1 Introduction
The document demonstrates using EnergyPlus to estimate a building’s energy consumption,
and based on the estimation, to optimize the building’s design parameters to improve its energy
efficiency. For demonstration purpose we study a single-zone welding shop’s building, aiming at
optimizing its envelope design parameters to minimize its annual energy consumption. First we will
give a formulation of the envelope design problem, and then we will give a tutorial on estimating
a given design’s energy consumption (using EnergyPlus), which is the emphasis of this
demonstration. Finally optimization method will briefly be introduced. For reference of the
motivation of our study and why we choose a welding shop as our case, please see Ref. [1] (note
that in this demonstration we only consider building energy consumption but not overall energy
consumption cost as in Ref. [1]).
2 A single-zone welding shop’s envelope design problem
Key features that significantly impact a building’s energy consumption include building
orientation, shape coefficient (the ratio between the external skin surfaces and the inner volume
of the building), window-to-wall ratio, heat transfer properties of the envelope surfaces (walls,
ground, roof and doors), and window glazing properties, etc. Here we only consider the first three
features, and other features are assumed to be known with given values. This corresponds to the
scenario of determining the building envelope layout with building construction materials been
selected.
We also assume that building’s shape being cuboid with a given height (decided by the
production requirement); building’s location, welding activities related configuration and the setpoints of inner environmental conditions are all given; two doors with same fixed size are located
on the one set of opposite walls; and windows with same fixed size are located, in pairs, on the
other set of opposite walls (number of windows is to be determined), as shown in Fig. 1.
The building orientation can be represented by the building azimuth, α, the building shape
coefficient is denoted as
cshape 
l  w  2H  l  2H  w  1 2 2  -1
    m ,
H l  w
H w l 
and the window-to-wall ratio is defined by
rwin / wall 
2n  Awin
A
n
 win 
2H  l  2H  w
H lw .
where H is the height of the building, Awin is the area of each window, and both of them are given;
l and w are the length and width of the building, respectively, and n is the number of windows in
pair.
Hence, to achieve an envelope design we should determine the values of the following four
variables:
α, l, w, n
The constraints include:
1) bound constraint on azimuth (considering the envelope symmetry)
0° ≤ α ≤ 90°.
2) bound constraints on length and width
Llower ≤ l ≤ Lupper,
max(Wlower, Wdoor) ≤ w ≤ Wupper,
where Llower and Lupper (Wlower and Wdoor, respectively) are the lower and upper bound of l (w,
respectively), and Wdoor is the width of the doors.
3) constraint on the number of windows
n·Wwin ≤ l – M, n ∈N
where Wwin is the width of each window and M is summation of pre-determined margin for
windows and necessary spaces between windows. N is the set of non-negative integers.
4) constraint on zone area
l·w ≥ Azone,
where Azone is the given low bound of zone area.
N
H
α
Awin
l
Hdoor
Wdoor
w
Fig. 1 Schematic of building design problem example
3 Simulation-based building energy consumption estimation
The above envelop design problem is not analytical and needs to be solved by simulationbased optimization methods. The precondition is we can estimate a given design’s “performance”
as the objective function value, i.e., a design’s resulted annual energy consumption. Once we can
do that, simulation-based optimization algorithms would help to find good designs. Here we give
firstly an energy consumption estimation framework, and then a tutorial on estimating the welding
shop’s energy consumption with a given envelop design.
3.1 Energy consumption estimation framework
Based on EnergyPlus simulation, we can estimate the welding shop’s building energy
consumption following the framework shown in Fig. 2. The framework applies to a class of plants
where the environmental conditions would not affect the production processes energy
consumption. The framework includes two steps:
(1) Calculate the schedules of the effects of the production processes on the environment
(internal gains of heat, moisture and contamination, etc.);
(2) Use EnergyPlus to estimate the building energy consumption with inputs including the building
design parameters, the weather information, the environmental conditions set-points and the
schedules calculated in Step (1).
Outer environmental condition data
Building’s design parameters
Inner environmental
condition
requirements
Production schedule
and shift pattern
Production process
parameters (workers’
parameters included)
Schedule of inner environmental
conditions (temperature, humidity,
light level, air quality, etc.) setpoints
2
EnergyPlus
simulation
1
Schedule of dissipation of heat,
moisture, air pollutant, etc. from
production process (worker’s
activities included)
Building energy
consumption
Fig. 2 Energy consumption estimation framework
3.2 Estimating the welding shop’s energy consumption
EnergyPlus uses an .idf file, which actually is a text file, as its input. With a text format and
good modularity, .idf file is easy to read and configure. Here we only mention the steps of getting
an estimation through but will not cover the file configuration details. For details of configuring
an .idf file and further information about applying EnergyPlus, please see Ref [2].
3.2.1 Preparing basic configuration input
Below is an .idf file containing necessary inputs except those related to the four design
variables listed in Section 2.
WeldingShop_BasicConfig.idf
This file contains basic configuration including the building’s location, constructions and materials,
inner activity related parameters, and simulation output requirements.
The single-zone welding shop is assumed to be located in Beijing (39.93°N, 116.28°E). Welding
activities related configuration and the set-points of inner environmental conditions are given as
the same as the numerical example used in Ref. [1]. The heating and cooling loads are assumed to
be satisfied at all time (an ideal loads air system is adopted in EnergyPlus simulation).
The walls consist of (listed from outside to inside) 2cm mortar, 20cm concrete and 3cm
insulation. The floor consists of 20cm concrete. The roof consists of 18cm concrete, 10cm
insulation. The doors consist of 0.5mm iron, 6cm insulation, and 0.5cm iron. The windows are 6mm
+ 3mm + 6mm low-emissivity double pane windows. The zone has day-lighting controls with two
illuminance set-points of 500lx on the median line along the length and at a distance of length/3
from each door, and at a height of 1m.
Other envelope related parameters are: H = 4m, Wdoor = 2m, Hdoor = 2m, Awin = 1.5m2, Wwin =
1m, Azone = 100m2, Llower = Wlower = 7m, Lupper = Wupper = 15m, and M = 5m.
3.2.2 Generating variable-related configuration input
For different designs of variables, different variable-related input configuration can be
generated. Below is a sample of the variables-related configuration:
WeldingShop_VariableConfig.idf
This file contains information of the building orientation, the size of the building walls, doors and
windows, and the location of the doors and windows on the walls. Also daylight control
configuration is included in this file because the position of its reference points are related to the
layout the building envelop.
3.2.3 Obtain a complete input file
Merging the above two parts of configuration information we can obtain a complete input .idf
file as
WeldingShop.idf
Note that in a common EnergyPlus simulation we don’t have to obtain an .idf file by merging two
parts. Here, because we may want to fix part of the whole configuration and to change only the
variables-related configuration, maintaining a basic configuration file and just generating variablerelated configuration files may be a good way for programming.
3.2.4 Preparing weather data file
To run an EnergyPlus simulation for certain weather condition, a weather file corresponding
to the building location is needed. Weather files for different locations can be downloaded on
EnergyPlus website (Ref. [2]). Here we paste Beijing’s CTYW (Chinese Typical Year Weather)
weather data, which is used in Ref. [1] case study.
CHN_Beijing.Beijing.545110_CTYW.epw
3.2.5 Running EnergyPlus
Now we can run EnergyPlus simulation with the .idf file and the weather file. There are two
ways of running the simulation. The first way is by EnergyPlus’ simulation launch user interface EPLaunch. For tutorial please see EnergyPlus’ Getting Started document (in the Documentation
directory of EnergyPlus installation). While, here we recommend the second way of executing
EnergyPlus with a command. In this way we can automatically run simulations if we have a number
of different .idf files (corresponding to different designs) to evaluate. The command is:
RunEplus.bat WeldingShop CHN_Beijing.Beijing.545110_CTYW
where RunEplus.bat is a batch file in the installation directory of EnergyPlus, which calls EnergyPlus
to run simulation with the files specified by its following arguments (the two file names without
suffix) as its inputs; the .idf file should be in the same directory with RunEplus.bat; the weather
data file should be in the WeatherData directory in the same directory with RunEplus.bat. The
argument strings “WeldingShop” and “CHN_Beijing.Beijing.545110_CTYW” should
correspondingly be changed if an .idf or weather data file with a different name is used.
3.2.6 Checking the results
After a successful run (the generated WeldingShop.err file says no error), one can check the
simulation results saved in the WeldingShop.eso or WeldingShop.csv file generated (same data but
different format). We paste here the results from the .csv file below, from which we could calculate
the overall annual energy consumption is:
2.15*109J + 3.57*109J + 7.00*109J = 12.73*109J = 3536.09kWh
WELDINGZONE
Date/Time
LIGHTS:Lights Electric
Consumption
[J](RunPeriod)
simdays=365
2154626758
WELDINGZONE:Zone/Sys
WELDINGZONE:Zone/Sys
Sensible Heating Energy
Sensible Cooling Energy
[J](RunPeriod)
[J](RunPeriod)
3574474913
7000822197
4 Building energy efficiency optimization
Now that we can run EnergyPlus to evaluate different designs automatically (by a command
line manner). With the EnergyPlus-based simulation as an objective function value estimation tool,
simulation-based optimization algorithms can be applied to search for optimal or approximate
optimal designs. Such algorithms include Genetic Algorithm, Simulated Annealing or Ordinal
Optimation, etc. For further information please see Ref. [1].
Reference
[1] Liu H, Zhao Q C, Huang N J, Zhao X. A simulation based tool for energy efficient building design
for a class of manufacturing plants[J]. IEEE Transactions on Automation Science and Engineering,
2013,10(1):117-123.
[2] EnergyPlus website. http://apps1.eere.energy.gov/buildings/EnergyPlus/.