which will have a program to work on the combined inputs of voltage and temperature and in turn control the speed of fan.

2.Parameter Settings: In this controller, parameters such as voltage and air temperature have to be defined with a certain range. Some suggestions for these settings are :

Voltage: Normal range is 220 V ~ 240 V. It is observed that this
goes upto 260 ( or even 265 V) during low loads.This needs to be measured before designing the controller.

Temperature: Normal comfort range is 24 to 26 C. If the temperature goes below 22 C, one starts feeling discomfort. Hence the controller should reduce the speed if temperature goes below 22 C irrespective of whether the voltage is more than 240 V or not.