How do minor orientation changes impact the building EUI?

June 28, 2019 - 7 minutes read

Short Answer: It depends significantly on your glazing percentage. If you have a glazing percentage of 60% of less, and you are making orientation changes of less than 45°, on average, it leads to an impact of less than 1.2 Kbtu/sf/yr. In the broad picture, that impact is quite minimal with the uncertainty at play for early stage energy modeling. Of course, these are the “cliff note” version of the study, read the full study below.

  1. Introduction:

Building
Energy Modeling (BEM) is a physics-based computer simulation of a building that
can be used to analyze and predict the energy consumption, HVAC component
sizing and utility bills. BEM is used in new building construction and retrofit
designs to achieve compliance for the energy code standards (ASHRAE 90.1, Title
24, NECB), different green building certifications like LEED v4 & Green
Globes. BEM input parameters that are taken into consideration for running the
simulation include but not limited to building geometry, construction material
properties, glazing ratio, lighting, HVAC system, refrigeration, service water
heating, component efficiencies, control strategies and renewable generation
system configurations.

                The purpose of this study is to
observe the sensitivity of building rotation on Energy Use Intensity (EUI). All
simulation parameters are kept constant except the site orientation to record
the impact on energy consumption. The study is conducted using the small office
building prototype provided by Pacific National Northwest Laboratory (PNNL).

  • Key
    Observations:

The Energy Usage Intensity (EUI) is observed for single zone small office PNNL prototype model for 10°, 20°, 30° and 45° rotated clockwise as well as anticlockwise. The EUI difference for Miami, Florida (ASHRAE Climate Zone 1A), Atlanta, Georgia (ASHRAE Climate Zone 3C) and Denver, Colorado (ASHRAE Climate Zone 5B) was observed to be 0.63 kBtu/ft2, 0.72 kBtu/ft2 and 0.92 kBtu/ft2 respectively for the rotation range described earlier.    

Furthermore, the next iteration was done by adding 20% more glazing on all sides and rotating the single zone small office PNNL prototype model by 10°, 20°, 30° and 45° clockwise and anticlockwise. After running the simulations, the EUI difference for Miami, Florida (ASHRAE Climate Zone 1A), Atlanta, Georgia (ASHRAE Climate Zone 3C) and Denver, Colorado (ASHRAE Climate Zone 5B) was observed to be 1.05 kBtu/ft2, 1.10 kBtu/ft2 and 1.33 kBtu/ft2 respectively for the considered rotation range.  

  • Methodology:
  • Building
    Parameters:

The selected building is a small office prototype described
by Pacific Northwest National Laboratory (PNNL). Some of the building
parameters are mentioned below:

Total Area of the Building (Sqft) 5055
Number of Floors 1
Window Fraction 24.4% for South, 19.8% for other three
orientations
Thermal Zoning Single Zone Model
Floor to Floor Height (Ft) 10
HVAC System Type Air-source heat pump with gas furnace as back up
Thermostat Setpoint 75°F Cooling/70°F Heating
Thermostat Setback 85°F Cooling/60°F Heating
Lighting Power Density (LPD) (W/Sqft) 0.98
Equipment Power Density (W/Sqft) 1.0935
Domestic Hot Water Consumption Rate (gal/ft2-day) 0.004908
Heating System COP 1.8
Cooling System COP 1.8
  1. Rotation
    Range and Glazing Variation:

The single thermal zone is considered for running the simulations. The PNNL small office model is created utilizing DesignBuilder (EnergyPlus) and rotated along North-South axis by 10°, 20°, 30° and 45° in clockwise and anticlockwise sense as shown in following figure. The next step involved adding 20% more glazing on all sides of the prepared model and rerunning the simulation.

Figure 1 Rotation Range for Single
Zone PNNL Small Office Prototype along North-South Axis

  • Comparison
    of Energy Usage Intensity:

The following cities are used to
study the impact of rotating the single zone PNNL small office prototype:

ASHRAE Climate Zone City
1A Miami,
Florida
3C Atlanta, Georgia
5B Denver,
Colorado
  1. Zone 1A Miami, Florida:

Figure 2 Miami PNNL Small Office Rotation Comparison for Different Angles

Figure 3 Miami PNNL Small Office with 20% more Glazing Rotation Comparison for Different Angles

The
highest EUI difference of 0.63 kBtu/ft2 is recorded by rotating the model by 45° anticlockwise along N-S axis. When
the glazing is increased by 20%, the highest EUI difference became 1.05
kBtu/ft2 for 45°
anticlockwise rotation along N-S axis.

  • Zone 3A Atlanta, Georgia:

Figure 4 Atlanta PNNL Small Office Rotation Comparison for Different Angles

Figure 5 Atlanta PNNL Small Office with 20% more Glazing Rotation Comparison for Different Angles

The highest
EUI difference of 0.72 kBtu/ft2 is recorded by rotating the model by 45° anticlockwise along N-S axis. When
the glazing is increased by 20%, the highest EUI difference became 1.1 kBtu/ft2
for 45°
anticlockwise rotation along N-S axis.

  • Zone 5B Denver, Colorado:

Figure 6 Denver PNNL Small Office Rotation Comparison for Different Angles

Figure 7 Denver PNNL Small Office with 20% more Glazing Rotation Comparison for Different Angles

The
highest EUI difference of 0.92 kBtu/ft2 is recorded by rotating the model by 45° anticlockwise along N-S axis. When
the glazing is increased by 20%, the highest EUI difference became 1.33
kBtu/ft2 for 45°
anticlockwise rotation along N-S axis.

  • Conclusion:

The time
invested in adjusting the building orientation and thermal zone manipulation for
every design change can be eliminated with the proposed method described in the
study. Moreover, the project team will be able to perform more simulations to
test out different design options to choose the best design without worrying
about specific building orientation. The facts presented will surely help to
optimize the conceptual design phase and thereby saving huge amount of money
and time of the owner and the project team.

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