Temperature Remote Control

The question seems too broad since there are a number of different strategies to control the comfort level in a room. Is this a retrofit, new or existing installation? Does each room need individual control? Does humidity level matter? How sophisticated is your chiller control, does it supply more than just these 20 rooms, industrial processes, etc., etc. More detail will get to a more intelligent answer much quicker. (Just a little off topic, I like the idea of an occupancy sensor that controls the number of people in the room; the door locks and no one else is admitted, or does someone get launched out a window when the limit is exceeded? Where's Dilbert when we need him.)

>There would be an occupancy sensor that control the amount of people in the room

When HVAC systems is designed based on HVAC load calculation certain occupancy is considered . Room temperature is controlled by thermostat. Based on the signal chilled water is regulated in combination with various mortised valves either in AHU air candling unit or FCU Fan coil units. Based on the return chilled water temperature chiller works on full load or partial load depending upon the design. Building management system will provide the automation of HVAC system.

You need at least 20 air handlers to serve each of your 20 rooms. Each AH has a coil and a supply fan. A solenoid is opened on a call for cooling. Chilled water is then allowed to flow through the coil. So you need one common supply line and return line piped to your chiller. You never said what chiller you have but it has to have capacity control since all 20 valves would rarely be opened at the same time.

I hope that helps, there's quite a bit more to it but that's your basic system.