Building Operator

Certification –Level I

A Partnership of the CUNY Institute for Urban Systems

Building Performance Lab, the CUNY School of Professional

Studies, and the New York State Energy Research & Development

Authority

Building Operator Certification Level I (BOCI)Building Systems: HVAC Systems

CUNY School of Professional Studies

CUNY Building Performance Lab

The BOC

Control Principles, Terms and Concepts Lesson 10

> 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)

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

Control AcronymsATC – 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

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.

Control Concepts – More TermsControl 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.

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

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

2 Position ControlDigital (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 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.

Modulating ControlPID 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

Proportional Only ControlSimple / 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

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.

Proportional plus Integral (PI) ControlAn 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.

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.)

Types of Controls and Control SystemsClassified by Energy Sources:

Pneumatic

-Self Acting

-Electric

-Distributed Digital Control (DDC)

Pneumatic ControlsPowered 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)

Pneumatic System Diagram

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

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)

Example of Pneumatic ActionDirect 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

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

Pneumatic ThermostatsDay/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

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.

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

Pneumatic Control Valves

Diaphragm

DIAPHRAGM

Pneumatic Valve ActuatorsNO (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

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

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)

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

Self Acting ControlsSelf 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):> http://www.spiraxsarco.com/resources/steam-engineering-

tutorials/control-hardware-sa-actuation/self-acting-temperature-controls.asp

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

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

Packaged HVAC Electric Controls: “Residential” Thermostat Wiring

Residential style Thermostats> Anyone know wires / colors / what they represent?

Packaged HVAC Electric Controls: “Residential” Thermostat Wiring5 wire cable Color Terminal

CodeNotes

1 24 VAC Red R Power2 Heat White W or W1 Shorting (connecting) red/white =

heat3 Fan Green G Shorting (connecting) red/green =

fan4 Cool Yellow Y or Y1 Shorting (connecting) red/yellow =

cool5 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

Packaged HVAC Electric ControlsWire 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.

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

Maintenance of ControlsWhat kind of maintenance?

Calibration of sensors

Check and adjust actuators

Check schedules and set-points

Up-grades (usually programming) > Maintain documentation

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

DDC Control System

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

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!

Ideas for DDC Controls MaintenanceYour 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

Ideas for DDC Controls MaintenanceApplication 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

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.

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

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

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

Example SOP: Single Zone System

H

C

C

CNC

NO

RA

OA

OA MA

SPACEZT

EA NC

CD

NO

CD

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

NO-Normally OpenNC-Normally Closed

Example Partial SOP: Single Zone SystemThe 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.

Ideas for Controls MaintenanceCalibrations

> 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

Class Review and Reading Assignment

> How Air Moves> Ventilation Rates> Air-Side Mechanical Systems and Components> HVAC Conservation

NEW MODULE (Classes 11-15): Energy DataRead FEMP Chap. 8Herzog, Chaps. 1 & 2