pay now or pay forever - bcxa · pay now or pay forever commissioning the design of control system...
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Pay Now or Pay ForeverPay Now or Pay ForeverCommissioning the Design of Control System SoftwareCommissioning the Design of Control System Software
Bill GnerreInterval Data Systems
May 2, 2007
The Classic StruggleThe Classic Struggle
ConstructionFirst costDesign it rightPay now
OperationsLifetime costFix it laterPay forever
Case Study BackgroundCase Study Background
University business school building110K sqft3 AHUs218 VAVs
All with reheatSome fan powered
Central plant provides chilled water & steamJCI Metasys with 8,150 points
Good Intent, Bad DesignGood Intent, Bad Design
43%40%
17%
Control design intent issues
Control operator errors
Controls implementation issues
Software Software ≠≠ HardwareHardware
Hardware Hardware Hardware Hardware
Hardware
& Software Hardware
& Software Software Software
Example: WarmExample: Warm--Up ControlUp Control
Morning warmup sequence will be performed based on the lowest room temperature served by this air handler. The AHU will be commanded into “morning warmup” up to an hour (adjustable) before the scheduled occupied time is to occur. The amount of time the unit will be in “morning warmup” will be based on how far the lowest zone temperature is away from 68 degf. That amount of time will be based on the following table.
64 zone temperature (adjustable in GPL) 60 minutes (adjustable in GPL)68 zone temperature (adjustable in GPL) 0 minutes (adjustable in GPL)
The following will occur when unit is commanded into “morning Warmup”• The Differential CFM between the supply & return fan will be adjusted to 0 CFM.• The mixed air dampers will go to 0% ODA.• The supply air setpoint will be adjusted to 95 degf (adjustable).• Morning warmup will end if the unit is commanded into the occupied mode or if
the zone temperature reaches its target setpoint (adjustable).
Morning warmup sequence will be performed based on the lowest room temperature served by this air handler. The AHU will be commanded into “morning warmup” up to an hour (adjustable) before the scheduled occupied time is to occur. The amount of time the unit will be in “morning warmup” will be based on how far the lowest zone temperature is away from 68 degf. That amount of time will be based on the following table.
64 zone temperature (adjustable in GPL) 60 minutes (adjustable in GPL)68 zone temperature (adjustable in GPL) 0 minutes (adjustable in GPL)
The following will occur when unit is commanded into “morning Warmup”• The Differential CFM between the supply & return fan will be adjusted to 0 CFM.• The mixed air dampers will go to 0% ODA.• The supply air setpoint will be adjusted to 95 degf (adjustable).• Morning warmup will end if the unit is commanded into the occupied mode or if
the zone temperature reaches its target setpoint (adjustable).
Example: WarmExample: Warm--Up ControlUp Control
Warm-up command triggered off one of few rooms below setpoint
Room temps rise to 80°+ as VAVs try to cool with
hot air
Warm-up command setpoint
AHU increases supply air temp to mid-90°s, but
does not tell VAVs that warm-up is in progress
A PandemicA Pandemic
Issues like these exist everywhere
An Operational Design Specification An Operational Design Specification
“Design is not just what it looks like and feels like. Design is how it works.”
– Steve Jobs
An Operational Design Specification An Operational Design Specification
Goals for specification:Minimize the mystery Minimize technical jargonDefine integration detailsDescribe facilities’ business obligations Provide integrated organizational approachAddress cultural barriers
An Operational Design Specification An Operational Design Specification
Goals for building/operations:
1. Achieve comfort and IAQ in every space
2. Meet #1 at the lowest possible cost
3. Operate automatically, without operator assistance, 24x365
Anatomy of an Operational SpecAnatomy of an Operational Spec
Six main sections:PhilosophyComfort / IAQHardwarePointsControl strategiesAcceptance
PhilosophyPhilosophy
Overview of approachNon-technical and technical audienceFramework for rest of specification
Comfort / IAQComfort / IAQ
Define comfort & IAQ requirements in non-ambiguous termsASHRAE standards
55-200462.1-2004
Methodology for measurement
Hardware Hardware
Sensors SelectionLocation Calibration
Explain the need/value of each sensor
PointsPoints
Name standardizationList points to be exposed and why
Expose points for operatorsExpose points for data collection/historical recordCollection intervalPoints used for calculations
Control Control Strategies Strategies
Detailed spec for software programs
PredictableRepeatable
Identify all points of integrationLogic diagrams with English descriptionsTied to specific hardware selection
AcceptanceAcceptance
Assure system meets customer obligationsVerify operations, not a hardware functional test
Space conditionsComponent operationsSystem-level (integration) operations
Operations ManualOperations Manual
Train operatorsHow system works (not just howindividual components work)How to address issues/complaints
Reduce/eliminate the 17% self-inflicted errorsIncrease persistence
17%
Control operator errors
ConclusionsConclusions
Software is a critical component of control systemsSeparate from hardwareRequires its own specification
Must improve over typical sequence of operations to ensure predictable, repeatable resultOpportunity exists for design stage CxChallenge exists to deal with sophisticated software design and developmentWe must get the software right before DDC will finally deliver on its potential
