Transcript Lecture 05 Building Envelope

Lecture 5: Building Envelope
Description (Part I)
Material prepared by GARD Analytics, Inc. and University of Illinois
at Urbana-Champaign under contract to the National Renewable Energy
Laboratory. All material Copyright 2002-2003 U.S.D.O.E. - All rights reserved
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
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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)
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Keywords Covered in this and
next Lecture
Building
Zone
SurfaceGeometry
Surface (all types)
Construction
Material:Regular
Material:Regular-R
Material:Air
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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
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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
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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
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Envelope Hierarchy
Building
Surface
Zone
Zone
Zone
Surface
Surface
Surface
Material
… more surfaces
only one construction per surface
Construction
Material
… more zones
Material
Material
… more materials
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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?
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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)
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Ft. Monmouth Education
Center
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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
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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
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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
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Ft. Monmouth Education
Center
 “DT” test:
loading dock
 Space use:
kitchen, dining
area
 Outdoor
exposure:
west wing
solar
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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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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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EnergyPlus Model For
Building Loads
Conditioned Air
Internal
Radiation
Heat Transfer
(Diffusion and Storage)
Solar Beam
Tair
Return Air
Diffuse Solar
Reflected Solar
Internal
Radiation
Heat &
Moisture
Source (P eople
& Equipment)
Convection
Infiltration
(Sensible & Latent)
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Equipment & People Loads
Sensible and Latent
Convection
Radiation
Equipment
Occupant
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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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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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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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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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Keyword: Building
IDD Description (shortened)
BUILDING,
A1 , \field
N1 , \field
A2 , \field
N3 , \field
N4 , \field
A3 ; \field
Building Name
North Axis
Terrain
Loads Convergence Tolerance Value
Temperature Convergence Tolerance Value
Solar Distribution
Purpose: to control basic information
about the building location, its
orientation, its surroundings, and some
simulation parameters
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Keyword: Building
IDD Description (detailed)
Keyword
BUILDING,
\unique-object
\required-object
\min-fields 6
User defined building name
A1 , \field Building Name
\required-field
\default NONE
N1 , \field North Axis
Allows rotation of the entire
\note degrees from true North building for the convenience
\units deg
of the user
\type real
True North
\default 0.0
Building North
North Axis Interpretation:
Angle is North Axis
(+45 in this case)
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Keyword: Building
IDD Description (detailed, continued)
Allows specification of
immediate surroundings
A2 , \field Terrain
\note Country=FlatOpenCountry of the building
\note Suburbs=RoughWoodedCountryTownsSuburbs
\note City=CityCenter
Note: Terrain
\type choice
mainly affects
\key Country
Options and their
exterior
\key Suburbs
approximate descriptions convection
\key City
correlations
\default Suburbs
N3 , \field Loads Convergence Tolerance Value
\units W
Advanced user feature that
\type real
should be left as the default
\minimum> 0.0
in most cases
\default .04
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Keyword: Building
IDD Description (detailed, continued)
N4 , \field Temperature Convergence Tolerance Value
\units deltaC
Advanced user feature that
\type real
should be left as the default
\minimum> 0.0
in most cases
\default .4
A3 ; \field Solar Distribution
\note MinimalShadowing | FullExterior
\note FullInteriorAndExterior
\type choice
\key MinimalShadowing
See next two
\key FullExterior
slides for
\key FullInteriorAndExterior
descriptions
\default FullExterior
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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
 All direct beam solar radiation incident on floor
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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
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Convex Zones
Convex zones
Non-Convex zones
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Keyword Example: Building
IDF Example
BUILDING, NONE, 0.0, Suburbs, 0.4, 0.4, FullExterior;
or
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
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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.
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