Energy modelling is an important tool in the design of low energy buildings. It helps evaluate energy savings of various energy efficiency measures and can predict total building energy consumption.

1. Development of an Open Source Hourly
Building Energy Modeling Software Tool
! Brittany Hanam MASc EIT
! John Straube PhD P.Eng.
05/12/2011

2. Agenda
! Energy Modeling and Design
! A New Model
! Case Study

3. Building Energy Modeling
! An important tool in the design of low energy buildings
! Evaluate energy savings of various energy efficiency measures
! Predict total building energy consumption
! Show compliance with standards
! Determine peak loads, size equipment

4. Some Areas for Improvement
! Energy modeling for architects
! Architects’ design has a significant impact on energy
consumption but mechanical engineer or energy modeler runs
simulations
! Loads vs. systems energy
! Modeling building energy consumption at early stages of
design, when detailed inputs are not known
! Trade-off between accuracy and complexity

5. “Building Energy Loads Analysis” (BELA)
! Simple, easy to use, flexible program
! Evaluate high-level design options as well as detailed
design of new and innovative systems
! Transparent, demonstrate the application of first
principles to estimate annual energy consumption

6. Program Structure

7. Inputs
Inputs Loads Systems

8. Weather
! Canadian Weather for Energy Calculations (CWEC)
! Hourly weather data for a “typical” year
! Temperature, relative humidity, solar radiation, wind
Inputs Loads Systems

9. Schedules
! Lighting
! Plug loads
! Occupancy
! Daily and Weekly
Inputs Loads Systems

10. Calculation of Loads
! Conduction
! Walls, Roof, Foundation, Windows, Doors
! Solar heat gain (windows)
! Infiltration
! Internal Gains: People, Lights, Plug Loads
! Ventilation
Inputs Loads Systems

11. Thermal Mass
! Transfer function method used in current version
! Apply weighting factor to instantaneous gain or loss
! Better methods available and could be implemented for
future versions (eg. Radiant Time Series)
= Heating or cooling load at hour θ
= Heating or cooling load at hour θ – 1
= Instantaneous heat gains or losses at hour θ
= Instantaneous heat gains or losses at hour θ – 1
V0, V1, W1 = Weighting factors
Inputs Loads Systems

12. Display Heating and Cooling Loads
! Determine significant loads
! Where to focus efforts for energy upgrades
August Cooling Loads
Inputs Loads Systems
January Heating Loads
Conduction
44%
Infiltration
50%
Ventilation
6%
Conduction
1% Infiltration
4%
Window Solar
Heat Gain
30%
Occupants
17%
Plug Loads
28%
Lights
19%
Ventilation
1%

13. Display Heating and Cooling Loads
Inputs Loads Systems
15
10
5
0
-5
-10
-15
-20
-25
-30
Monthly Load Density, kWh/m2
Ventilation
Window SHG
Infiltration
Conduction
Occupants
Plug Loads
Lights
Monthly Load Intensity, kWh/m2

14. Display Heating and Cooling Loads
! Determine energy impact of design options
Inputs Loads Systems
180000
160000
140000
120000
100000
80000
60000
40000
20000
0
R5 Wall R20 Wall R40 Wall R60 Wall
Load, kWh
January Heating Loads
Wall Insulation Comparison
Ventilation
Infiltration
Conduction

15. Calculation of Systems Energy
! BELA currently assumes radiant heating and cooling with
Dedicated Outdoor Air System (DOAS) ventilation
Radiant with DOAS Energy Intensity, kWh/m2
Inputs Loads Systems
30
25
20
15
10
5
0
Energy Density {kWh/m2}
Radiant with DOAS Energy Density
Ventilation Distribution
Ventilation Cooling
Ventilation Heating
Space Distribution
Space Cooling
Space Heating
Plug Loads
Lights

16. Case Study
! Compare results of BELA to eQuest for a small office
building
! Reason for this analysis
! To view the differences between results from a simple model
built upon fundamental principles to a more developed but
less transparent program
! Goal is not to “calibrate” the two models to give the same
output
! Similar to a project early in the design stages where
detailed inputs are not known
! Programs use similar calculation methods

17. Case Study: Small Office Building
! Typical small office building adapted from B.M. Ross 2009
! Four enclosure assemblies with different levels of thermal
performance,
! Exemplary
! High performance
! Institutional
! Market

18. Case Study Comparison
Exemplary High
Performance
Institutional Market
BELA eQuest BELA eQuest BELA eQuest BELA eQuest
Pump Power 2.1 8.8 2.7 13.3 3.0 11.8 4.1 17.2
Space Heating 72.5 68.7 139.6 164.2 283.0 227.6 452.9 464.7
Space Cooling 29.4 27.4 32.6 26.7 22.9 22.7 23.8 26.8
Fan Power 3.0 8.3 3.0 8.3 3.0 8.3 3.0 8.3
Lights 38.4 41.5 38.4 41.5 38.4 41.5 38.4 41.5
Plug Loads 43.8 47.9 43.8 47.9 43.8 47.9 43.8 47.9
Total 189.3 202.3 260.1 301.9 394.2 359.9 566.0 606.4
Difference -6% -14% 10% -7%

19. Case Study Comparison
Exemplary High
Performance
Institutional Market
BELA eQuest BELA eQuest BELA eQuest BELA eQuest
Pump Power 2.1 8.8 2.7 13.3 3.0 11.8 4.1 17.2
Space Heating 72.5 68.7 139.6 164.2 283.0 227.6 452.9 464.7
Space Cooling 29.4 27.4 32.6 26.7 22.9 22.7 23.8 26.8
Fan Power 3.0 8.3 3.0 8.3 3.0 8.3 3.0 8.3
Lights 38.4 41.5 38.4 41.5 38.4 41.5 38.4 41.5
Plug Loads 43.8 47.9 43.8 47.9 43.8 47.9 43.8 47.9
Total 189.3 202.3 260.1 301.9 394.2 359.9 566.0 606.4
Difference -6% -14% 10% -7%
Reason for difference?

20. Case Study Comparison
Exemplary High
Performance
Institutional Market
BELA eQuest BELA eQuest BELA eQuest BELA eQuest
Pump Power 2.1 8.8 2.7 13.3 3.0 11.8 4.1 17.2
6% -15% 24% -3%
Space Heating 72.5 68.7 139.6 164.2 283.0 227.6 452.9 464.7
Space Cooling 29.4 27.4 32.6 26.7 22.9 22.7 23.8 26.8
Fan Power 3.0 8.3 3.0 8.3 3.0 8.3 3.0 8.3
Lights 38.4 41.5 38.4 41.5 38.4 41.5 38.4 41.5
Plug Loads 43.8 47.9 43.8 47.9 43.8 47.9 43.8 47.9
Total 189.3 202.3 260.1 301.9 394.2 359.9 566.0 606.4
Difference -6% -14% 10% -7%

21. Case Study Comparison
Exemplary High
Performance
Institutional Market
BELA eQuest BELA eQuest BELA eQuest BELA eQuest
Pump Power 2.1 8.8 2.7 13.3 3.0 11.8 4.1 17.2
Space Heating 72.5 68.7 139.6 164.2 283.0 227.6 452.9 464.7
7% 22% 1% -11%
Space Cooling 29.4 27.4 32.6 26.7 22.9 22.7 23.8 26.8
Fan Power 3.0 8.3 3.0 8.3 3.0 8.3 3.0 8.3
Lights 38.4 41.5 38.4 41.5 38.4 41.5 38.4 41.5
Plug Loads 43.8 47.9 43.8 47.9 43.8 47.9 43.8 47.9
Total 189.3 202.3 260.1 301.9 394.2 359.9 566.0 606.4
Difference -6% -14% 10% -7%

22. In Summary
! Simple energy modeling program developed using
fundamental principles
! Transparent, adaptable, suitable for high level design
! Limitations
! Single zone
! Many areas for improvement in accuracy and range of
capabilities

23. Questions?