Building Systems and Performance: an

Introduction to Building Operator

Certification –

Lesson 10: Control Principles, Terms,

and Concepts

CUNY Institute for Urban Systems Building Performance Lab

Lesson 9 Review

Control Principles, Terms, and Concepts Agenda

• Control principles, terminology and concepts.

• Types of controls and control systems.• Sequences of operation.• Maintenance of Controls.

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)

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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

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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

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Control Concepts - TerminologyControlled 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.

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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.

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Control Loops

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

Closed Loop Control • Thermostat for room temperature• Boiler Pressure Control• Lighting Level Control with Dimming

sensor controller controlled variable

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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

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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• Freeze stats• Moderate to slow responding control loops• Step Control: Multi speed motors, multi stage burners, multi

stage compressors

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Two Position ControlAn 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.

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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

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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

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Proportional (P) ControlAn 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.

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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.

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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.)

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Types of Controls and Control Systems

• Classified by Energy Sources:

• Pneumatic• Self Acting

• Electric

• Distributed Digital Control (DDC)

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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)

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Pneumatic System Diagram20

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

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Pneumatic Thermostat

• 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)

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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

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Pneumatic Thermostat Action

Air pressure is fallingTemperature is falling Direct acting

Air pressure is risingTemperature is rising Direct acting

Air pressure is fallingTemperature is rising Reverse acting

Air pressure is risingTemperature is falling Reverse acting

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Pneumatic Thermostats• Day/Night Set Points

• Heat/Cool Set Points

• Different manufacturers use different pressures:Mfr Day (psi) Night

(psi)Honeywell 13 18Johnson 15 20Siemens 18 25Barber Coleman

15 20

Robertshaw 16 25

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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.

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Pneumatic ActuatorsRequired air pressure is determined via spring range.

• Honeywell book pages 74 and 75: Figures 26 & 27:

• http://customer.honeywell.com/techlit/pdf/77-0000s/77-E1100.pdf

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Pneumatic Control Valves

Diaphragm

DIAPHRAGM

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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

Fig. 6.6.5 Net effect of various combinations for two port valves (Arrangement of spring/diaphragm/port/valve seat dictates RA or DA action):

http://www.spiraxsarco.com/resources/steam-engineering-tutorials/control-hardware-el-pn-actuation/control-valve-actuators-and-positioners.asp

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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

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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)

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E/P Switch

Interface the old pneumatics to the new electrical controls

Early steps towards Direct Digital Control Systems (DDC)

Pneumatic to Electric - ConverterP/E Switch

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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

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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

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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

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Packaged HVAC Electric Controls: “Residential” Thermostat Wiring

• Residential style Thermostats• Anyone know wires / colors / what they

represent?

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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: http://www.prothermostats.com/find_thermostat.php

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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.

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Electric Actuators

• Types• 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

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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

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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

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DDC Control System42

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

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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!

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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

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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

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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.

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Sequences of Operation: 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

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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

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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

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Example SOP: Single Zone System

H

C

C

CNC

NO

RA

OA

OA MA

SPACEZT

EA NC

CD

NO

CD

NC

EA- Exhaust AirOA- Outside AirRA- Return AirHC- Heating CoilCC- Cooling CoilCD- ActuatorZT- Zone temperature Sensor

NO-Normally OpenNC-Normally Closed

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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.

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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 modulates excessively, 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

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Class Review and Reading Assignment

Today’s topics:• How Air Moves• Ventilation Rates• Air-Side Mechanical Systems and Components• HVAC Conservation

Readings for next class:• Read FEMP Chap. 8 (METERING FOR O&M)• Herzog, Chaps. 1 & 2

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