Modeling

It’s not Just for Calendars and Energy

Nathan KegelASHRAE Member, LEED AP BD+C

Project Manager

Business Development Manager

Nathan.kegel@iesve.com

www.iesve.com

Learning Objectives:• Understand What a Model Is• Understand Different Types of Models for

Buildings• Understand the difference between BIM and

BAM and how to use them in practice• Understand traditional, current, and potential

future best practices for building modeling• Understand the value of a model for new and

existing buildings• Introduce alternatives to ASHRAE 90.1

What’s a Model?

A MODEL is a device or structure that helps us:• Understand the world around us• Understand a piece of the world around us• A simplified representation of our surroundings

in order that we may pursue understanding

Modeling Mindset

“… we must pursue understanding .Not answers but understanding .”

Bellinger G. (2004) “Simulation is not the Answer”

Modeling Mindset

“Everything should be made as simple as possible, but not simpler.”

Modeling Mindset

“Obstacles are those frightening things you see when you take your eyes off goals.”

“Whether you think you can or think you can’t, you’re right.”

Building Modeling : BIM and BAM

BIM: Building Information Model• Building Information• Uses include construction documents, clash detection &

constructability, cost estimating, scheduling, etc.

BAM: Building Analytical Model• Building Analysis• Uses include climate modeling, thermal loads modeling,

structural loads modeling, daylight modeling, thermal comfort modeling, airflow modeling, temperature modeling, energy modeling, solar modeling, performance optimization, life cycle cost assesment, etc.

Building Analytical Modeling – Beyond Energy

Daylight Model

Airflow (CFD) Model Thermal Loads Model

Solar penetration Daylight levels Natural Ventilation

Results color coded on model Daylight Metrics Climate Understanding

J J A S OJ F M A M N DCopyright © 2008 Integrated Environmental So lutions Limited. All rights reserved

Monthly Energy Output * Daylight contours A nnual Energy Output *

BAM: Some more examples

Models for Buildings – Traditional Practice

Multiple Models for Multiple PurposesCAD/BIM for construction; HVAC loads, energy, daylight, solar, rendering, airflow, etc.

Thermal Loads Solar Airflow (CFD) Energy Ventilation

Daylight Rendering Artificial Light LEED Code Compliance

Traditional Practice - Benefits

1. It’s “familiar”• Meaning Comfortable• “What we’ve always done”

1. It’s “familiar”• Meaning Limited & Inefficient

2. Lots (and lots) of repeated work• AKA - Inefficient

3. Lots (and lots) of loopbacks4. Lack of Data Integrity

• Accuracy and QA can easily suffer leading to higher chance for GIGO or incomparable results

Traditional Practice - Drawbacks

Models for Buildings

Possible in Today’s Practice:Fewer Models serving Multiple Purposes:CAD/BIM for construction plus an Analytical Model studying thermal, energy, daylight, solar, airflow, comfort, etc.

Building Analytical Model

Today’s Best Practice - Benefits1. It’s not familiar

• Meaning innovative2. Less data entry

• More time finding best solutions3. Fewer loopbacks

• More efficient4. Lower chance for GIGO

• Fewer datasets to manage and QC

1. It’s not familiar• Meaning there is a learning curve• Innovation might be frightening to some• Initial investment period before efficiency is

realized

Today’s Best Practice - Drawbacks

Today’s Best Practice – Truly Informed Design

Analysis Informs Design

Models for BuildingsIdeal Practice?: 1 Building, 1 Model

Ideal Practice? - Benefits1. Minimal re-work

• Best efficiency2. Potential for minimal GIGO

• More time finding best solutions3. Fewer loopbacks

• More efficient4. Parametric

• When one thing changes, other related items automatically update

1. Karoshi2. Who manages what?

• For example, is the architect now responsible for the quality of the thermal model?

• GIGO potentially bigger problem if not caught early on and managed properly

3. Too much detail – leads to instability and uncertainty in analysis

4. Parametric – Is it now just a “black box”?

Ideal Practice? - Drawbacks

Measures of Quantity – BIM

Measures of Quantity – Project Delivery

Measures of Quality – Daylight Analysis

SC = 0.6VLT = 75%

SC = 0.2VLT = 35%

Daylighting Quality Exterior Tint

Understanding Visual Quality - Glazing Options

Lighting & Daylighting

No Solar Shading

With Solar Shading

• Will glare be problematic late in the day?

• How Effective is the External (or Internal) Shade at reducing Glare?

Understanding Quality - Glare & Solar Shades

Building self-shading through brise soleil Building self-shading

Shading from adjacent buildingsUnexpected mid-evening peak

cooling load on east façade?

Summer sun Winter

sun

Understanding Solar Analysis

Infiltration heat loss can account for

up to 40-50% of a building’s Heating

Load....

...Building Pressure Tests

0 2000 4000 6000 8000 10000 12000 14000

Heating Load (Btu/h)

Fabric Loss

Infiltration Loss

Understanding Quality of Envelope - Dynamic Infiltra tion

Understanding Quality - Airflow (CFD )

Understanding Quality - Building Performance

Compliance With Codes & Rating Systems

BAM: Value to Existing Buildings

• Predict energy use, costs during operation• Calibrate energy model per

utility bills or building performance• Sensitivity Factors

• Calibration methods, tools• Data collection• Utility rates

The Future: Smart Buildings• Continuous Calibration to

Optimize Performance• Anticipate problems on the

fly using trended data• Reduce Total Cost of

Energy and Improve Occupant Comfort

• Detailed Analysis Models will be the heart– Note: +/- 10% is NOT good

enough– Note: “Fudging factors” will

not work for Smart Buildings

• Cost of calibrated models• Construction QA practices lacking• Cheap Energy & Current Financial Metrics• Lack of accurate data• Lack of enough detailed data• “Fudge Factors” are still common practice• ASHRAE 90.1 Mindset

Current Challenges

ASHRAE 90.1 – 2010• Prescriptive Path

– Prescriptive Path encourages building the worst possible “legal” building; it does not encourage building the best possible building

– There are no requirements for testing or QA during construction and occupancy

• Performance Path (Appendix G “Baseline”)– There is no actual baseline in Appendix G– Appendix G does not allow for certain measures to be included

• For example, reduction in OA by using a system type which delivers OA more efficiently

– There are no requirements for testing or QA during construction and occupancy

• Benchmark versus Goal– Benchmarks measure against current state; not against desired state– Goals identify desired state; current state is less important

• Incredibly Complex– Creates confusion in the marketplace– Practitioners often spend more time on the baseline than on improving the

proposed building• “Fudge Factors” are allowed – some even specified in Appendix G

ASHRAE 90.1 – 2010New Appendix G requirements

• Accounting for Site Conditions– Theory: Buildings aren’t built in a vacuum and site conditions do matter– Practice: Poor implementation of this theory leads to more confusion & inaccuracies

• 90.1-2010 allows for site impacts that are physically impossible• 90.1-2010 has exceptions which allow some software modeling tools to easily fake results

• Minimum requirements for HVAC efficiencies improved– Baselines are (theoretically) more efficient– Proposed case does not require modeling tools to accurately model actual HVAC

systems• Convoluted (and frequently inaccurate) workarounds are still permitted

• Envelope requirements require more insulation for certain climate zones– Meaning theoretical worst possible building is theoretically slightly better– Mass factors still allowed – meaning detailed accounting of thermal mass impacts is

NOT REQUIRED

• Incredibly Complex– 2010 version got more complex, not less– Practitioners often spend more time on the baseline than on improving the proposed

building – this will probably get worse instead of better

• “Fudge Factors” are allowed – some even specified in Appendix G

ASHRAE 90.1 – 2010Detailed Solar for the Appendix G Baseline & Propos ed Cases

• Some obvious questions here:– If the simulation program cannot simulate shading by adjacent structures,

how can it tell you which surfaces are shaded “most of the time”? Hence, how can you determine which surfaces should be modeled as north-facing?

– What about urban areas? Rotation of baseline and proposed with site will cause physical impossibilities.

Building self-shading

Self Shading Still not Required in 90.1

Problems with Building Only Rotation

ASHRAE 90.1 – 20100-degree Solar for the Appendix G Baseline & Propos ed Cases

ASHRAE 90.1 – 2010180-degree Solar for the Appendix G Baseline & Prop osed Cases

Alternatives: Moving Beyond Benchmarks• A new paradigm:

– Require design and construction teams build and design the best possible building

– What is the best possible building?• Net Zero Energy

• New York

• Wisconsin

• Hawaii

Net Zero Energy is the Index• Projects already constructed which achieve this standard• Penalizes waste and encourages best possible building• Simplifies the modeling process• Encourages teams to seek best possible solutions, not just minimums• More time available to explore best alternatives rather than spending

excessive amounts of time struggling with theoretical baselines• Promotes understanding• Promotes changes to occupant behavior• Changes the financial model for implementing renewables• Grows several segments in the economy

– Energy Modeling– Renewable Energy– Construction (renovation and new)– Generates a revenue source for new research

• Funded by the biggest energy users

• More efficient use of resources– Human– Renewable– Non-renewable