Introduction to Energy Management

Week/Lesson 11 Control Systems for Occupant Comfort

 Describe control systems from the functional block perspective  Define terms commonly used in the controls industry  Explain the characteristics of each control response Control Systems for Occupant Comfort Learned Outcome

 Give examples of temperature, humidity and pressure sensors  Describe how loads affect the control system under heat gain and heat loss conditions  State the operational differences between pneumatic and electric actuators Control Systems for Occupant Comfort

The fundamental control loop  Final conditions Results of control system’s efforts Temperature, humidity, pressure  System feedback Provides sensor with data Closed loop Control Systems for Occupant Comfort

Sensors  Measure controlled variables  Send signal to controller Controllers  Analyze input from sensor  Send signal to controlled devices Control Systems for Occupant Comfort

Controlled devices  Regulate water, steam or air flow  Valves and/or dampers  Actuators provide physical movement  Move manipulated devices  Control temperature, humidity and pressure Control Systems for Occupant Comfort

Control system types  Self-contained control systems  Pneumatic control systems  Electric control systems  Analog electronic control systems  Digital electronic systems Control Systems for Occupant Comfort

Sensors  Provide information about monitored condition  Need communications paths  Analog inputs ( i.e., temperature)  Binary inputs ( i.e., ON-OFF) Control Systems for Occupant Comfort

Temperature sensors  Single point or averaging  Bulb and capillary  Bimetal/Rod and tube  Sealed bellows  Thermocouple, resistance, thermistors Control Systems for Occupant Comfort

Pressure sensors  Low or high pressure ranges  Psig, psia or inches of water column  Piez-resistive sensing New electronic technology Micromachined silicon diaphragms Control Systems for Occupant Comfort

Controllers  Create system response  Two-position Open/closed, ON/OFF Operates with a differential Set point overshoot Control Systems for Occupant Comfort

 Two-position with anticipation Prevents set point overshoot Falsely loads thermostat  Floating Gradual, continuous action Used in systems with slow load changes Control Systems for Occupant Comfort

 Proportional control Relationship between controller and controlled device Proportional band  Range of controlled variable  Controlled device – open or closed Offset = control point – set point Control Systems for Occupant Comfort

 Proportional plus integral control Maintains set point (minimum offset) Automatic reset  Proportional plus derivative control Maintains set point Overshoot is eliminated Control Systems for Occupant Comfort

Controlled devices  Valves – water and steam flow devices  Dampers – air flow devices  Made up of: Actuators – causing physical movement Manipulated devices – moved by actuators Control Systems for Occupant Comfort

Valves  Two way – straight through flow  Three way – straight through flow with bypass and mixing capabilities  Normally closed/normally open  Normal position is the fail-safe position Control Systems for Occupant Comfort

Dampers  Parallel blade/opposed blade  Normally open/normally closed  Outdoor damper Fail-safe is normally closed Prevents freezing air from entering the space Control Systems for Occupant Comfort

Actuators for valves and dampers  Provide force to stroke the manipulated device  Must overcome pressure differences  Must overcome frictional forces  Pneumatic (air) or electric Control Systems for Occupant Comfort

HVAC processes  Control agents – heating, cooling, humidifying, dehumidifying  Operations Regulation – valves and dampers Automatic controls – regulate flows Control Systems for Occupant Comfort

Final conditions  Results of control system efforts  Should be within desired tolerances Feedback  System feedback  Transmits data to the sensors Control Systems for Occupant Comfort

Closed loop systems  Feedback controls the HVAC process  Sensors measure final conditions Open loop systems  Used to correct for load changes  Sensor does not monitor the final conditions Control Systems for Occupant Comfort