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| Deadband and Hysteresis (Staged Equipment)

Objective - Reduce short cycling to increase energy efficiency and increase the lifespan of the equipment. 

Deadband- This is your desired setpoint. In a 75F system, you can set cooling and a heating setpoint.

Hysteresis- If a control unit constantly tried to stay very tight to a particular heating or cooling temperature, it would cycle on and off more than necessary for comfort and would also reduce the energy efficiency and life of the heating/cooling unit.  Specifying a number for hysteresis, allows the system to cool or heat passed the set point, reducing unneeded cycling.

Process- For a more detailed explanation of the cooling control process, you can see from the example in the diagram below, there is a desired cooling setpoint of 74F, with a 2 degree deadband and a .5 degree hysteresis. As the zone warms past the Cooling Deadband (desired setpoint), the cooling valve will open, and the first stage fan will engage. If the zone temperature rises another 2 degrees, the second stage fan will engage.  When the zone temperature starts declining, the second stage fan will disengage once it reaches Cooling Deadband (74F in this example). The zone will continue to cool to the hysteresis value (73.5F in this example), at which point, the fan will disengage, and the cooling valve will shut.


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