Transcript EnergyPlus Training Part 1

Lecture 7: Building Modeling
Questions
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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Potential Questions You Might
Have
Is every room a zone? How many
zones?
How detailed should the building model
be?
How accurate will my results be?
Do I need to do a design day run or an
annual run?
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Defining a Building
Getting Started Manual

A methodology for using EnergyPlus
Four Step Process

Gather information

Zone the building

Create building model

Create input file
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Step 1 - Gather Information
 Location and design climate
 Building description
 Wall constructions
 Wall sizes
 Window, door, overhang details
 Wall locations (shading)
 Building use information
 Equipment and occupancy information
 Schedule information
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Step 1 - Gather Information
(cont’d)
Building thermostatic controls
HVAC equipment information

Equipment types

Operating schedules

Control information
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Step 2 – “Zone” the Building
Thermal, not geometric, zones
Heat storage and heat transfer surfaces
Heat transfer  only when expected to
separate spaces of significantly diff
temps

Exterior Walls, Roofs, Floors
Heat storage surfaces  surfaces
separating spaces of same temperature
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Simplifying EnergyPlus Input
Simplify -- Think before typing
Layout simple floor plan
As few zones as necessary
As few surfaces as necessary
Surfaces, NOT volumes
Is shading important?
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As Few Zones As Necessary
Combine similar zones
Use zone multipliers wisely
Combine vertically and horizontally
10 ZONES OR 6 OR 4 OR 2?
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Rules of Thumb Reminder
One zone per major exposure minimum
Separate zones for different uses
Separate zones for different setpoints
Separate zones for different fan systems
(and radiant systems)
Do not use “rooms” to determine zones
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Step 3 - Create Building
Model
Heat transfer and heat storage surfaces
Define equivalent surfaces
Specify construction elements
Compile surface and subsurface info
Compile internal space gain data
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As Few Surfaces As Necessary
Combine similar surfaces
Combine small surfaces with larger
surfaces
Ignore minor details
Use internal mass
7 WINDOWS OR 3?
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Step 4 – Create Input File
Materials and Constructions
Building Geometry
Internal Loads
Special Features
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Case Study
 US Army Fort Monmouth education center
 Temperate coastal climate, Near New York
City
 Floor area of over 13,000 sq.Ft.
 Building height of 10 ft.
 Total window area in excess of 1,400 sq.Ft.
 May serve as many as 200 people
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Ft. Monmouth Floor Plan
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1
2
24
25
22
26
21
20
3
19
4
5
6
12
9
10
18
11
17
13
7
14
15
16
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How many zones should there be?
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Option 1: One-Zone Model
50 ft
39 ft
(62 ft2)
65 ft
10 ft
(334 ft2)
20 ft
65 ft
20 ft
(113 ft2)
75.3 ft
(209 ft2)
124.6 ft
(84 ft2)
34 ft
(26 ft2)
(82 ft2)
(363 ft2)
16 ft
(42 ft2)
(61 ft2)
50 ft
43.3 ft
101 ft2)
(40 ft2)
113 ft
How accurate is this model?
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Option 2: Six-Zone Model
Five fan systems or zoning thermally
Expect higher solar on south and west
Zone 1
Zone 2
Zone 4
Zone 6
Zone 5
Zone 3
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Modeling Fort Monmouth
with EnergyPlus
 With appropriate detail:
 EnergyPlus can convert a simple model into a
powerful energy analysis
 Complex interactions modeled for an entire year
 Designers can then:
 Size systems and plants
 Examine performance of various system and plant
configurations
 Determine more efficient operational schemes
 Calculate annual energy consumption
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Six-Zone Model Loads
90
80
Cooling Load [kBtu/Hr]
70
Zone 1
60
Zone 2
50
Zone 3
40
Zone 4
Zone 5
30
Zone 6
20
10
0
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Ho urs
How does this compare to 1-zone model?
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Comparison Between
One and Six-Zone Models
300
Cooling Load [Kbtu/hr]
250
200
1 Zone Cooling
150
6 Zone Cooling
100
50
0
1
3
5
7
9
11
13
15
17
19
21
23
Ho urs
Difference in Total Cooling Load < 10%
Difference in Total Heating Load < 1%
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Simple EnergyPlus Model
Produces Incredible Results
 Why? EnergyPlus captured the physics ...





Building exterior remains the same
Solar load equivalent
Internal loads unchanged
Internal mass accurately approximated
Identical weather conditions
 Difference: unconditioned spaces
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Detailed Model Benefits
Improved accuracy
Better resolution of loads for system
sizing
Incredible analytical power
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Another Aspect to Consider ...
 How much of an effect does the thermal mass
of zone surfaces have on zone loads?
 Comparison using Ft. Monmouth six zone
model


Standard EnergyPlus run
EnergyPlus run using no thermal mass (R values)
 Use output reports from previous run to
change the surface definitions to R values
only
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Key Physical Properties
 Exterior Walls




4” Dense Face Brick
8” Heavyweight Concrete
Block
6” Mineral Fiber
Insulation
5/8” Gypsum
 Roof




3/4” Roofing
2” Expanded Polystyrene
Insulation
Airspace
3/4” Acoustic Tile
 Slab on Grade Floor


4” Concrete
Tile Flooring
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Case 1:
Thermal Mass Effects
 Cooling loads higher
with no mass


Total load off by 14%
Peak off by 15%
 Larger differences show
up in zones 1, 2, and 3

Could result in oversizing
of systems and plants
 Only thermal mass
changed

Other EnergyPlus details
a factor
Cooling Loads
No-Mass vs. Mass
Zone
Total
Peak
1
12%
32%
2
16%
31%
3
16%
40%
5
14%
16%
6
15%
14%
All
14%
15%
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Design Day Calculations
Convenient short time period
Established design day conditions easy
to obtain
Fairly good estimate for system and
plant sizing
Will design day results be an accurate
indication of long term trends?
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Case 2:
Adding Roof Insulation
What will the effect of doubling the
amount of roof insulation be?
Roof




3/4” Roofing
2” Expanded Polystyrene Insulation
Airspace
3/4” Acoustic Tile
Will a design day tell the whole story?
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Design Day
Heating Load Results
400
Heating Load [Kbtu/hr]
350
300
4in Insulation Roof
2in Insulation Roof
250
200
150
1
3
5
7
9
11
13
15
17
19
21
23
Ho urs
Daily Decrease for Heating Loads = 8%
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Design Day
Cooling Load Results
Cooling Load [Kbtu/hr]
300
200
4in Insulation Roof
2in Insulation Roof
100
0
1
3
5
7
9
11
13
15
17
19
21
23
Ho urs
Daily Decrease for Cooling Loads = 3%
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Annual Run Building Loads
Why are the cooling loads higher with
more insulation?
Mild summer + High MRT =
High summer heat retention
Overall reduction in loads, but not as
expected from design day results
Heating
Load
Cooling
Load
Peak
Heating
Peak
Cooling
Total
Loads
Cheap Roof
468000
147500
588
289
615500
Better Roof
417700
150700
561
282
568400
Annual Diff's
10.75%
-2.17%
4.66%
2.42%
7.65%
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Let's Change the Weather. . .
 Champaign, Illinois
 Temperate inland climate, south of Chicago
 Compare increased roof insulation
 Design day heating and cooling loads both
decreased
 Annual building loads also decreased
 EnergyPlus "changed" the weather for every
hour of the year
 EnergyPlus never forgets the physics!
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Summary
Simple models can produce good results
Thermal mass can have a significant
effect on loads
Design day calculations can be
misleading
Annual runs pick up mild weather
effects
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