Alternative Runs (Details)

Detail information on Alternative Runs for Potential Energy Savings Chart.

The alternative runs that drive the Potential Energy Savings chart are currently defined by Autodesk and are chosen to provide a range of results that gives a good overall picture of how sensitive energy performance is to a range of different building features.

The parameters tested span a range of possibilities that you would find in very efficient buildings, as well as very inefficient buildings. For example, very efficient lighting can be installed in any building type or climate, and you will find very inefficient systems and envelopes in existing buildings. To show how energy sensitive your building design is to these possibilities we simulate results that represent this broad span of possibilities.

The alternative runs for plug loads, lighting efficiency, and infiltration depend on three characteristics of your model: Building Type, Building Size, and Location. For all of the other building features, the same alternative runs are applied for all building types, sizes, and locations.

Parameter Values Simulated for Potential Energy Savings chart

The information below will help you understand exactly what’s behind the analysis, so you can make the most informed decisions.

Building Geometry

Building Orientation

Values simulated: The building model is rotated from the base run’s orientation in 45° increments to cover all eight 45° quadrants (the base run and 7 alternatives).

To rotate the building, the project north parameter is rotated either clockwise or counterclockwise. Negative values denote a counter-clockwise rotation and positives values denote a clockwise rotation.

Why these values were chosen: Forty-five degree rotation is the smallest increment that is likely to have a notable effect on building performance, so the 45° increments are sufficient for studying a project’s sensitivity to orientation. The impact of orientation will depend upon your building’s geometry, location, window sizes and positions, and glass characteristics.

that Appendix G of ASHRAE 90.1-2007, which is referenced by LEED standards, requires that a baseline energy simulation be independent of the building’s orientation. This is done by averaging the results of a simulation of the building with its actual orientation and simulations after rotating the entire building 90, 180, and 270 degrees, then averaging the results. You can get this baseline value by averaging the output of the original run and the three appropriate alternative runs. For more information on Orientation, see the Autodesk Sustainability Workshop.

Links and references: ASHRAE 90.1-2007 – Appendix G

Building Construction

Wall construction

Values Simulated: Wall construction alternatives simulated are the same for all climates. Two alternative runs are simulated.

       

English

Metric

R-value

(h*F*ft2)/ BTU

U-value

BTU/ (h*F*ft2)

R-value

(m²-K)/ W

U-value

W / (m²-K)

Uninsulated_framed_ Wall

Metal Frame Wall without Insulation

1.72

0.58

0.31

3.26

R-44_framed_Wall

Structurally Insulated Panel (SIP) Wall 12.25 inches (311 mm) thick, 48 inch on-center R-44 insulation

37.3

0.03

6.43

0.15

Why these values were chosen: The wall construction parameters represent extremes in thermal resistance values in new and existing buildings. Note that the metal frame wall without insulation has extremely poor insulating properties (very high conductivity). Be aware of this when analyzing this bar on the Potential Energy Savings Chart.

Roof Construction

Values Simulated: Roof construction alternatives simulated are the same for all climates. Two alternatives are simulated:

       

English

Metric

R-value

(h*F*ft2)/ BTU

U-value

BTU/ (h*F*ft2)

R-value

(m²-K)/ W

U-value

W / (m²-K)

Uninsulated_framed_ Roof

Metal Frame Roof without Insulation

2.1

0.48

0.37

2.72

R-60_continuous_Ins_ Roof

Wood Frame Roof with R-60 insulation

66.2

0.02

12.5

0.08

Why these values were chosen: The roof construction parameters represent extremes in thermal resistance values in new and existing buildings. Note that the metal frame roof without insulation has extremely poor insulating properties (high conductivity). Be aware of this when analyzing this bar on the Potential Energy Savings Chart.

Window Glass

Values Simulated: Window glass alternatives simulated are the same for all climates. Four alternative runs are simulated:

   

English U-value

BTU/ (h*F*ft2)

Metric U-value

W / (m²-K)

SHGC

 

Visible Light Transmission (VLT)

Quad_Kryp_Clear_Skylight

Low U-value

Moderate SHGC

High VLT

0.12

0.68

0.45

0.62

Dbl_LowE_HP_Skylight

Low U-value

Low SHGC

High VLT

0.29

1.65

0.27

0.64

Triple_LowE_film_Skylight

Low U-value

Low SHGC

Low VLT

0.31

1.76

0.2

0.22

Single_Low_Iron_Skylight

High U-value

High SHGC

High VLT

1.11

6.30

0.9

0.91

Why these values were chosen: The three main characteristics of glass (U-value, SHGC, and VLT) each impact energy usage in a different way, a characteristic that is beneficial in one climate may not be in another. The glass parameters were chosen to isolate the effects of each characteristic by holding the value of one somewhat constant while varying another. This will provide a better idea of how sensitive your building is to glazing choices in a variety of climates and uses.

Buildings in cooling-dominated climates tend to be more sensitive to SHGC (a measure of radiant heat transfer), while buildings in heating-dominated climates tend to be more sensitive to U-values (heat flow). The VLT is a measure of visible light that can pass through the glass and will affect energy use in a building with daylight dimming by increasing or reducing the available daylight. For more information on Glazing Properties, see the Autodesk Sustainability Workshop.

Skylight Glass

Values Simulated: Skylight glass alternatives simulated are the same for all climates. Skylight glass alternatives are the same as the window glass alternatives. 4 alternative runs are simulated:

   

English U-value

BTU/ (h*F*ft2)

Metric U-value

W / (m²-K)

SHGC

 

Visible Light Transmission (VLT)

Quad_Kryp_Clear_Skylight

Low U-value

Moderate SHGC

High VLT

0.12

0.68

0.45

0.62

Dbl_LowE_HP_Skylight

Low U-value

Low SHGC

High VLT

0.29

1.65

0.27

0.64

Triple_LowE_film_Skylight

Low U-value

Low SHGC

Low VLT

0.31

1.76

0.2

0.22

Single_Low_Iron_Skylight

High U-value

High SHGC

High VLT

1.11

6.30

0.9

0.91

Why these values were chosen: Consistency between skylight and window glass alternatives.

Infiltration

Values Simulated: High or Low volume of unconditioned outdoor air leaking into conditioned spaces.

Why these values were chosen: The infiltration values represent the extreme range seen in new and existing buildings. Note that 3.5 ACH is a very high infiltration rate. Be aware of this when analyzing this bar on the Potential Energy Savings Chart.  
Note: There is little experimental research or measurements done on building infiltration, and actual infiltration is very hard to be estimated for an unbuilt or existing building, so we feel the ranges we present here represent the best estimate for what could occur in buildings.

Equipment and Lighting  

Lighting Efficiency  

Values Simulated: The lighting power density (Watts/ft2 or Watts/m2) of your project is set by defaults that are based on the building type you’ve specified. See GBS default values by building type.

Why these values were chosen: The low efficiency value is taken from the ASHRAE 90.1-2001 Standard to represent existing construction. The high efficiency lighting values are based upon a case study design calculations which represents a 63% reduction in baseline lighting power density below ASHRAE 90.1 2001 (56% below ASHRAE 90.1 2004) (see reference below). The 63% reduction is applied to all building types, assuming the same level of efficiency is feasible.

Links and references: “Double Performance LEED Performance: National Grid Optimal Lighting/Minimal Energy” Terry Clark, Founder and CEO Finelite, Inc., page 42.

Plug Load Efficiency

Values Simulated: The electric power density, or plug loads, (Watts/ft2 or Watts/m2) of your project is set by defaults that are based on the building type you’ve specified. See GBS default values by building type.

Note that electric power density is not affected by any space types you’ve defined, base plug loads are set globally by building type.

Why these values were chosen: Plug load baseline levels are not mandated by ASHRAE 90.1. GBS uses the plug load levels stipulated by the California Energy Code (Title 24) 2005 as a reasonable default baseline.

Links and references: California Energy Commission 2005 Building Energy Efficiency Standards; Nonresidential Alternative Calculation Method (ACM) Manual, Table N2-2.

Lighting Controls

Daylighting Controls

Daylighting controls can automatically control electric lighting levels based on daylight availability.

When set to ON, the baseline lighting power density is adjusted to account for the savings associated with automatic daylight controls. The lighting power adjustment uses the California Energy Commission’s method of applying daylighting control factors.

Green Building Studio also automatically places DOE2 daylight sensors within each daylit space of the building. When these sensors measure a light level from daylight above 30 footcandles (322 lux), the lights in the space are turned off. Because sensor placement is very sensitive to model quality, these sensors are disabled in the simulation, and the alternative CEC method of lighting power adjustment is used. For advanced modeling workflows in eQuest, these sensors can be reactivated.

Values simulated:  In the baseline model, daylighting controls are off. To test the effect of Daylighting Controls, one alternative run is simulated with daylighting controls ON.

Note that the alternative run named ‘BaseRun_w/DC_ON’ is the alternative with daylighting controls ON and with the window glass characteristics of the submitted model.

Also, because daylight availability is determined by glazing properties and aperture placement, daylighting controls (DC) are tested with alternative window and skylight glazing. The same four glazing alternatives cited for those parameters are used for both skylight and window glass with daylighting controls applied for 8 additional simulations:

  1. Quad_Kryp_Clear_w/DC

  2. Dbl_LowE_HP_Window_w/DC

  3. Triple_LowE_film_Window_w/DC

  4. Single_Low_Iron_Window_w/DC

  5. Quad_Kryp_Clear_Skylight_w/DC

  6. Dbl_LowE_HP_Skylight_w/DC

  7. Triple_LowE_film_Skylight_w/DC

  8. Single_Low_Iron_Skylight_w/DC

Why these values were chosen: For most non-residential buildings, lighting can be one of the largest electric energy end-uses. Implementing designs that can decrease the lighting energy is one of the most effective ways to improve your building’s energy efficiency. GBS calculates daylighting energy savings using the California Energy Commission method of applying an adjustment to the lighting power density, rather than simulating the daylighting in DOE-2. A separate calculation is done for each space in the model. These calculations factor in the room geometry, window/skylight placement and geometry, and the visible lighting transmittance (VLT) of the glazing. The California Energy Commission method is a more conservative approach than the DOE-2 simulation method. For more information on Lighting and Daylighting, see the Autodesk Sustainability Workshop.

Links and References: California Energy Commission 2008 Building Energy Efficiency Standards for Residential and Non-Residential Buildings, Section 146 Prescriptive Requirements for Indoor Lighting.

Occupancy Sensors

Occupancy sensors are On/Off controls for lighting systems according to occupancy. When set to 'On', lighting is turned off automatically when no occupants are in the space. The effect of this will be to reduce lighting energy use which will also reduce cooling energy use accounted for in the simulation.

Values Simulated: In the baseline model, occupancy controls are off. To test the effect of Occupancy Controls, one alternative run is simulated.

Why these values were chosen: The lighting power density is reduced for the Occupancy Sensor parameter. The reduction is based upon the power adjustment used by ASHRAE 90.1. Spaces less than 5000 square feet are credited with a 15% reduction in lighting power density; spaces greater than 5,000 square feet are credited with a 10% reduction (see the reference below).

Links and References: ASHRAE Standard 90.1, Table G3.2 Power Adjustment Percentages for Automatic Lighting Controls

Parent topic: Potential Energy Savings (PES) Chart