Modeling Building Services Equipment: Getting Beyond Ratings and Default

Curves

Charles S. Barnaby

15 November 2017

15 November 2017 2

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

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

Productive workflow essential15 November 2017 15

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

15 November 2017 30

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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