Ryan R. Hoger,
LEED AP
Building Automation Systems z z z z z z z
Centralized controls
Change scheduling for multiple
HVAC units at same time
Monitor “health” of equipment
Internet accessible
Alarming via text msg or email
Collect/trend data
Integrate to lighting control or security system
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3/11/2013 z DDC Direct Digital Control of an HVAC system z A method of monitoring and controlling
HVAC system performance by collecting, processing, and sending information using sensors, actuators, and microprocessors.
What is DDC?
z DDC is the concept or theory of HVAC system control that uses digital controls z Physically, DDC encompasses all the devices used to implement this control method: a whole group of DDC controllers/microprocessors, actuators, sensors, and other devices.
What is DDC?
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DDC - the Control
Theory input-process-output cycle z A point is ANY input or output device used to control the overall or specific performance of equipment or output devices related to the equipment.
What Is a Point?
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AI z
DI z
AO z
DO z
Analog input - a sensor that monitors physical data, such as temperature, flow, or pressure.
Discrete input - a sensor that monitors status .
Momentary and maintained switches, ON-OFF equipment status, and digital pulses from flow and electric power meters are discrete inputs.
Analog output - a physical action of a proportional device in the controlled equipment - e.g., actuator opens air damper from 20% to 40%, other dampers, valves, inlet guide vanes, etc.
Discrete output - changes or maintains device status. Performs momentary or maintained switching for start/stop of pumps, fans, two-position dampers, and on/off control.
Four Kinds of Points
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Input sensors and status devices react to changes in conditions . Conditions include internal load, outside air temperature, and output actions .
Output devices act based on sensor and status device reactions .
Ex. 1:
Open cooling coil valve (output action). Supply air temperature sensor
SAT detects (input reaction) decrease in temperature.
Ex. 2:
Filters on an air handler get dirty (conditions). Air switch reacts by closing contact for “filter dirty” alarm.
DDC: Actions and Reactions
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Control Point
Identification Exercise
AI z z z z z z z Temperature
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Thermistors
Resistance Temp. Detectors
(RTDs)
Transmitters
Pressure
Humidity
Flow (CFM, GPM)
Voltage
Current
CO2
DI z z z
Switch dry contact
(open or closed)
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Airflow
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Water
Differential pressure
High/low limit switch
(alarm or normal)
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Freeze alarm
Smoke detectors
Wattmeter pulses
(pulse initiator or counter)
Sensor and Status Devices used as Input Points
(Reactions)
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AO z z z
Damper actuators
Modulating valves
VFD
DO z Solenoid valves z z
Relays / contactors
Alarm signal
Devices used as Output Points
(Actions)
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Closed Loop Control is accomplished by the control signal being sent to the controlled device with constant feedback from the sensor/status device providing input to the controller.
DDC: Closed Loop Control
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Closed loop control is determined by: z Control algorithms z Configuration values z Time schedule data z Setpoint schedule data
Closed Loop
Control
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Heating/cooling coil control
Humidification/dehumidification
Mixed air damper optimization
VAV fan control
VAV supply & return fan tracking
Indoor air quality
Generic PID control
Control point reset
Typical Control
Algorithms
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Time of day scheduling
Discrete device controlled as analog
Discrete interlock
Discrete staging
Proportional thermostat
Primary/secondary pump control
Night free cooling
Adaptable start/stop
Permissive interlock
Typical Control
Algorithms (cont’d)
P Proportional
PI Proportional-Integral
PID
Proportional-Integral-Derivative
Algorithm Type Used by
Processor Determines
Control Strategy
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PID =
Proportional-Integral-Derivative Control z z
What it is: This type of control algorithm is based on value/amount (proportion), rate of change (integral), and error allowances (derivative). PID control calculates and sends commands for outputs based on all three types of information.
Advantages: More precise than P and PI controls,
PID wastes less energy based on more frequent feedback and quicker responses.
What Is PID Control?
3/11/2013 z What it is: Control algorithm based only on value/amount (proportion). z Disadvantages: Less precise than PID and PI control; cannot respond to error margins or time. Uses the most energy due to over- and under- outputs.
Proportional Control (P)
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z z
What it is: Control algorithm based on value/amount
(proportion), rate of change (integral). PID uses error allowances (derivative) as well.
Advantages: More precise control and less energy used than proportional (P); minimum swings from setpoints.
Proportional-Integral Control (PI) &
(PID)
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Exercise 1: Base CV
Air Handler Unit -No
Controls
Exercise 1: AHU - DDC
Control of
Start / Stop
Scheduling
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Exercise 1: AHU - Add
DDC
Damper
Exercise 1: AHU - Add DDC
Cooling Coil
Control
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Exercise 1: AHU - Add DDC Outside Air reset and Enthalpy Control
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Control Point Summary for Base CV AHU
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z z
VAV systems came into favor for mid and large size facilities in the 1960s and 1970s
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Save energy
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Improve comfort
Take advantage of building diversity
Cooling needed year round for true interior core zones
Sequence
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Main AHU provides morning warm-up heat until RAT setpoint is satisfied – all zones at 100% design airflow
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AHU switches to 55°F discharge air controlled cooling – zones modulate CFM to controls space temp
No AHU heat remainder of day – individual zone reheat or baseboard as needed
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Heating/Cooling
Unit
ROOF
Heating/Cooling
Unit
Heating/Cooling
Unit
Heating/Cooling
Unit
TMT
ZONE 1 ZONE 2
TM
ZONE 3 ZONE 4
TM
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To Build DDC on a VAV AHU,
Start with DDC on a CV AHU...
Exercise 2: Create a VAV
AHU with Inlet Guide
* If using VFD, use two Variable Frequency Drives instead, but you will still need the same control points and HPS shown.
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• Filter Status (FLTS)
• FreezeStat (FRZ)
• Smoke Detector (SMK)
Typical DDC Items You Can Add as Optional Items:
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Exercise 2: VAV AHU with DDC Filter Status
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Exercise 2: VAV AHU with DDC
FreezeStat
Exercise 2: VAV AHU with DDC Smoke
Detector
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Programmable controllers
Application
Specific controllers
Control
Point
Summary for Base
VAV AHU
Factory integrated controllers
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Types of Direct Digital Control Networks z Interface - devices and software that work as a translator between a DDC system and the humans who operate it.
z An interface is the operator’s window into a building’s operating systems and conditions.
Interfaces to DDC
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User interfaces:
Allow more efficient system operation monitoring.
You can look at what’s happening on all floors from the tenth floor if DDC network is peer-to-peer.
• Allow immediate diagnosis of HVAC units and controls, including changes, without physically being in front of the unit.
• Can provide reports (e.g., historical, consumable, run times, system activity) to be used as records of building operations.
• Can provide graphical representations of the controlled system.
User Interface Benefits
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User Interface Types
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Hand-held Connected to a DDC Controller
Interface
Examples
PC Connected to a DDC Network
Interface
Examples
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Web Server Connected to DDC Network
Interface
Examples
z Standard web browser or WAP access z View system status z Access schedules and setpoints z z
Trending, alarming, reporting
Real time interactive graphics
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z Low cost alternative to
BAS z Direct to Ethernet z No PC software – uses standard web browser z No access fees z Text/email alerts
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z z z
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Add new HVAC equipment to an existing Building
Management System
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Lighting, HVAC, Security, Fire & Life Safety
Enterprise Integration-Utilities, Financial
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HVAC
Lighting
Security
Power
Metering
PT
PT
PT
MODBUS®
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Interoperability is the ability of different devices from the same or different manufacturers to function accurately together.
Standard protocol - a set of guidelines for commands, inputs, and output encoding to create a universal language for all DDC devices. When the same standard protocol is used in DDC devices, interoperability is possible.
Gateways - devices added to DDC networks to make standard protocols available and interoperability possible.
Interoperability
BACnet
Standard protocol requirements for B uilding A utomation and C ontrol net working, created by ASHRAE to ensure interoperability. BACnet uses software and a LAN interface to DDC to provide:
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Representation of all manufacturer devices’ internal functioning in a common, network-visible way.
A common command set for device services.
Common encoding of commands, understandable by all devices and interfaces adhering to the protocol.
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Enterprise
Security Systems
Energy
MODBUS
Lighting
Fire Systems
LEGACY
Open System
Framework
CFO
XML SQL
HTTP HTML
ODBC SNMP
Facility
Management
JDBC FTP
WAP
SMTP
HVAC Systems
And More
z z
Q: What part of the control system is done by the HVAC designer?
What is done by the installing contractor? Do most HVAC engineers actually do control system work or is that done by specialty contractors?
A: Depends on the project
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A good designer lays out the control system as an integral part of the mechanical system, including: z Sequence of operation z Front-end/user interface details
The details of hardware, software, and cabling should be left to the contractor since every manufacturer’s system is different
– Unfortunately, most designers rely on manufacturers to write project specs, or worse, contractors to design in the field as they install
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z z
Q: How does one select the type, number, and position of sensors? (i.e. measure temp in a room or in the supply duct? Where in the room or duct do the sensors go?
How many go in each room?)
A: Depends on the project
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Best to measure what you want to control – usually space temp z Mount between 4 and 5 ft high, out of direct sunlight, and in the return air path z One sensor per controllable piece of equipment is best – usually one per room
Many exceptions for specialty systems and/or install cost compromises
z z
Q: How does one go about determining the coefficients of a P, PI, or PID controller and tune the system once it has been installed?
A: Practice and Patience
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Zero out the derivative term – HVAC equipment and building systems react too slowly for it to matter
Tune the proportional term first, then worry about integral term
Make small changes and monitor
Use a dynamic graph
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z z
Q: Where can one go to get more information and training?
A:
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Iowa Energy Center / Iowa State University z www.ddc-online.org
ASHRAE Learning Institute z http://www.ashrae.org/education/page/1809
Continental Automated Buildings Association - www.caba.org
www.automatedbuildings.com
BACnet - www.bacnet.org
z z z
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352 HVAC units
311 guestrooms
Added DDC controls
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Occupancy sensors
Entrance door & motion
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Energy Savings Estimation Tools
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• Programmable Thermostat
• Nicor Gas or NIPSCO Gas – $50
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Peoples Gas or North Shore Gas – $80
Wisconsin Focus on Energy – $100 per RTU
• Economizer Controls
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ComEd – $40 per ton
Wisconsin Focus on Energy – $250 per RTU
• CO2-based DCV
• ComEd – $0.03 per ft2
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DCEO – $0.28 to 0.40 per ft2
Peoples Gas or North Shore Gas – double custom
NIPSCO Gas – $0.15 per ft2
Wisconsin Focus on Energy – $0.05/CFM supply
Wisconsin Focus on Energy – $350 per RTU
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• Boiler Reset Control
• Nicor Gas – $0.50 per MBH
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Peoples Gas or North Shore Gas – $500
NIPSCO Gas – $0.35 per MBH
Wisconsin Focus on Energy – $75/controller
• DDC Controls
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ComEd – $0.20 per ft2
DCEO – $0.20 to 0.40 per ft2
• Variable Frequency Drives (VFDs)
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ComEd – $60 per Hp
DCEO – $92 per Hp
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NIPSCO Electric - $40 per Hp
Wisconsin Focus on Energy – $50 per Hp
• Hotel Guest Room Energy Mgmt System
• ComEd – $25 to 65 per unit
• Kitchen Exhaust Demand Control Ventilation
• ComEd – $350 per Hp
• Custom Incentives (based on annual savings )
• ComEd – $0.06 to 0.07 per kWh
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Nicor Gas – $0.75 to 1.00 per therm
Peoples Gas or North Shore Gas – $1.00 per therm
DCEO – $0.12/kWh and $3.00/therm
NIPSCO – $0.09/kWh and $0.60/therm
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3/11/2013
Ryan R. Hoger,
LEED AP
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