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Modeling Building Services Equipment: Getting Beyond Ratings and Default
Curves
Charles S. Barnaby
15 November 2017
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The Issue
Equipment performance ratings are central to energy regulations.
Ratings do not provide sufficient information for detailed simulation.
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Apologies for Perspective
U.S. examples
I-P units
Residential (-ish)
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Hemispheric Dissonance
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New Hampshire (46.7 °N)
Yesterday
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Talk
Ratings and their discontents
Detailed equipment performance data availability
Consensus standards (e.g. ASHRAE Std 205P)
Recommendations
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Equipment Ratings
Single/few value(s) to characterize performance (e.g. energy efficiency)Examples
HSPF = Heating Seasonal Performance FactorIEER = Integrated Energy Efficiency Ratio
General guidanceDeveloped w/o consideration of detailed simulation
→ Unhelpful for simulation
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Ratings Swamp
Tempting to reverse-engineer. But …
Round-off– 6.1.2 Values of Measures of Energy Efficiency. Standard measures of energy
efficiency, whenever published, shall be expressed in multiples of the nearest 0.05 Btu/Wh for EER, SEER and HSPF, and in multiples of 0.1 for IEER.
Stepped values– Design load used in HSPF calculation is stepped in 5,000 or 10,000 Btuh
increments based on unit capacity.
Auxiliaries– Crankcase heater can use more energy than compressor
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Ratings More Swamp
Artificial rating conditions– Variable-speed compressor rated at full speed but full speed not used
in the field
Multiple/expensive/complex defining standards– Simulation use case not considered
– Application difficult even if possible
Not unique– Same rating / different performance
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What About Rating Precursors?
Can do better if test results are known– Heat pump: low/high temp capacity and efficiency
But still problems– Ever-increasing heat pump capacity at low temperatures
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Ratings Not Unique
If regulations or baselines are based on ratings, what do we simulate?
Reference equipment must be defined
• Not recognized task
• Not easy
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Reference Equipment
Methods that have been attempted …• Selection by expert
• Regression
• Generation of subcomponents
• Runtime adjustment factors
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What Do Models Need?
Correlations (aka curves)• EnergyPlus, DOE-2, …
Performance maps
• TRNSYS, EnergyPlus (?), ESP-r, …
Sources• Big jobs (= chillers) – get data, fit curves• Small (= residential) – use defaults
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Data Example
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It Gets WorseSoftware input formats differ
– Multiple tools / same equipment, please start over!
Ever more tools
Ever more analysis requirements– Codes
– Asset ratings
– LEED / Standard 90
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Why Is Performance Info Not Available?
We (modelers) have complained for 40 years.
Some barriers --• Manufacturers do not understand our requirements• Manufacturer resource limitations• Manufacturers do not know• Manufacturer proprietary concerns
We are to blame – we never really asked!
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Make a StandardConvene stakeholders• Data publishers (manufacturers)• Software developers• Other organizations• Software users
Agree on data formats• Publishers agree to use formats• Software developers agree to implement ability to read
formats
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Standard 205P
Title
Standard Representation of Performance Simulation Data for HVAC&R and Other Facility Equipment
Purpose
To facilitate sharing of equipment characteristics for performance simulation by defining standard representations such as data models, data formats, and automation interfaces.
Scope
This standard applies to data used in the performance simulation of any HVAC&R or other facility system, equipment, or component.
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Approaches
Many ways to solve the problem• Data
• Coefficients (“curves”)
• “Active elements” (scripts, DLLs, …)
Hence general term “Representation”
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Representation AlternativesPerformance map (“just data”)
Pro: Model neutral, simplicity, arbitrary detailCon: Bloat, inconvenient to use (complex interpolation)
Coefficients (EnergyPlus, DOE-2, )Pro: Directly usable (or not), compactCon: Publisher must derive, software specific, implicit model form
Active elements (scripts, DLLs, FMU, )Pro: Arbitrary detail, compactCon: Black box
Standard 205P: Performance maps
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How to Standardize
“Just” agree on names, definitions, units, and precision for all items.
Std 205P approach –Standard body: common requirements (naming conventions, units, …)Appendices: Representation Specifications• Liquid-Cooled Chiller• Unitary Cooling Air-Conditioning Equipment• Fan Assembly
6 years later …
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Example Requirements
NamesConsensus: clarity trumps brevity
Long(ish) / self-documenting – “airVolumeFlowRate”
UnitsConsensus: dual units = publication burden / ambiguity
SI only
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Representation SpecificationHuman-readable (PDF) document that defines what is in a representationData publisher: how to export
Application developer: how to import
User: Understanding of data
Typical contentDevice diagram
Data element definitions
Validity rules
References
Supporting discussion
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Representation
Machine readable (= file)Identification, general info, ratings
Performance data• Performance Map: collection of Performance Points (= multi-dimensional
hyper-rectangle)
• Performance Point: set of conditions + capacity, input power, …
• Multiple performance maps for modes (operating, standby, …)
• Operational limits: tag points as non-operating
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Validity
How can data be wrong?
Good faith• Measurement errors, typos, bugs, …• Response: QA rules (range checks, physical consistency, …)
Bad faith• Fraud, counterfeit info• Response: digital signatures?
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Other Issues
Access control• Info may be proprietary
• Response: encryption OK
Revision• Info change: Corrections, product enhancements
• Standard change: Corrections, improvements
• Response: strict version identification
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Implementation
File format• Initial thought = XML – however, too verbose
• Looked at JSON, YAML, …
• Current experiments using Google Flatbuffershttp://google.github.io/flatbuffers/
Considering open-source support libraries (interpolation, validation, …)
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Standard 205P Status
Advisory public review complete Oct 31• 3 initial equipment types• Full public review early 2018?
Additional components• VRF• Cooling towers• Fan coils• Heat pumps• Water heaters?• Windows?
Please get involved!
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What About Controls?
Performance maps can capture some features
Component-level controls often implicit in software, details not accessible
Proprietary and ever-changing
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Recommendations
Convey to regulators that ratings are not sufficient
– Define reference equipment
Continue standard development such as ASHRAE 205
Promote international harmonization of standards
Promote open-source software to support standards
Promote public availability of standards
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Thank you!
Questions?
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