1. Control Principles, Terms and Concepts Lesson 9
Building Operator Certification Level I (BOCI)
Building Systems: Controls
CUNY School of Professional Studies
CUNY Building Performance Lab
The BOC
Control Principles, Terms and Concepts
Lesson 9

2. Lesson 10 Agenda Control principles, terminology and concepts.
Types of controls and control systems.
Sequences of operation.
Maintenance of Controls.

3. What are Controls?
“Controls are simply devices that try to duplicate the human thought process. With HVAC controls, the controls are designed to carry out the thoughts and desires of the HVAC system designer.”
Definition by American Society of Heating, Refrigeration & Air Conditioning Engineers (ASHRAE)

4. What are Controls?
Controls are the brains of the HVAC system: they directly impact energy use, Indoor Air Quality (IAQ), facility safety and the environment.
Not just temperature! What else do we control?
Energy
Relative Humidity/dew point
CO2/CO
Pressure
Velocity, Flow, Air Changes, and more
All of these variables can be controlled and more. Energy is not something that we consider as being directly linked to controls, but controls indirectly manage energy use and the costs associated with the use of energy.
Controls can be as simple as a single switch, or as complex as an entire building automation system. The consistent feature of controls, no matter how simple or complex, is that they control inputs and outputs of a system. An example of an input would be space temperature. An example of an output would be moving the hot water valve. In this example the controller reads the space temperature, compares it to a set point of 72 degrees Fahrenheit, and then calculates the needed position of the hot water valve to make the space temperature reach the set point of 72 degrees Fahrenheit.

5. Control Acronyms ATC – Automatic Temperature Control
EMS – Energy Management System
EMCS – Energy Management Control System
BMS – Building Management System
BAS – Building Automation System
CSCS – Central Supervisory Control System
DDC – Distributed Digital Control

6. Control Concepts - Terminology
Controlled variable, the temperature, humidity, pressure, velocity, or other condition being controlled
Sensor, the device that measures the condition of the controlled variable. In an open system the measurement signal (pneumatic, electric, electronic) is sent to the controller.
Set point, the desired value of the controlled variable
Controller, the device that compares state of controlled variable from sensor (temp, pressure, etc) and signals the controlled device for corrective action if needed: a comparator.
Controlled device, the hardware (valve, damper, variable speed drive (VSD), electric reheat, etc) manipulated by the controller.
Control agent, the medium (gas, chilled water, conditioned air) manipulated by the controlled device.
Control process, the apparatus being controlled; steam heat, DX system, fan. The control process reacts to the control agent output and effects change in the controlled variable.
Control loops, open or closed.
Actuator, manipulates the controlled device, e.g. motor on a hot water valve to a heating coil

7. Control Concepts – More Terms
Control point is the actual value of the controlled variable such as the space temperature.
Deadband occurs when there is neither heating nor cooling.
Error is the difference between control point and desired set point
Range and span refer to the variable points over which the sensors and controllers operate. Range refers to the sensing elements. Span refers to the controller.
Throttling range is the amount of change in the controlled variable that causes the controlled device to move from one extreme to the other, from full open to full closed.
Authority refers to the priority ranking of two, or more, sensors.
Calibration is the verification, and adjustment if necessary, of the accuracy of a sensor or controller. Calibration should be done regularly.
Analog and digital refer to the input/output signal type. Analog is a varying parameter such as temperature or pressure and can have many numbers. Digital is two state (0 or 1) and can represent on/off or open/closed.
A thermostat can be any sensor and controller combination.
Time delay relays are used to deliberately provide time delays in a control action. For, example, time delay relays are used in boiler systems to delay the firing of the burner until the boiler has completed the pre-purge cycle.

8. Control Loops Closed Loop Control Thermostat for room temperature
sensor
controller
controlled variable
Closed Loop Control
Thermostat for room temperature
Boiler Pressure Control
Lighting Level Control with Dimming
Open Loop: No feedback. Controller adjustments not based on information from controlled variable (for example, outdoor temperature reset on boiler).
Closed Loop: Feedback. Measures changes to controlled variable and actuates controlled device in response (for example, variable air volume (VAV) controlling space temperature.
For example, a street-lighting system controlled by a timing device is an open-loop system. At a given time each evening, a mechanical device closes the circuit and energy flows through the electric lines to light the lamps. If the lights should be needed on a dark, stormy day the timing device wouldn’t recognize this need and would not activate energy inputs. A closed-loop street lighting system would sense the level of daylight outside, and signals the light to turn on when there is only a certain amount of daylight available. The level of daylight selected would be the set point: the lights would recognize the need to turn on during dark, stormy weather, without an external force acting on it.
sensor
controller
controlled variable
Open Loop Control
light sensor for outdoor lights
motion sensor for indoor lights
time-clock for on/off of any device

9. Control Concepts Control action Two position control
On/Off or Open/Closed Control
Modulating Control (P, PI, PID)
Proportional: controller output signal is in proportion to the error (deviation from set-point)
Proportional-Integral: adds a mathematical value to adjust the control action in relation to the average error
Proportional-Integral-Derivative: looks at the rate of change of the controlled variable
There are two main types of control actions, two-position and modulating. The controlled device on two position controls, either an actuator or a valve, is going to be fully open or fully closed. An example of this would be a normal light switch without a dimmer. Modulating controls allow the output to be varied based on the continual adjustments of the controlled device (for example, a light switch with a dimmer). It is not fully on or fully off, but can be at a level in between based on the controller.
Both two-position and modulating controls can have either open or closed loops. Adjust the switches on the screen to see the difference between two-position and modulating controls. In this example, these controls would both be open loop because they do not sense feedback from the controlled variable. They are controlled from an external source, humans.

10. 2 Position Control Digital (Two position) Output
Upper Limit and Lower Limit (for example, cooling on at 78 and off at 76)
Change of output based on analog input crossing limits (i.e. temperature going above or below limits)
Applications
Temperature control
Freezestats
Moderate to slow responding control loops
Step Control: Multi speed motors, multi stage burners, multi stage compressors
Two-position controls have a digital output, fully on or off or fully open or closed. They have an upper and lower limit; for example, hot water valve controlling heating of a space would switch to fully closed when room temperature hits 70 degrees and would switch to fully open when room temperature hits 68 degrees. Changes in output are based on the analog input, temperature in this case, crossing these upper or lower limits.

11. Two Position Control
An example of this type of control is an exhaust fan that comes on/off to maintain space temperature. Could come on at 90 and off at 85.

12. Modulating Control PID Terms / Mathematical Relationships
V=output of controller
V= proportional control + integral control + derivative control
V= Kp(e) + Ki (∫edt) + Kd (de/dt)
e=error
t=time
d=differential
∫ = integral symbol
Kp=proportional gain
Ki=integral gain
Kd=derivative gain
Controller does the math and when you tune the control loop these are the variables that you are adjusting. Two position controls are fairly simple, but modulating controls use the error, or deviation from the set point, to control the output. The output on modulating controls varies continuously, and is not limited to being fully open or fully closed. There are three types of modulating controls, proportional, proportional-integral, and proportional-integral-derivative.

13. Proportional Only Control
Simple / Common
“Happy with Offsets” which means once control loop settles out there will be a difference between desired value and set point
@ set point, e=0
Proportional gain is the amount of change in controller output signal for a given change in the difference between controlled variable and its set point (error)
Kp=controller proportional gain
Large gain, small offset
Large gains can cause hunting
When tuning control loops this is the variable you are adjusting

14. Proportional (P) Control
An example of this type of control is a hot water control valve modulating to maintain a temperature set point. There is always offset. The controlled variable never stays at set point.

15. Proportional + Integral (PI) Control
V= Kp(e) + Ki (∫edt)
Most Common
Minimizes or eliminates offsets
The longer error exists for, the larger the integral term (∫edt) and hence the larger the controller output (V)
Ki=controller integral gain
When tuning control loops this is the variable you are adjusting

16. Proportional plus Integral (PI) Control
An example of this type of control is a chilled water control valve maintaining 55 degree F air temperature on an air handling unit. There is no offset. The controlled variable gets to set point and stays there.

17. Proportional + Integral + Derivative (PID) Control
Applies the brakes to the integral term
Very fast response
Used in industrial processes and rocketry (in-space flight controls)
Not common in hvac (except lab air flow tracking, etc.)
Proportional plus integral plus derivative controls are used more in industrial processes

18. Types of Controls and Control Systems

19. Classification by Energy Sources
-Pneumatic
-Self Acting
-Electric
-Distributed Digital Control (DDC)

20. Pneumatic Controls Powered by compressed air Inherently modulating
Simple
Low cost
Reliable
Explosion proof
Compressed air is an open protocol
Obsolescence has been predicted since 1950’s (not installed in new buildings, many remain in existing buildings)

21. Pneumatic System Diagram
This is an introduction to the section. Nothing in particular that they need to know from the image – just to see the parts.

22. Pneumatic Control - O&M
What are things that need routine maintenance?
Belt
Pressure settings
Compressor wear
Oil
Moisture
system leakage will increase compressor run-time

23. Pneumatic Thermostat
What are these? Room Thermostats. What are they used for? Controlling room temperature
Middle is sensing element (bimetal) Right is pneumatic ports/channels/nozzles
The right is like a crossection of the thermostat on the wall.
The bullets are the takeaways.
How do these work? They utilize springs, mechanical levers, valves/nozzles and bellows that are all energized by compressed air .
Why are these devices hard to keep calibrated? Parts wear out.
Why might there be air leakage? Fixable? Sometimes it is fixable. Some are designed to leak air (bleed type)

24. Example of Pneumatic Action
Direct Acting / Normally Open (DA/NO)
Direct-acting: increase in the level of the sensor signal results in an increase level of controller output (outlet air pressure to actuator)
Stem down closes valve
Normally retracted valve stem
Air pressure pushes diaphragm/stem down
Reverse Acting / Normally Closed (RA/NC)
Reverse-acting: increase in level of sensor signal results in decreased controller output
Stem down opens valve
Normally extended stem
Air pressure pushes diaphragm/stem up
These could be

25. Pneumatic Thermostat Action
Temperature is falling
Air pressure is falling
Direct acting
Temperature is rising
Air pressure is rising
Direct acting
Temperature is rising
Air pressure is falling
Reverse acting
Temperature is falling
Air pressure is rising
Reverse acting

26. Pneumatic Thermostats
Day/Night Set Points
Heat/Cool Set Points
Different manufacturers use different pressures:
Mfr
Day (psi)
Night (psi)
Honeywell 13 18
Johnson 15 20
Siemens 25
Barber Coleman
Robertshaw 16
Set point stays at the manufacturer’s set point

27. Pneumatic Actuators
Metal cylinder, piston, flexible diaphragm and a spring
Normal position versus actuated position
What does “Normal” mean in controls?
The de-energized position. The failed position.

28. Pneumatic Actuators
Required air pressure is determined via spring range.
Honeywell book pages 74 and 75: Figures 26 & 27:

29. Pneumatic Control Valves
DIAPHRAGM
Diaphragm

30. Pneumatic Valve Actuators
NO (normally open)
Spring opens valve
Valve fails open
Valve and actuator have same action
DA actuator with DA valve
RA actuator with RA valve
NC (normally closed)
Spring closes valve
Valve fails closed
Valve and actuator have opposite action
RA actuator with DA valve
DA actuator with RA valve
RA/DA.With valves the normal/failed position will depend on the actuator and valve config. Either can be DA or RA
Fig Net effect of various combinations for two port valves (Arrangement of spring/diaphragm/port/valve seat dictates RA or DA action):

31. Pneumatic Valve Actuators
Close off issue (use these to make sure the valve can close against working pressure):
Air pressure x diaphragm surface area = force
Fluid pressure x valve seat area = force
Work with manufacturer application engineers, especially when actuator not supplied with valve
Use information here to help purchase a valve

32. Pneumatic Valve Actuators
Positive Pilot Positioners
Actual position of controlled device might not correspond to signal expectations
Friction, binding, aging, corrosion, spring range drift, etc
Amplifier/relay that corrects for the above
Moves valve to desired position if valve position does not match signal

33. Pneumatic Damper Actuators
Functions:
Open/close
Vary flow
Hold position
Meet sequences
Provide min/max range
Provide feedback
NO/NC is dependent on push rod linkage arrangement (linkage that connects damper to actuator)

34. Pneumatic to Electric - Converter
E/P Switch
P/E Switch
Interface the old pneumatics to the new electrical controls
Early steps towards Direct Digital Control Systems (DDC)

35. Self Acting Controls Self powered Two types
Liquid
Liquid expands when heated and contracts when cooled
This expansion/contraction force can move a valve or damper
Liquid/Vapor
Liquid boils to vapor when heated. Vapor condenses to liquid when cooled
Pressure difference when liquid or vapor causes force to act on valve or damper
See the following web site for details / pictures (reference materials):

36. Electric Controls Usually 24 volts AC
Use contact closures and resistance for control logic
Usually 2 position with the controlled variable sensed and compared to set point
Contact opened or closed accordingly

37. 2 Position Electric Controls
~<1hp, line thermostat used
~>1hp, motor starter with overload protection used
Traditional packaged HVAC systems used electric controls
Newer systems include analog/digital controls

38. Packaged HVAC Electric Controls: “Residential” Thermostat Wiring
Residential style Thermostats
Anyone know wires / colors / what they represent?

39. Packaged HVAC Electric Controls: “Residential” Thermostat Wiring
5 wire cable
Color
Terminal Code
Notes
1 24 VAC
Red R
Power
2 Heat
White
W or W1
Shorting (connecting) red/white = heat
3 Fan
Green G
Shorting (connecting) red/green = fan
4 Cool
Yellow
Y or Y1
Shorting (connecting) red/yellow = cool
5 Common
Blue C
Used in newer systems to power tstat (backlight , etc)
>5 wires multistage
Color
Terminal Code
Notes
6 2nd stage Cool
Light Blue Y2
7 2nd stage Heat
Brown R2
Potential activity and video:

40. Packaged HVAC Electric Controls
Wire coming to the RH, RC, or R terminal  - usually red - The red wire is the source hot wire from the transformer on the heating/cooling equipment. 
Wire coming to the G terminal - usually Green.  This is the fan relay - when energized, it will turn on the system fan/blower.
Wiring coming to the Y terminal - usually Yellow.  This is the compressor relay for cooling.  When energized, it will turn on the AC.
Wire coming to the W terminal - usually White.  This is the heating relay. When energized, the heating system will start up
Wire coming to the C terminal - usually Blue. This is power to the thermostat to do things like lighting the display, closing switching relays, keeping the program.
Without 5th blue wire, you will need a battery powered thermostat. 

41. Electric Actuators Types Linkage Configuration
Solenoid – 2 position
Motor – 2 position or modulating control
Linkage Configuration
Direct coupled – no linkages
Foot mounted – linkages
Normal or Failed Configuration
Spring return or fail safe
Non spring return
Motion
Rotary
Linear

42. DDC
The automated control of a condition or process by a digital device (computer)
Control energy costs with advanced programming and scheduling of equipment
Fault detection and alarming
Programming / graphical interfaces
Less maintenance than pneumatics
A DDC system cannot overcome design problems

43. DDC Control System PC Based DDC Control System Trunk / Network Cable
Field
Panel 1
Field
Panel 2
Field
Panel 3
LAN Devices
LAN Devices

44. DDC Controls operated by a digital microcomputer
4 types of control points (I/O)
Digital Points are 2 state (on/off, open/closed)
DI-Digital Inputs
DO-Digital Outputs
Analog Points have more than 2 positions (are variable)
AI-Analog Inputs
AO-Analog Outputs
A/D Converters – convert Analog values to Digital

45. Distributed Digital Controls (DDC)
Integrates controls
Enables central station monitoring
Enables more sophistical controls programming -- “algorithmic”
But still based on concept of Sequences of Operation!

46. Sequences of Operation

47. Control Strategies
A method for optimizing the control of building system equipment. The optimum outcome
What is an optimum control strategy?
One that does the following:
Fulfill sequence of operation
Minimize energy use
Minimize manual interaction
Minimize equipment wear and tear

48. Examples of Control Strategies
Set point control
Example - controlling room temperature to desired value (set point) using a thermostat and reheat valve
Lead / Lag control
Example – equalize run time by controlling which pump to bring on (lead) and which is on standby (lag) based on run hours

49. Control Logic
Control logic is portion of controller that produces outputs based on inputs
Algorithm: sequence of instructions for producing the optimal results to a problem
Control loop: continuous repetition of the control logic decisions
Open
No feedback
Closed
Feedback

50. Example SOP: Single Zone System
SPACE ZT EA NC RA NO OA MA H C C NC OA
EA-Exhaust Air
OA-Outside Air
RA-Return Air
HC-Heating Coil
CC-Cooling Coil
CD-Actuator
ZT-Zone temperature Sensor
NO-Normally Open
NC-Normally Closed NO NC CD CD

51. Example Partial SOP: Single Zone System
The hot water valve shall modulate to control a zone air temperature of 70 F. +/- 2 F.
The chilled water valve shall modulate to control a zone air temperature of 76 F. +/- 2 F.
The mixed air dampers shall modulate to control a mixed air temperature set point which is reset based on the zone temperature. The OA dampers will close on fan shut down. The OA dampers shall maintain 20% OA when the building is occupied. The OA dampers shall maintain minimum (occupied) or bypass minimum (unoccupied.) when the OA temperature exceeds 68 F. with a 2 F. differential.
The supply fan runs based on a time schedule. During unoccupied periods, fans will run when space temperature drops below 60 F. or rises above 85 F(with 3 F. differential) .
The return fan runs when the supply fan runs.

52. Maintenance of Controls

53. Maintenance of Controls
What kind of maintenance?
Calibration of sensors
Check and adjust actuators
Check schedules and set-points
Up-grades (usually programming)
Maintain documentation

54. Ideas for Controls Maintenance
Test safety devices & sequences
Inspect panels. Keep clean and dry.
Replace panel & wireless device batteries.
Inspect components. Test drive.
OA Dampers required
Update documentation (SOP’s, wiring diagrams, panel layouts, point lists, device literature, warranty info)

55. Ideas for Controls Maintenance
Calibrations
Examples of sensors that need to be calibrated periodically (usually code requirement): CO, CO2, OA Flow Meters, Refrigeration Detectors
Check sensor calibrations and replace if not accurate
Trends
Check for hunting (when controlled device constantly modulating excessively and never getting to set point), response to upsets, etc.
Ensure modes and sequences (Start up mode, shut down mode, cooling sequences, heating sequences ) are working
If DDC, review system activity logs of what has happened
Look for excessive alarms

56. Ideas for DDC Controls Maintenance
Your controller company could perform the following types of maintenance
Overrides
Failed Points
Alarms
Respond to legitimate
Clean up nuisance
Set up remote notification
Network diagnostics
Database/program back up
Get training from controller company

57. Ideas for DDC Controls Maintenance
Application Software upgrades
Operating System Upgrades
IT Maintenance: Security, etc
Panel firmware upgrades
Panel upgrades (hopefully backwards compatible, meaning that new controller can use old controllers programming and other features)
Remote access configuration
Portable device access configuration
Maintain response times / refresh rates

58. DDC Controls Maintenance – Network / Software Performance Benchmarks
Ensure system is not “slowing down”
Ways to define/track system speed (i.e. “why computer is so slow?”)
Graphic Display: Display graphic with minimum 20 dynamic points with current data within 10 seconds.
Graphic Refresh: Update graphic with minimum 20 dynamic points with current data within 8 seconds.
Object Command: Reaction time of less than two seconds between operator command of a binary object and device reaction.
Object Scan: Transmit change of state and change of analog values to control units or workstation within six seconds.
Alarm Response Time: Annunciate alarm at workstation within 45 seconds.
Multiple workstations: must receive alarms within five seconds of each other.
Program Execution Frequency: Run capability of applications as often as five seconds, but selected consistent with mechanical process under control.
Performance: Programmable controllers shall execute DDC PID control loops, and scan and update process values and outputs at least once per second.

59. Class Review and Reading Assignment
How Air Moves
Ventilation Rates
Air-Side Mechanical Systems and Components
HVAC Conservation
For next class, read BOC 103 (pp )
You can save energy by:
Establishing a “Dead-Band” Set-Point.
Using Air-side Economizer Mode (Free Cooling)
Night Purging
Utilizing an optimized Start and Stop
Decreasing Fan Speed
Consistently maintaining your HVAC system