1. Lecture 5: Building Envelope Description (Part I)
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Material prepared by GARD Analytics, Inc. and University of Illinois
at Urbana-Champaign under contract to the National Renewable Energy
Laboratory. All material Copyright U.S.D.O.E. - All rights reserved

2. Importance of this Lecture to the Simulation of Buildings
Every building is different in many ways:
Location/exterior environment
Construction/building envelope
HVAC system
Building envelope/construction determines how a building will respond to the exterior environment
Thermal simulation requires information about the physical make-up of the building, where various constructions are located and how they are oriented, how the building is subdivided into zones, etc.
Thermal simulation requires information on the building envelope to properly analyze the building from an energy perspective

3. Purpose of this Lecture
Gain an understanding of how to specify the building construction
Groups of Surfaces (Zones) and Overall Building Characteristics
Walls, Roofs, Ceilings, Floors, Partitions, etc.
Materials and Groups of Materials (Constructions)

4. Keywords Covered in this and next Lecture
Building
Zone
SurfaceGeometry
Surface (all types)
Construction
Material:Regular
Material:Regular-R
Material:Air

5. Definitions and Connections
Building:
Entire collection of interior and exterior features of the structure
Buildings may consist of one or more zones
Zones:
Group of surfaces that can interact with each other thermally and have a common air mass at roughly the same temperature
One or more rooms within a building
Zones may consist of one or more surfaces

6. Definitions and Connections (cont’d)
Surfaces:
Walls, Roofs, Ceilings, Floors, Partitions, Windows, Shading Devices
One or more surfaces make up a zone
Surfaces consist of a series of materials called a “construction”
Construction:
Group of homogeneous one-dimensional material layers
Each surface must have a single construction definition
Each construction is made up of one or more materials

7. Definitions and Connections (continued)
Materials:
Define the thermal properties for layers that are used to put together a construction
One or more material layers make a construction

8. Envelope Hierarchy Building Zone Zone Zone … more zones
… more surfaces
Surface
Surface
Surface
Surface
only one construction per surface
Construction
… more materials
Material
Material
Material
Material

9. More on Zones
Thermal zone definition very generic and does not answer the following questions:
How many surfaces to a zone?
How many zones should be defined for a particular building?
Should each room be a zone?
Can the entire building be a zone?

10. Defining Thermal Zones by Objective
Objectives of a study can dictate the size and number of thermal zones
Air flow study: sizing fans and ducts
Several rooms per zone
Zone per system type
“Block loads” or central plant study: sizing of heating and cooling producers
Minimize number of zones (maybe only 1)

11. Ft. Monmouth Education Center

12. Defining Thermal Zones by Design Conditions
“DT” test: if there is an air temperature difference between adjacent spaces, separate thermal zones are needed
Might also be seen in different control types

13. Defining Thermal Zones by Design Conditions (cont’d)
Space usage/internal gains test:
Differences in internal gains may result in different conditioning requirements or distribution
Office vs. gymnasium
Space usage differences may alter the ventilation or exhaust requirements of a space
Office vs. kitchen vs. chemistry laboratory

14. Defining Thermal Zones by Design Conditions (cont’d)
Environmental conditions test: exposure to different thermal surroundings/quantifying the effect
Different space orientations—solar gains
Exposure to the ground
Exposure to the outdoor environment

15. Ft. Monmouth Education Center
“DT” test: loading dock
Space use: kitchen, dining area
Outdoor exposure: west wing solar

16. Loads Features and Capabilities
How does EnergyPlus calculate what it will take to keep a zone at the desired thermal conditions?
EnergyPlus contains the heat balance engine from IBLAST, a research version of BLAST with integrated loads and HVAC calculation.
The major enhancements of the IBLAST heat balance engine include mass transfer and radiant heating and cooling
Essentially identical in functionality to the Loads Toolkit developed under ASHRAE Research Project (RP-987)
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17. Loads Features and Capabilities (cont’d)
Heat balance engine models room air as well-stirred with uniform temperature throughout.
Room surfaces are assumed to have:
Uniform surface temperatures
Uniform long and short wave irradiation
Diffuse radiating and reflecting surfaces
Internal heat conduction
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18. EnergyPlus Model For Building Loads
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19. Equipment & People Loads
Sensible and Latent
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20. Loads Features and Capabilities (cont’d)
Three models connected to the main heat balance routine are based on capabilities from DOE­2
Daylighting simulation
Calculates hourly interior daylight illuminance, window glare, glare control, electric lighting controls, and calculates electric lighting reduction for the heat balance module
WINDOW 5-based window calculation
Anisotropic sky
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21. Loads Features and Capabilities (cont’d)
Several other modules have been reengineered for inclusion in EnergyPlus:
Solar shading from BLAST
Conduction transfer function calculations from IBLAST
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22. Loads Features and Capabilities (cont’d)
Incorporates a simplified moisture model known as Effective Moisture Penetration Depth (EMPD)
Estimates moisture interactions among the space air and interior surfaces and furnishings
Estimates impacts associated with moisture where detailed internal geometry and/or detailed material properties are not readily available
User may also select a more rigorous combined heat and mass transfer model
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23. Loads Features and Capabilities (cont’d)
Loads and systems portions more tightly coupled than in BLAST or DOE-2.
Loads calculated on a time step basis and passed directly to the HVAC portion.
Loads not met result in zone temperature and humidity changes for the next time step.
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24. Keyword: Building IDD Description (shortened)
Purpose: to control basic information about the building location, its orientation, its surroundings, and some simulation parameters
BUILDING,
A1 , \field Building Name
N1 , \field North Axis
A2 , \field Terrain
N3 , \field Loads Convergence Tolerance Value
N4 , \field Temperature Convergence Tolerance Value
A3 ; \field Solar Distribution

25. North Axis Interpretation:
Keyword: Building
IDD Description (detailed)
Keyword
BUILDING,
\unique-object
\required-object
\min-fields 6
A1 , \field Building Name
\required-field
\default NONE
N1 , \field North Axis
\note degrees from true North
\units deg
\type real
\default 0.0
User defined building name
Allows rotation of the entire building for the convenience of the user
True North
Building North
North Axis Interpretation:
Angle is North Axis (+45 in this case)

26. Keyword: Building IDD Description (detailed, continued)
Allows specification of immediate surroundings of the building
A2 , \field Terrain
\note Country=FlatOpenCountry
\note Suburbs=RoughWoodedCountryTownsSuburbs
\note City=CityCenter
\type choice
\key Country
\key Suburbs
\key City
\default Suburbs
N3 , \field Loads Convergence Tolerance Value
\units W
\type real
\minimum> 0.0
\default .04
Note: Terrain mainly affects exterior convection correlations
Options and their approximate descriptions
Advanced user feature that should be left as the default in most cases

27. Keyword: Building IDD Description (detailed, continued)
N4 , \field Temperature Convergence Tolerance Value
\units deltaC
\type real
\minimum> 0.0
\default .4
A3 ; \field Solar Distribution
\note MinimalShadowing | FullExterior
\note FullInteriorAndExterior
\type choice
\key MinimalShadowing
\key FullExterior
\key FullInteriorAndExterior
\default FullExterior
Advanced user feature that should be left as the default in most cases
See next two slides for descriptions

28. Solar Distribution Options
Minimal Shadowing
No exterior shadowing except from door and window reveals
All direct beam solar radiation incident on floor
If no floor, direct beam solar distributed to all surfaces
Full Exterior
Exterior shadowing caused by detached shading, wings, overhangs, and door and window reveals

29. Solar Distribution Options (cont’d)
Full Interior and Exterior
Exterior shadowing same as Full Exterior
Direct beam solar radiation falls on all surfaces in the zone in the direct path of the sun’s rays
Solar entering one window can leave through another window
Zone must be convex:
A line passing through the zone intercepts no more than two surfaces
An L-shaped zone is not convex

30. Convex Zones

31. Keyword Example: Building
IDF Example or
BUILDING, NONE, 0.0, Suburbs, 0.4, 0.4, FullExterior;
BUILDING,
NONE, !- Building Name
0.0, !- North Axis {deg}
Suburbs, !- Terrain
0.4, !- Loads Convergence Tolerance Value {W}
0.4, !- Temperature Convergence Tolerance Value {C}
FullExterior; !- Solar Distribution

32. Summary
EnergyPlus input files contain a hierarchy of envelope input that includes the Building, Zone, Surface, and Construction definitions
Simulation of the building envelope based on a heat balance applied to a thermal zone
Buildings consist of one or more thermal zones—number of zones based on various factors including space usage, environmental conditions, etc.
EnergyPlus provides access to more detailed simulation of daylighting, windows, moisture, etc.