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Interface Development for preparing data file into EnergyPlus software

Pedro Miguel Vedor Carrelha*

*Department of Mechanical Engineering, Instituto Superior Técnico,

University of Lisbon, Av. Rovisco Pais 1,

1049-001 Lisboa, Portugal; e-mail: pcarrelha@gmail.com

Abstract: This project has the main goal of creating an EnergyPlus pre-processor, which is a user friendly

tool that allows to generate dynamic simulation models for the Alameda Campus of Instituto Superior

Técnico buildings, converting available information from the DesignBuilder and the AUDIST file.

The pre-processor was programmed in MS Excel (.xlsm) with a permission of reading and writing

MACROS. Its structure consist in seven worksheets where the equipment/occupation data is inserted,

modified and erased and five VBA modules with sub-routines that allows to consult and read the information

from the audit files.

The building geometry was exported from existing DesignBuilder models. The information about the type

of equipment installed in each space, its operation schedule and the occupation in each zone was taken from

a program, the AUDIST, developed by the “Campus Sustentável” project audit team.

The program makes the connection between the existing geometry and the audit data creating a final model

in EnergyPlus ready to simulate. The Mecânica III building was chosen to be the demonstration example

to show how the pre-processor works and to confirm the model. The electric energy consumptions from the

simulation were desegregated, analyzed and compared with the billed consumptions. The mean total

deviations obtained were less than 10% confirming the model and the program created. Key-Words: Pre-processor, EnergyPlus, DesignBuilder, dynamic simulation of buildings, energy consumption.

1. INTRODUCTION

The increasing of world population combined with the industrialization has led to a growth in the electric

energy consumption. A significant part of this consumption is associated with building, where the type of

construction or the low efficiency of the installed equipment cause a waste of energy. So, to decrease this

waste is important to apply energy efficiency measures.

Driven by this need of decreasing the input energy, the introduction of mathematical models of buildings

can be an asset when analyzing its consumption. With this models we can make a preliminary analysis

without making many measurements and we can apply energy conservation measures (ECM) to buildings

in order to reduce its consumption without spending much time doing calculations.

1.1 Electric Energy in Portugal

From the year 2000 until 2010, Portugal electric energy consumption increased almost linearly reaching its

maximum in 2010, registering a value of 50.612 GWh [1]. In the following two years the consumption has

been declining gradually, reaching 47.000 GWh [1] in 2012. This reduction comes, probably, from the

economic crisis that Portugal is facing and the impact of adopted energy efficiency measures. From the total electric energy consumption it is possible to see that 57% [1] comes from all the buildings

in Portugal (around 3.600.000 buildings [2]) and 4% of this values comes from Portuguese State buildings.

So implementing ECM strategies can bring advantages like the reduction of the country costs.

Despite the reduction of the consumed energy, the country energy dependence from external entities, the

use of fossil fuels for production of electricity and the emissions of greenhouse gases are still rising. So,

continue to invest in energy efficiency measures to reduce the consumption can bring advantages both to

the environment and to the economy. This work fits as a tool to support the study of the impact of these

measures through the use of mathematical models in buildings.

1.2 Electric Energy in Instituto Superior Técnico (IST)

Project Campus Sustentável

The IST is developing a project called “Campus Sustentável” [3] which runs under the Initiative Energy of

IST. The main goal of this project is to increase the buildings sustainability of the University Campus by

focusing on improving energy and hydro efficiency from its installations.

The first activity developed in this project consisted in an exhaustive inventory of all energy using

equipment installed and the study of the occupation pattern for all the buildings in Campus.

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In addition to that the team of “Campus Sustentável” in partnership with the managers of the buildings,

with the Maintenance Team and with the Construction Team of IST achieved a reduction in the consumed

electricity of 12,3% [4], in the biennium 2012/2013 over the previous year.

Actual Situation The IST Alameda Campus has an area of 107.149 m2 and is constituted by 26 independent building, whose

constructions vary widely with ones from the 30’s and others fairly recent. Also, there are 12.311 users [4]

in the Campus that are contribuing directly to energy consumption (water, gas, electricity) and to the

thermal balance in each space (they generate heat).

The team from “Campus Sustentável” concluded that IST campus in Alameda/Lisbon is characterized by

an annual electricity consumption of around 15 GWh [4] and a typical load diagram has a nearly permanent

level of 1 MWh/day [4], to which is added all the campus activity.

Chart 1 - Annual consumption of electric energy of all IST buildings [4]

From Chart 1 it is possible to see that de general consumption is different from one building to another,

having several cases of small buildings using more energy per unit area than the larger ones. The Informatic

Pavilion is one of this cases (1.664 m2), consuming 100 kWh/m2.year, while the North Tower building

(9.367 m2) is consuming only 75 kWh/m2.year. This difference can be explained by the time of construction

of each building and the type of equipment installed in it (eg. Poor efficiency due to age of the equipment,

hours of operation and use). With this analysis is possible to see what buildings have more improvement

margin and whose modeling can potentially contribute to the overall objectives of increasing the energy

efficiency of IST.

1.3 Mathematical Models of Building Operation Simulation software’s can be used to help implementing energy efficiency measures in buildings. Currently

a variety of 3D buildings modeling programs are available in the market with different characteristics.

Although the characterization of the building is a very important feature, the diversity of interest quantities

(eg. Energy consumption, CO2eq emissions, inside temperatures) that can be selected are also a major point

to have in consideration when choosing a program to work with. The software needs to have a range of

possible outputs so the user can change the installed systems or introduce new systems and obtain the result

of these modifications.

One of the software’s used in the present work was the DesignBuilder, which has the advantages of being

very good for modelling buildings in 3D and for allowing to export the model into EnergyPlus

automatically. The license already acquired by the “Campus Sustentável” project, the existing geometric

models of all IST buildings created in this software and the compatibility with EnergyPlus were the main

reasons why DesignBuilder was chosen.

EnergyPlus was selected because it is the best software in open souce available on the market and because

of its good calculation capacities in terms of energy analysis and thermal load simulation of buildings,

based on the geometry and on the components installed in it. The program allows the user to select several

quantities of interest and has a large range of HVAC system for possible characterization. Also, being open

code allows the user to insert and modify new systems.

1.4 Thesis Objective

The main goal of this dissertation was to create a Pre-Processor of Energyplus, i.e. a user friendly tool that

allows to generate dynamic simulation models of buildings from other software’s and data bases. To

accomplish that it was exploited the work already done in DesignBuilder to define the geometry of the

building and all the information collected by the IST audit team stored in the AUDIST [5] file to complete

the building with the equipment installed and with the occupation of each space.

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Figure 1 - Structure of the generation process of EnergyPlus models

2. METHODOLOGY

The functioning process of the pre-processor can be divided in two stages. One concerning the conversion

of the building geometry model from DesignBuilder to EnergyPlus. The second phase is related with the

transformation and processing of the information from the AUDIST file to the EnergyPlus.

2.1 Geometry

All buildings from Alameda Campus of IST are modeled in DesignBuilder containing the structure with

the partitions, the windows and all the surrounding details for each space. However, the equipment and the

people defined in these models were not consistent with the real building due to limitations of the software

but also who created the files wanted a general model instead of a very detailed one. Because of these

differences was decided that the DesignBuilder files would only retain the geometry of the buildings being

the remaining information deleted.

In order to get an accurate geometry model into EnergyPlus is necessary to follow a series of simple

procedures. First it is necessary to analyze the model in order to confirm if all the spaces are well defined

and to deselect some options automatically selected by the program. Than all the devices and the people

defined in it need to be deleted and the names of thermal zones must be changed so the pre-processor can

link the equipment from AUDIST with the right zone. After completing this steps the model can be exported

to EnergyPlus, finishing the first phase of the process.

2.2 Devices and Occupation

The model conversion from EnergyPlus to DesignBuilder generates only one file with the geometry data

of the building, for this reason all the information about the systems installed in each zone must be entered

using the AUDIST and the pre-processor.

2.2.1 AUDIST Structure

This file was developed by the “Campus Sustentável” team, whose methodology is described in [3], and

aggregates all the available data related with the devices installed in IST buildings. The AUDIST is in MS

Excel format and is divided into seven worksheets. The names and the type of data defined in each

worksheet and the parameters used by the pre-processor to complete the model are explained below:

“Ocupação” – Aggregates all the information about the occupation of each room. The pre-processor

use the type of space (office, laboratory, etc), the number of people that normally works in that space and

the time they spend there.

“Iluminação” – Gather all the data about the lighting systems installed in each space. The parameters

used are the total absorbed power (W), the percentage of utilization and operation schedule for each lighting

system.

“Informática, EPI, Catering” – Gather all the information about the informatics, the plug-in and the

catering equipment installed in each space. The pre-processer uses the total absorbed and standby power

(W) and the operation schedule for each device.

“AVAC-Local” – Aggregates the data related with the HVAC systems not centrally powered or whose

functioning cannot be controlled by the campus technical services. The parameters used are the electric and

thermal power for cooling and heating (W), the coefficient of performance (COP), the number of devices

installed in each space and the operation schedule.

“AVAC-Comum” – Gather the data related with the HVAC systems centrally powered and the pre-

processer uses the electric and thermal power for cooling and heating (W), the coefficient of performance

(COP), the number of devices installed in each space and the operation schedule.

For each worksheet the program uses the “PisoId” and the thermal zone of each space to define where to

put the people and the equipment.

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2.3 Pre-Processor Structure

The program developed in this work is in MS Excel format (.xlsm [6]) with a sequence of commands and

functions stored in VBA modules that can be used for repetitive tasks, automating them. The pre-processor

structure consists of seven worksheets, where the equipment data is inserted, modified and deleted and five

VBA modules with routines and functions that allow to read, transform and copy the information from the

AUDIST. They also allow to convert the information into the required format and to export it to a file

readable by EnergyPlus. The names and the type of data defined in each worksheet are explained below:

Start – Only used for showing the initial menu.

IDF – Store all the information generated in the final format and copy it into a file readable by

EnergyPlus.

Report – Worksheet where is written a report with the hourly, daily, weekly and annual electric energy

consumption of the lighting system and the informatics, plug-in and catering equipment.

People – Store all the information about occupancy schedules and number of people in each space, in

its final format.

Lighting – Store all the information about the operation schedule, the powers of the lighting system and

the electric devices.

HVACcomum – Retain the data related with all HVAC systems both local and common, already in its

final format.

Templates – Contain templates with the occupancy/operation schedule and the type of metabolic rate.

It is going to be use by the People and Lighting Worksheets.

The entire process can followed from the flowcharts of Figures 2 and 3.

Figure 2- EnergyPlus Pre-Processor Scheme

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3. DEMONSTRATION EXAMPLE

3.1 General Characterization of the Building

The chosen building to test the pre-processor was the Mechanical Engineering III. It was built and equipped

in the XXI century being a recent structure compared with the other buildings in Campus. The edifice has

four levels two high (3 and 4) and two buried (1 and 2) and the building can be access by the main entrance,

which is in the southern part of the third floor.

In terms of building envelope, the characterization of the opaque building elements (walls, floors and roofs)

and the translucent (glazed areas) are presented in Tables 1 and 2.

Figure 3 - Flowchart of the Pre-Processor operation

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The local and the common HVAC systems installed in the Mecânica III building are characterized in the

Tables 3 and 4.

The lighting systems and all the informatics, plug-in and catering devices are characterize in the Tables 5,

6 and 7.

Table 1 – Walls, Roof and Ceiling Materials (Opaque) [7]

Table 2 - Window Materials (Translucent) [8]

Table 5 - Lighting Systems installed in Mecanica III [8]

Table 6 - Informatics equipment installed in Mecanica III

[8]

Table 7 - Plug-in and Catering equipment

installed in Mecanica III [8]

Table 3 - Characterization of Local HVAC Systems installed in

the Mecânica III [8]

Table 4 - Characterization of Common HVAC Systems

installed in the Mecânica III [8]

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3.2 Results

After the creation and parameterization of the model in EnergyPlus, simulations were performed in order

to compare the results obtained with the values presented in the AUDIST file and in the ENERGIST [9]

platform, to confirm if the model is as close as possible to reality. The quantities of interest selected to

compare were the electric energy consumption by type of equipment (Lighting, HVAC, Informatics, Plug-

in and Catering) and the total consumption of the building.

3.2.1 Dynamic simulation DesignBuilder

Initially, the electric consumption from the already existing models in DesignBuilder were compared with

those present in the AUDIST.

For the lighting systems, the minimum deviations found were 5% and 7% for thermal zones (TZ) 6 and 11

and 557% for zone 13. The average total deviation was 63% and the electric consumption 2370 kWh/year.

Nevertheless, these results show that the lighting systems are poorly defined in the model. For the electric

power consumers, such as informatics, plug-in and catering equipment, the differences found vary widely,

having thermal zones like 21 and 22 with a deviation of 2% and like 11 with a value rounding the 4500%.

The average total deviation is 60% and difference between consumptions is over 35.834kWh/year.

Table 8- Total electricity consumption for HVAC systems generated by AUDIST and by DesignBuilder

For the HVAC systems introduced in the DesignBuilder model only the AHU (Air Handling Units) were

defined. As it can be seen in the Table 8, the lack of equipment resulted in a huge difference for the annual

consumption, 99.172 kWh/year, when compared with the AUDIST values.

With the results obtained in these simulation, it is possible to support the decision of using only the building

geometry from the existing DesignBuilder models.

3.2.2 Dynamic simulation EnergyPlus

The Table 9 and Charts 3 and 4, illustrate the values obtained from the new building model simulation in

EnergyPlus created by the Pre-Processor, in order to show the improvements made. The results are going

to be compared with the values presented in the AUDIST file.

For the lighting systems the maximum deviation obtained, when compared with AUDIST, was 10% for

thermal zone 4 and the minimum was 1% for zones 5, 8 and 9. The average total deviation was 3%, being

the difference between the total consumption of 980 kWh/year. Regarding the electricity consumption for

the informatics, plug-in and catering equipment, the maximum deviation obtained was 14% for zone 56

and the minimum was 1% for zones 2 and 27. The average total deviation found was 6% and the

consumption difference was 169 kWh/year, which is a low value given that the total value for this

Chart 2 - Magnitude of the difference in the electric

consumption for the lighting systems (EPlus/AUDIT)

Maximum TZ- 4 Minimum TZ - 5, 8 and 9

Chart 3 - Magnitude of the difference in the electric

consumption for the electric equipment (EPlus/AUDIT)

Maximum TZ- 56 Minimum TZ - 2 and 27

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equipment is 40.000 kWh/year. These discrepancies appears because of the process done by the pre-

processor when grouping different spaces belonging to the same thermal zone.

Table 9 - Annual electric energy consumed by the local HVAC systems (AUDIST/EnergyPlus)

Table 9 shows the electricity consumed by the HVAC systems whose operation depends on the user. The

maximum deviation found was 100% due to limitations of the EnergyPlus, being one the inability to define

certain equipment like dehumidifiers and the other the impossibility of defining two different HVAC

systems in the same zone. This problem occurs, for example, in the thermal zone 27, which has an oil heater

and at the same time has multiple VRV indoor units. To solve this problem, the oil heater is consider as it

was turned off. Without this cases, the maximum deviation was 15% for zones 15 and 16 and minimum

deviation was 1% for the split unit installed in the zone 32. The average total deviation found for the total,

without the turned off systems, was 8% being the consumption difference of 358 kWh/year.

Table 10 - Annual electric energy consumed by the common HVAC systems (AUDIST/EnergyPlus)

The comparison of the total values for the centralized HVAC systems between the AUDIST and

EnergyPlus, are presented in Table 10. The minimum deviation obtained was 0.1% for the Air Handling

Unit installed in the thermal zone 4 and the maximum was 24% for the multiple VRV indoor units installed

in the zone 33. The average total deviation found was 9% and the difference between the total electricity

consumed was 5.670 kWh/year, not very significant given that the total was 121.786 kWh/year.

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Chart 4 - Comparison of monthly electric consumption between the ENERGIST and EnergyPlus

From the values shown in Chart 4, is possible to observe the discrepancies between the consumption

generated by the EnergyPlus model and the ENERGIST platform. The maximum deviation found was 25%

in July and the minimum was 0.1% in February. These maximum value can be justified by punctual

situations, like events or seminars, which are not consider in the AUDIST file. In energy audit it is stipulated

that if the global deviation value obtained is less than 10%, then the simulation is valid. Since the average

total deviation found was 7,5%, it is safe to say that the simulation is valid and, therefore, the model.

Finally a comparison between the total consumption provided by all the programs/databases used in the

present work is shown in Chart 5.

Chart 5 - Comparison of the annual electric consumption for all the different programs used

From Chart 5 it is possible to observe that the energy consumption for the first three are less than 5%, being

the difference between the EnergyPlus final model and the AUDIST of 13.420 kWh/year and between the

final model and the ENERGIST of 1.648 kWh/year. Since this values are less than 10%, it is possible to

say that the final model is very close to the dynamics of the real building, confirming that the pre-processor

works correctly and supporting the selection of EnergyPlus to create the final building model.

4. CONCLUSIONS AND FUTURE WORK The main goal of this work was accomplished. It was created a pre-preprocessor that combines the IST buildings geometry models in DesignBuilder with the information available in the AUDIST file, generating in the end a final EnergyPlus model very similar to the real building. In terms of functioning, the pre-processor developed in this dissertation, as a converting tool for EnergyPlus brings some advantages. With this program, defining the consuming energy systems became automated taking only few minutes to fill out an entire building, like Mecânica III, while if done manually would take a few hours. Besides that, it allows to create occupation/operation schedules for each space and to define most of the standard HVAC systems, requiring only a few properties of the equipment. Being an open code it allows the user to continue adding equipment and improving the program. As a demonstration example it was chosen the Mecânica III building from IST Alameda Campus to convert into EnergyPlus using the pre-processor. The model was simulated and the electric energy consumption was collected for comparison with the total billed or with the values provided by the AUDIST. For the lighting systems, it was found an average total deviation of 3% and a difference in the annual consumption of 980 kWh. The average total deviation for the informatics, plug-in and catering devices was 6% and a difference in the consumption was 169 kWh/year. For HVAC systems the results were divided in local and common, being the average total deviation found of 8% and 5% and the consumption difference of 348 kWh/year and 5670 kWh/year respectively.

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The monthly electric consumption generated by the model was compared with the values read in the ENERGIST platform. The minimum and maximum deviations were 0,1% and 7,5%, for the months of February and July. The maximum value obtained can be justified by punctual situations, like events or seminars, which are not consider in the AUDIST file. Finally, it was compared the annual consumption between all the programs used. The global deviations between the final model in EnergyPlus and the other two programs (AUDIST/ENERGIST) were less than 5%. In energy audit, it is stipulated that if the global deviation value obtained is less than 10%, then the simulation is valid. Since the average total deviations found were lower than this value, it is safe to say that the simulation is valid and, therefore, the model created by the pre-processor. Following the present dissertation one improvement is propose to extend the program areas of use. The suggested measure is to create a script, i.e. an extension of the pre-processor that allows the user to develop sensible, optimization and UQ studies. This add-in would force the EnergyPlus to run several simulations, modifying in each one the value of the selected parameter and in the end would generate the results for all the simulations made. With these values the user could see the changes made by the variation of the chosen parameter and could pick the most advantageous one for the system optimization.

5. REFERENCES

[1] PORDATA. Consumo de energia elétrica: total e por tipo de consumo,

http://www.pordata.pt/Portugal/, 2014.

[2] PORDATA. Edifícios segundo os Censos: total e por época de construção – Portugal, http://www.pordata.pt/Portugal/ 2014.

[3] de Matos, Mário; Toste de Azevedo, João & Ferrão, Paulo. O projeto Campus Sustentável e a

redução da fatura energética do Instituto Superior Técnico, 2014.

[4] Toste de Azevedo, João; de Matos, Mário & Ferrão, Paulo. Artigo PCEEE2014: Eficiência

Energética como Fator de Competitividade, 2014.

[5] Campus Sustentável. AUDIT_IST_v1.5.xlsm, 2014.

[6] Microsoft Support Excel 2013, https://support.office.com, 2014.

[7] Campus Sustentável. Envolvente Opaca e Translúcida Pavilhão Mecânica III – Soluções Gerais.xlsx,

2013.

[8] Campus Sustentável. Relatório de Auditoria Energética (Elétrica) e Medidas de Racionalização

Energética, 2013.

[9] Campus Sustentável. ENERGIST - energist.ist.utl.pt, 2012.