Transcript EnergyPlus Training Part 1

Lecture 12: Building
Technology and Strategies for
Sustainability
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
 Energy consumption of buildings (heating,
cooling, and lights) is a significant fraction of
energy consumption worldwide
 Many energy sources are finite so we must
slow down energy consumption as much as
possible
 Simulation can help reduce energy
consumption by modeling various strategies
before they are built thus minimizing energy
costs
 Knowledge of various techniques for
“sustainable design” and what can be
simulated is crucial
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Purpose of this Lecture
Gain an understanding of:
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Some basic strategies for reducing the
energy cost of buildings
Various technology solutions that are
currently available
A few “green” capabilities of EnergyPlus
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General Strategies for Reducing
Building Heating and Cooling
 Non-mechanical system approach
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Should always try to minimize heating and cooling
requirements first
Mechanical system efficiency important also
 Building Envelope: Insulation and/or Isolation
 Solar Strategies (Passive Heating)
 Alternate Cooling Strategies
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Building Envelope: Insulation
and/or Isolation
 Goal: Attempt to minimize the adverse effects
of the environment on a building
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Note: effect of environment is always changing
Note: in some cases (e.g., temperate/mild climates
and high internally loaded buildings), we may
want to maximize impact of environment because
it is beneficial (Climate Specific Strategies)
 Adjust volume to exterior area ratio
 Volume/living space desirable (maximize volume)
 Minimizing exterior surface area (usually) since it
affects conduction, convection, and radiation
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Building Envelope: Change Wall
Construction
 Reduce conduction by adding insulation
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Conduction (q=ADT/R)increase in R decreases q
Note differences in R-values of various exterior surfaces
and their relative areas
 Windows vs. walls: windows generally have a lower R-value
 Walls vs. roofs: building shape determines where to focus
attention
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Consider the possibility of movable insulation for various
surfaces
 Potentially reduce conduction by adding thermal mass
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“Interior” internal mass damps various short term effects,
reducing or shifting conditioning needs
“Exterior thermal mass delays impact of exterior
temperature swings, may send some/much of effect back
to exterior side
Thermal mass discussed in more detail later in this lecture
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Building Envelope: Change
Exterior Boundary Conditions
 Create a local “micro-climate”
 Air vs. ground temperature
 Ground can be a thermal mass and insulator
 Air temperature changes more extreme (harm or
help?)
 Modification of air temperature using site water
resources (evaporative cooling to reduce local air
temperature)
 Wind exposure
 Use of vegetation as wind breaks in winter
(evergreens on north side—location specific)
 Allow air movement for cooling?
 Note surroundings and impact on air movement
around building
 Surface properties
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Solar Radiation: Light and Heat
 General concepts
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Use solar energy when heating required, avoid it
when cooling is required
Sun angles (particularly altitude) can vary with
time of yearthis can work to our advantage
Solar adds heat and light, but only during the day
Orientation of openings (windows) critical to the
success of the design; in general:
 Maximize southern exposure
 Minimize east/west exposure
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Solar Radiation: Light and Heat
(cont’d)
“Passive solar” increasingly important in
design
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A definition: “a system that collects,
stores, and redistributes solar energy
without the use of fans, pumps, or
complex controllers” (Lechner)
Lower first costs than active solar
systems because they are part of the
building rather than an additional
syste
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Solar Radiation: Light and Heat
(cont’d)
 Using Direct Solar Gain (Windows)
 Utilize the “greenhouse effect” of windows which allow solar
radiation to be transmitted but block most thermal radiation
 Benefit is maximized with south facing windows
 Low winter sun more directly impacts this direction
 High summer sun has little effect on south windows,
can be easily shaded
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Potential for overheating during the day and underheating at
night
 Thermal mass (interior) helps reduce this effect
 Need to exercise caution about thermal mass color and
location relative to insulators such as carpet, furniture,
etc.
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Direct gain easy to provide but there are limitsincreasing
windows to increase gain also increases heat loss through
windows (at night) or heat gain when undesirable (in
summer)
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Solar Radiation: Systems
 Trombe Wall Systems (more details later in
this lecture)
 Sunspaces (more details later in this lecture)
 Transpired Solar Collector
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Perforated metal wall covering
Solar energy heats up wall
Fan assists in drawing air through panels
Panels reject heat to air, heating the air before
introduction into building
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Solar Radiation: Shading
 Attempt to block solar radiation from impacting the building
during cooling season
 Devices can be:
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Natural or constructed
Fixed or variable (trees of differing types, movable shades,
etc.)
Opaque or somewhat transparent
Indoor or outdoor
 Categories/characteristics
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Overhang—panels or louvers, can be rotated
Fins/wings—panel(s), slanted or rotating
“Eggcrate”—reduced depth combined overhang/fin, slanted
or rotating
Roller shades/awnings
Trees/vines—free standing, trellis, “attached”
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Solar Radiation: General Shading
Guidelines
Exterior shading more efficient, but weather can take its toll on
mechanized variable systems that are outdoors
 South windows
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East/west windows
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Little shading required
Desirable and even diffuse daylight
Fins typically enough, if needed at all
Skylights can be problematic
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Difficult to shade due to low altitude angles
Fins (slanted) more effective or eggcrates
Trees best on the east, west, southeast, and southwest (northern
hemisphere)
North windows
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Easiest to shade, overhangs very effective
Fins may be needed for early morning, late afternoon
Trees typically not much help to the south
Potential for leaks is greater
Solar/light gain maximized at wrong time of year (summer)
Can be more difficult to shade
Other orientations may require combination solutions
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Alternate Cooling Techniques: Air
Movement
 Ventilation
 Comfort ventilation: increase comfort by increasing
air flow rates with the building
 Night purge ventilation: ventilate (naturally or
mechanically) at night when the outside air
temperature is presumably cooler than inside
 Technology
 Windows (various types of openings)
 Cool Towers (Down Draft Coolers)
 Thermal Chimney
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Alternate Cooling Techniques:
Roof Cooling
 Basic concept: block solar radiation during the day, then take
advantage of radiation to cold sky during the night (clouds will
significantly decrease nighttime performance)
 Roof Pond
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Simply a layer of water contained on a flat roof or
containers of water
Daytime operation
 Pond is covered with insulation to deflect solar heat and
reduce connection to outside environment
 Thermal mass of water soaks up heat from the interior space
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Nighttime operation
 Pond is left uncovered to reject heat from water to outside
environment
 Heat is rejected via convection to surrounding air and to sky
via radiation
 Cycle can be reversed in winter to provide a Trombe Wall type
roofing system
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Roof Pond: Drawbacks
Added cost of system and extra
maintenance
Movable insulation systems are
typically not very successful
Concerns about leaks
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Alternate Cooling Techniques:
Roof Radiator
 Similar in concept to roof pond, but replaces
water and movable insulation with a metal
deck that is elevated above the roof
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Can use interior movable insulation with a “closed”
deck
Can be fan assisted with an “open” deck
 Can be used as a heating system in winter if
solar energy is trapped between metal deck
and roof
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Hot air is then circulated to interior spaces
 Drawbacks
 Added costs of roof deck
 Reliability/longevity of movable insulation
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Roof Radiator: Cooling Operation
 Daytime operation
 Metal panel reflects a portion of the solar
radiation
 Insulation blocks heat transfer to building
interior
 Or ventilation air reduces heat transfer from
roof deck to actual roof
 Nighttime operation
 Roof radiates heat to sky
 Roof temperature may be low enough to
actually cool outside air even further
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Earth Coupling: Direct Earth
Coupling
 Underground or berms
 Ground temperatures can be lower than
outside air, making this a good heat sink
 Concerns about winter may require
insulation of ground and/or building
surfaces in contact with ground
 Potential moisture problems
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Earth Coupling: Indirect Earth
Coupling
 Buried supply air tubes
 Inlet air diverted through pipes that are buried
 Air is cooled by the cooler ground, providing some
free cooling
 Pipes must be buried significantly deep
 Maintenance and moisture issues
 Ground “micro-climate” change using
evaporation
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Cool the ground surrounding a building using
evaporation
Ground connected buildings
Elevated buildings
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EnergyPlus Modeling Capabilities
Thermal Mass
Trombe Wall
Sunspaces
Movable/transparent insulation
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Thermal Mass/Energy Storage
within Buildings: Theory
 Storage energy (heat) within building elements
(exterior or interior) for use or release at a later
time/date (analogy of a sponge or a rechargeable
battery)
 Building materials store heat as “internal energy”
 Thermal mass a function of material properties
(specific heat and density) as well as volume of
materialhow much thermal mass is “enough”?
 Energy stored in a building material will eventually be
release—either to the interior or exterior depending
on placement of mass, environmental conditions, etc.
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Thermal Mass: Examples
Traditional Examples
 Dense building types with very thick
walls
 Ice blocks from Lake Michigan
More Modern Examples
 “Trombe Walls”
 Interior Water Walls or Containers
 Phase Change Materials
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Thermal Mass: Seasonal Effects
 Cooling Season
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Dampen the effect of outside temperature variations
Shift time of highest cooling loads to the night hours
(offices)
Absorb excessive internal gains during daytime hours
(usually combined with night ventilation strategies)
 Heating Season
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Store solar energy absorbed for use during the nighttime
hours when temperatures are low and the sun is not visible
Avoid potential overheating problems due to excessive
direct solar gains
Note: thermal mass effects will not show up in a winter
design day run—must look at an annual simulation with
actual weather data
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Thermal Mass: Key Terms in
EnergyPlus IDF
Material:Regular—specification of
specific heat and density
Construction—reference to a
material layer definition
Surface—reference to a
construction definition
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Trombe Walls: Theory
 Primarily a passive heating element used to
delay the impact of solar radiation
 Intended to cooperate with direct gain
through windows to provide heating via solar
radiation during all parts of the day and night
 Most useful on south, southeast, and
southwest facades
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Trombe Walls: System
components
 Thermally massive wall (brick, concrete,
stone, water) painted a dark color to
absorb solar radiation
 Air gap
 Wall cover (transparent glass) to allow
sun light to get through to the thermal
mass and to block some of the heat loss
to the outside environment
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Open vs. Closed Trombe Walls
 Open System
 Similar to a mini-sunspace where the air in
the gap between the cover and the wall
mass is allowed to circulate to an interior
space
 More important if no visual link to the
outside
 These have fallen out of favor (in US) due to
difficulty in controlling the amount of
exchange between the air gap and the
attached space and due to the loss of delay
factor (easier to combine wall with
windows); also maintenance issues
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Open vs. Closed Trombe Walls
Closed System
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Air gap between the wall mass and
the cover is sealed
Heat is trapped and absorbed better
into the thermal mass
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Trombe Walls: Performance
 Best for heating when wall mass has both a
high storage capacity and a high thermal
conductivity
 High thermal conductivity increases heat
gain/loss of overall wall assembly
 Wall cover should be as transparent as
possible but also resistive
 Solar must be kept out of the Trombe wall in
summer through use of:
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Shading devices
Specialized transparent insulation materials
Electrochromic or thermochromic glazing
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Trombe Walls: Examples
 Trombe walls are usually but not necessarily
restricted to simple flat south-facing walls
(compare Zion National Park Visitor’s Center
to NREL Visitor’s Center)
Photos courtesy of www.nrel.gov
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Trombe Walls: Key Terms in
EnergyPlus IDF
 Material:WindowGlass—specification of window
properties
 Construction—definition of wall and window
constructions
 Surface—specification of wall and cover (separate) with
wall defined as an “interzone partition
 Zone—definition of Trombe Wall air gap as a separate
thermal zone
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Cover is specified as a window covering a fictitious exterior
wall
Trombe wall shows up in TWO zones (equal and opposite
interzone partition)
Zone definition must include syntax to use special Trombe
wall coefficients
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Trombe Walls: Example of
Trombe wall syntax (Zone)
ZONE, Lounge,
0.0,
10.0,
14.9,
0.0,
1,
1,
4.0,
0.0,
TrombeWall;
!!!!!!!!!!-
Zone
Zone
Zone
Zone
Zone
Zone
Zone
Zone
Zone
Zone
Name
North Axis (relative to Building)
X Origin {m}
Y Origin {m}
Z Origin {m}
Type
Multiplier
Ceiling Height {m}
Volume {m**3}
Inside Convection Algorithm
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Sunspaces and Double Skinned
Buildings
 Sunspaces and double skinned buildings can also be
modeled as separate zones
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Note that in EnergyPlus solar radiation will pass
through one space and into another but that once it
gets to the second zone it is assumed to be all
“diffuse”
Both sunspaces and double skinned buildings provide
an extra buffer from the outside
Sunspaces add potentially usable space
For systems which exchange heat through air
transport, definition of a MIXING or CROSS MIXING
statement required (not very accurate)
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Movable Insulation: Purpose
 Apply insulating layer to exterior (or interior)
of building that can be scheduled for various
times of day or year
 Intended to trap heat inside a building or
block heat from coming into a building during
certain times
 Many applications, but in reality, most of
these are not feasible due to complexity of
the systems
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Movable Insulation: Process
In EnergyPlus, movable insulation can
be applied to the interior or exterior
side of a surface (but not windows)
Window insulation must be specified as
window blinds
Exterior insulation may be transparent
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Movable Insulation: Syntax
 Insulation type: must be keyword “Interior” or
“Exterior”
 Surface name: surface that insulation will be
applied to (link to a surface definition within
the input file)
 Material name: composition/description of
material layer that makes up the insulation
(link to a material definition within the input
file)
 Schedule: when the movable insulation is
applied (link to a schedule definition within the
input file)
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Movable Insulation: Example
Example of IDD format and IDF:
MovableInsulation,
A1, \field Insulation Type ( Exterior or Interior )
A2, \field Surface Name (heat transfer surface to which insulation applied)
A3, \field MaterialMovInsul- Name of the material used for movable insulation
A4; \field SchedMovInsul-Schedule for movable insulation
Schedule controls if insulation is present and acts
as a multiplier on the R-value of the material
Material layer can be transparent if exterior insulation
MovableInsulation,
Exterior,
Zn001:Wall001,
MovableInsulationMaterial,
ON;
MATERIAL:REGULAR-R,MovableInsulationMaterial,Rough,2.0,0.9,0.7,0.7;
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Summary
 Careful attention to climate and building
heating and cooling needs as well as
knowledge of passive strategies can help
significantly reduce the amount of energy
consumed to condition a building
 EnergyPlus “green” building modeling
capabilities:
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Thermal Mass
Trombe Wall
Sunspaces
Movable/Transparent Insulation
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