Building Energy Simulation Program Research Articles

Simulation of the Thermal Behaviour of a Building Retrofitted with a Green Roof: Optimization of Energy Efficiency with Reference to Italian Climatic Zones

Abstract Running a building energy simulation program (EnergyPlus), simulations were conducted on a ‘public housing’ building type, in order to evaluate the energy savings achieved by a green roof coupled with different configurations of external wall. EnergyPlus enabled the investigation of the thermal behaviour variations of the building envelope, and the possible consequences, in terms of comfort, on the temperature of the internal spaces. The variation of the energy behaviour of the building envelope type was assessed primarily through the analysis of the operative temperature T ° of the elements of surface casing, the trend of the surface heat fluxes on the faces of the elements of internal and external housing, the variation of the operating temperature inside the rooms. The energy savings achieved with a green roof varies considerably in relation to the reference performance obtained without this kind of insulating structure. The main parameters, useful to define the contribution of the green roof to the reduction of the loads of cooling plants, consist of the specific climate and the thermal isolation level of the initial coverage.

Computation and field experiment validation of greenhouse energy load using building energy simulation model

Greenhouse Building Energy Simulation (BES) models were developed to estimate the energy load using TRNSYS (ver. 16, University of Wisconsin, USA), a commercial BES program. Validation was conducted based on data recorded during field experiments. The BES greenhouse modeling is reliable, as validation showed 5.2% and 5.5% compared with two field experiments, respectively. As the next step, the heating characteristics of the greenhouses were analyzed to predict the maximum and annual total heating loads based on the greenhouse types and target locations in the Republic of Korea using the validated greenhouse model. The BES-computed results indicated that the annual heating load was greatly affected by the local climate conditions of the target region. The annual heating load of greenhouses located in Chuncheon, the northernmost region, was 44.6% higher than greenhouses in Jeju, the southernmost area among the studied regions. The regression models for prediction of maximum heating load of Venlo type greenhouse and widespan type greenhouse were developed based on the BES computed results to easily predict maximum heating load at field and they explained nearly 95% and 80 % of the variance in the data set used, respectively, with the predictor variables. Then a BES model of geothermal energy system was additionally designed and incorporated into the BES greenhouse model. The feasibility of the geothermal energy system for greenhouse was estimated through economic analysis. Keywords: greenhouse, building energy simulation (BES), energy load, dynamic analysis, geothermal energy, heating load DOI: 10.3965/j.ijabe.20150806.2037 Citation: Ha T, Lee I B, Kwon K S, Hong S W. Computation and field experiment validation of greenhouse energy load using Building Energy Simulation model. Int J Agric & Biol Eng, 2015; 8(6): 116－127.

단열 기준에 따른 기둥-보 목조주택의 단열 상세 및 에너지 성능

국립산림과학원에서는 한옥의 전통건축기술을 바탕으로 한국형 기둥-보 목조주택인 ?그린 프로젝트를 2006년부터 진행해오고 있다. 최근에는 에너지 절약 기술요소를 적용하여 건물의 에너지성능을 개선하고자 하였다. 본 연구에서는 강화된 단열기준에 따른 기둥-보 목조벽체의 단열상세를 제시하고 그에 따른 건물 에너지 절감 효과를 평가하고자 하였다. 건물외피의 열관류율은 현행법 수준과 저에너지주택인 패시브하우스 수준인 두 단계로 나누었으며 건물에너지 성능을 평가하기 위하여 건물의 기밀성능은 국내 신축 목조주택 수준인 <TEX>$3.0h^{-1}$</TEX>과 패시브하우스 수준이 <TEX>$0.6h^{-1}$</TEX> 두 단계로 나누어 열관류율과 기밀성능의 조합에 따라 4가지 경우에 대한 건물에너지 성능 평가가 이루어졌다. 대상건물은 서울에 위치하였으며 에너지 성능은 상용 건물에너지성능 평가 프로그램인 CE3가 사용되었다. 강화된 열관류율에 따라 시뮬레이션을 진행한 결과 연간 난방에너지 요구량은 <TEX>$14kWh/(m^2{\cdot}a)$</TEX> 절감효과를 나타냈다. Han-green project, which pursues Korean style post and beam timber house with traditional construction technique of Han-ok, has been carried out in KFRI (Korea Forest Research Institute) since 2006. Recently, the improvement of its building energy performance was studied with energy-saving elements. This study was conducted to provide the insulation details of building envelopes in a post-beam timber house for recent enhanced insulation standards and following effect on building energy performance. The level of thermal transmittance (U-value) values of building envelopes was composed of two stages: present Korean insulation standards and passive house. To evaluate building energy performance, the building airtightness values of two stages was ACH50 = <TEX>$3.0h^{-1}$</TEX> for common domestic timber house constructed recently, and ACH50 = <TEX>$0.6h^{-1}$</TEX> for passive house. Consequently, four cases of the building energy performance according to the combination of U-value with airtightness were evaluated. The test house for evaluation was located in Seoul and its energy performance was evaluated with CE3 commercial building energy simulation program. The result showed that enhanced insulation from level I to II reduced <TEX>$14kWh/(m^2{\cdot}a)$</TEX> of annual heating energy demand regardless of airtightness.

Dynamic modelling of multidimensional thermal bridges in building envelopes: Review of existing methods, application and new mixed method

This study presents four approaches to model correctly the heat transfer through a thermal bridge and simply introduce it into building energy simulation programs. These approaches are based on the equivalent wall method: defining a 1-D three-layer wall, replacing the thermal bridge, which has the same steady and dynamic thermal behaviours as the thermal bridge. The four methods are tested on 1-D simple cases. However, the best approach is a fifth method, a mix between the principles of the structure factors method and a harmonic method: it leads to very accurate results and a unique solution. This mixed method is tested on a 2-D thermal bridge, junction between floor and exterior wall, and the results are again accurate and much better than a classic consideration of the thermal bridge.

Radiometric Boundary Condition Models for Building Performance Simulation: An Empirical Assessment

Designand operation of buildings in view of optimal thermal and visual performance can benefit from deployment of appropriate simulation tools. Specifically, the design and configuration of building-integrated renewable energy systems (solar-thermal collectors and photovoltaic panels) can be effectively supported via reliable computation of incident solar radiation. Toward this end, advanced building energy and lighting simulation programs typically use high-resolution sky models. In this contest, the present contribution addresses the reliability of these models based on long-term high-resolution data collected at the observatory of the Department of Building Physics and Building Ecology at the Vienna University of Technology, Austria. This observatory is equipped with radiometric and photometric sensors to measure global and diffuses horizontal irradiance and illuminance, global vertical irradiance and illuminance of the four cardinal orientations, as well as sky radiance and luminance values for discrete sky patches. To evaluate the performance of two widely used sky models, we compared simulated and measured vertical irradiance values as well as patch radiance values. The statistical appraisal of the comparison points to limits in the predictive accuracy of both models.

Origins of analysis methods used to design high-performance commercial buildings: Whole-building energy simulation

Many commercial buildings today do not perform the way they were simulated. One potential reason for this discrepancy is that designers using building energy simulation programs do not fully understand the analysis methods that the programs are based on and may therefore have unreasonable expectations about the actual system performance or energy use. Therefore, the purpose of this study is to trace the origins of the most widely used building energy simulation programs and the analysis methods of thermal envelope loads used in the software to analyze high-performance commercial buildings in the United States. Such an analysis is important to better understand the capabilities of building energy simulation programs so they can be used more accurately to simulate the performance of an intended design. In this study, a new comprehensive genealogy chart was developed to support the explanations for the origins of the analysis methods of thermal envelope loads used in whole-building energy simulation programs. Two other works (Oh and Haberl 2015a, 2015b) explained the origins of the analysis methods of solar photovoltaic, solar thermal, passive solar, and daylighting simulation programs.

THE ENERGY SAVINGS POTENTIAL OF OPTIMIZED SLAB-ON-GRADE FOUNDATION INSULATION RETROFITS

A recently developed 3-dimensional earth contact simulation program that operates as a subroutine of the EnergyPlus whole building energy simulation program was used to evaluate the energy performance and cost-effectiveness of retrofit slab-on-grade (SOG) foundation insulation. An optimized retrofit insulation design utilizing hydro-vacuum excavation was developed that generated 8.4 % larger metered (or site) energy savings at a $428 lower cost than the IECC 2012 requirement in a Minneapolis, MN climate for a 400 ft2 test building. The energy performance and cost effectiveness of single and multi-family buildings was assessed for climate Zones 4 – 7. With reference to the Building America B10 benchmark, the highest site energy savings of 5 % was realized for a single family home in Duluth, MN, and the lowest savings of 1.4 % for a 4-unit townhouse in Richmond, VA. SOG foundation insulation retrofit simple paybacks ranged from 18 to 47 years. Thus it is likely that larger energy savings of 10% or more with concomitantly reduced simple paybacks can only be realized in well-insulated buildings.

Multi-level optimization of building design, energy system sizing and operation

Multi-level optimisation divides a problem into sections such that each can be addressed using the most appropriate evaluation and optimisation processes. A methodology is proposed to address the design and operation of a building and its energy system, split into three levels: building design, system design and system operation. The optimisation techniques used are a multi-objective genetic algorithm (design) and mixed-integer linear programming (operation); the evaluation methods used are the building energy simulation program EnergyPlus (building level) and the ‘energy hub’ model (system level). The objective functions used here were annual carbon emissions and initial capital cost (for the multi-objective design problem) and annual running costs (for the single objective operational problem).The methods used are described in detail, and the proposed methodology is applied to a case study concerning an office building. The detailed results presented include the trade-off front of optimal design-level solutions, the convergence of the optimisation, trends in the associated design variable values, derived properties of each solution, the operational variable values, and the run-times of the operational optimisation. Conclusions are drawn regarding the case study and the overall approach, and future directions are suggested.

Dynamic effect of thermal bridges on the energy performance of a low-rise residential building

The existence of thermal bridges in building envelopes affects the energy performance of buildings, their durability and occupants’ thermal comfort. Typically the effect of thermal bridges on the energy performance is taken into account by implementing an equivalent U-value in 1D whole building energy simulation program. This treatment accounts for the effect of thermal bridges on the overall thermal transmittance, while their thermal inertia effect is ignored. The presence of thermal bridges not only reduces the overall thermal resistance but also changes the dynamic thermal characteristics of the envelope.This paper investigates the dynamic effect of thermal bridges on the energy performance of residential buildings through simulations. A two-story residential building is used as a case study. Three methods, namely equivalent U-value method, equivalent wall method, and direct 2D/3D modeling method, are implemented in WUFI Plus, a whole building Heat, Air and Moisture (HAM) modeling program. Simulations are carried out for two climates with different insulation levels. Simulation results show that for the cold climate the annual heating load of this building with the inclusion of thermal bridges modeled using 3D dynamic method is 8–13% higher than that modeled using the equivalent U-value method, and 4–9% higher than that modeled using the equivalent wall method. With the increase of the insulation level, the percentage effect of thermal bridges on the heating load increases, while the difference among the three methods decreases. For the hot climate, simulation results show that the presence of thermal bridges increases the annual cooling load by 20%. Compared to the 3D dynamic method, the annual cooling load is underestimated by 17% using the equivalent U-value method and by 14% using the equivalent wall method, respectively.

소규모 사무공간에서의 건물 외피 성능에 따른 EnergyPlus와 eQuest 시뮬레이션 결과 비교에 관한 연구

The purpose of this study is to compare two building energy simulation programs'(EnergyPlus and eQuest) heating/cooling load, and to find the differences by analyzing algorithm, input method and default input parameters based on the ASHRAE Standard 140-Case600. EnergyPlus calculates the inside surface temperatures by solving the heat balance, but eQuest assumes that the inside surface temperature of a thermal zone is equal to the zone air temperature. This result in zone air temperature difference(<TEX>$1.16^{\circ}C$</TEX> average) is due to occurred load differences. Change of U-value of vertical surface causes as 7~8 % of the heating load difference and 25~26 % of the cooling load difference. The result of changed SHGC is similar. But the result from infiltration shows a little different tendency(The heating load differences decrease from 7 % to -16 % and cooling load differences increase from -26 % to -19 %). All of these differences are caused by algorithm discrepancies of convection coefficients, actual air change rate and solar transmittance.

Development of a home energy audit methodology for determining energy-efficient, cost-effective measures in existing single-family houses using an easy-to-use simulation

This study developed a home energy audit methodology for determining energy-efficient, cost-effective measures in existing single-family houses using an easy-to-use simulation. The overall goal of this study was to provide an easy-to-use, time-saving home energy audit for users who are not familiar with building physics and building energy simulation programs such as homeowners, etc. The methodology that was developed can identify the cause of over-consumption in a house prior to a walk-through investigation by showing where the energy is inefficiently being used when compared to houses of similar sizes in similar climates. In order to accomplish this, a methodology for an easy-to-use, calibrated simulation that can determine potential energy conservation measures for existing single-family houses was developed. In addition, to verify the methodology, the results were compared to those obtained from a detailed, as-built residential energy simulation to determine if both the simulation results identified the same potential energy conservation measures. As a result, it was found that the easy-to-use simulation can be used as an as-built simulation for a home energy audit procedure with acceptable results for the case-study house.

Influence of plant coverage on the total green roof energy balance and building energy consumption

This study quantifies the influence of green roof plant coverage on the building energy consumption and the substrate energy balance components. The analysis started with the implementation of a green roof model that accounts for the effects of plant coverage into the U.S. Department of Energy (DOE) building energy simulation program, EnergyPlus. Using the DOE reference building models, thirty different cases were simulated considering different green roof plant coverage, building type, and building age for two different climates. The results indicated that the green roof substrate surface temperature decreases with increasing plant coverage. This temperature decrease is primarily due to the decrease in the amount of absorbed solar radiation on the substrate surface and also an increase in the substrate surface evaporation. For the base-case simulation, due to the plant shading effects, the total daily received radiation at the bare-soil surface is 32% (6.2kWhm−2) higher than that at the fully-covered green roof substrate surface. Furthermore, the annual cooling (heating) load decreases (increases) with the rate of 13 (0.88)kWhm−2 of plant coverage area. The aim of this study is to show the importance of considering plant coverage in green roof simulations and building energy demand predictions.

Assessment of the Potential to Achieve very Low Energy Use in Public Buildings in China with Advanced Window and Shading Systems

As rapid growth in the construction industry continues to occur in China, the increased demand for a higher standard living is driving significant growth in energy use and demand across the country. Building codes and standards have been implemented to head off this trend, tightening prescriptive requirements for fenestration component measures using methods similar to the U.S. model energy code American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 90.1. The objective of this study is to (a) provide an overview of applicable code requirements and current efforts within China to enable characterization and comparison of window and shading products, and (b) quantify the load reduction and energy savings potential of several key advanced window and shading systems, given the divergent views on how space conditioning requirements will be met in the future. System-level heating and cooling loads and energy use performance were evaluated for a code-compliant large office building using the EnergyPlus building energy simulation program. Commercially-available, highly-insulating, low-emittance windows were found to produce 24%–66% lower perimeter zone HVAC electricity use compared to the mandated energy-efficiency standard in force (GB 50189-2005) in cold climates like Beijing. Low-e windows with operable exterior shading produced up to 30%–80% reductions in perimeter zone HVAC electricity use in Beijing and 18%–38% reductions in Shanghai compared to the standard. The economic context of China is unique since the cost of labor and materials for the building industry is so low. Broad deployment of these commercially available technologies with the proper supporting infrastructure for design, specification, and verification in the field would enable significant reductions in energy use and greenhouse gas emissions in the near term.

Experimental and theoretical study on the effect of window films on building energy consumption

Solar control films are designed to absorb or reflect the incident solar radiation, in order to reduce solar transmission through window glass. In the present study, the glass surface temperatures were measured for selected solar window films on various applications, and compared to the cases of the same window glass types without solar window films. Dynamic simulation models are also developed with the aid of the building energy simulation program EnergyPlus. After experimental validations, the computer models are used to evaluate the energy saving potentials of the subject samples of solar window films as applied onto glazing of three different function rooms in Hong Kong, namely office, shopping mall and hotel guest room. The results show that the thermal performance of the film applications on clear glass is better than on tinted or laminated glass windows. Solar films have very good energy saving potential when applied to all three functional areas in commercial buildings, and the best results are found in office applications.

Optimized Building Automation and Control for The Improvement of Energy Efficiency and Climate Comfort Of Office Buildings

The object of the examination is a typical office building of the 1990s, owned by a multinational company -Siemens- dedicated to energy awareness. The building also meets the energy efficiency category ‘A’ under the 7/2006 TNM Hungarian regulations concerning the energy performance definition of buildings. However, demand has emerged to implement additional changes to reduce energy usage whilst keeping the current climate comfort or even improving it. International experience forecasts around 30% energy saving potential due to optimization of the building automation and energy management system, and thus the interaction and collaboration between the building geometry, structures and services systems. The project has been built in the IDA ICE complex building energy simulation program. Running a one-year dynamic simulation will provide data that can be compared with the measured data of the actual building, so the model can be adjusted and validated to real data. After the calibration it is now possible to test the ideas under safe conditions, in a virtual surrounding. Once a particular vision of the model is proven to work effectively, it is possible to apply this to the real building control management as well.

Optimized building automation and control for the improvement of energy efficiency and climate comfort of office buildings

The object of the examination is a typical office building of the 1990s, owned by a multinational company -Siemens- dedicated to energy awareness. The building also meets the energy efficiency category ‘A’ under the 7/2006 TNM Hungarian regulations concerning the energy performance definition of buildings. However, demand has emerged to implement additional changes to reduce energy usage whilst keeping the current climate comfort or even improving it. International experience forecasts around 30% energy saving potential due to optimization of the building automation and energy management system, and thus the interaction and collaboration between the building geometry, structures and services systems. The project has been built in the IDA ICE complex building energy simulation program. Running a one-year dynamic simulation will provide data that can be compared with the measured data of the actual building, so the model can be adjusted and validated to real data. After the calibration it is now possible to test the ideas under safe conditions, in a virtual surrounding. Once a particular vision of the model is proven to work effectively, it is possible to apply this to the real building control management as well.

A STRATEGY FOR ENERGY PERFORMANCE ANALYSIS AT THE EARLY DESIGN STAGE: PREDICTED VS. ACTUAL BUILDING ENERGY PERFORMANCE

Developments in information technology are providing methods to improve current design practices, where uncertainties about various design elements can be simulated and studied from the design inception. Energy and thermal simulations, improved design representations and enhanced collaboration using digital media are increasingly being used. With the expanding interest in energy-efficient building design, whole building energy simulation programs are increasingly employed in the design process to help architects and engineers determine which design strategies save energy and improve building performance. The purpose of this research was to investigate the potential of these programs to perform whole building energy analysis during the early stages of architectural design, and compare the results with the actual building energy performance. The research was conducted by simulating energy usage of a fully functional research laboratory building using two different simulation tools that are aimed for early schematic design. The results were compared with utility data of the building to identify the degree of closeness with which simulation results match the actual energy usage of the building. Results indicate that modeled energy data from one of the software programs was significantly higher than the measured, actual energy usage data, while the results from the second application were comparable, but did not correctly predict monthly energy loads for the building. This suggests that significant deviations may exist between modeled and actual energy consumption for buildings, and more importantly between different simulation software programs. Understanding the limitations and suitability of specific simulation programs is crucial for successful integration of performance simulations with the design process.

Evaluation of Different Thermal Models in EnergyPlus for Calculating Moisture Effects on Building Energy Consumption in Different Climate Conditions

The calculation of building energy consumption is needed in all architecture design projects. Building simulation software is used to predict the indoor air temperature and relative humidity as well as the building's heat loads. The calculation of accurate heat load requires calculating coupled heat and moisture transfer in building envelopes and the hygrothermal interactions between the envelopes and the environment. However, the moisture effects of building envelopes are often neglected. This would bring much inaccuracy to the simulation results. Based on different calculation methods, many numerical building energy simulation programs have been developed. This paper evaluates the accuracy and the applicability of three thermal models in EnergyPlus (CTF-Conduction Transfer Function model, HAMT-Combined Heat and Moisture Transfer model, EMPD-Effective Moisture Penetration Depth model) for calculating moisture effects on building energy consumption in different climate conditions. The effects of different room infiltration rate on the accuracy of different models are also analyzed.

Transferring the south solar energy to the north facade through embedded water pipes

In the cold sunny winter days, when the south wall is well insulated, a significant amount of solar energy falling on this facade is not transferred to the inside. In this study, a novel closed wall-loop system is proposed to capture this wasted energy available during non-cloudy winter days and transfer it to the cooler north facade through water pipes embedded in an exterior aerogel-based insulating coating. The coating's projection technique through spraying or plastering allows the easy implementation of this system. We present the proposed system with all the mathematical equations and numerical model. This model is then validated against experimental data found in the literature. To test its performance on a full-scale house, this MATLAB numerical model is coupled to the whole building energy simulation program EnergyPlus through co-simulation. Results show that the reductions in the annual heating load for the house adopting this system relative to the one without it are between 28 and 43% for new houses and 15–20% for old houses for Mediterranean climate. For other climates, the reductions vary between 6% and 26%. The heat losses through the north facade are reduced by about 60–88% in the Mediterranean climate and about 20–50% in the other climates.

Building Performance Analysis and Simulation: We’ve Come a Long Way

Back in 1981, when I started doing building energy performance simulation for pre-design and energy efficiency retrofit work, building simulation was in its infancy. There were only a handful of building energy simulation programs, with DOE-2, ESP-II, BLAST, TRACE and MERIWHETHER being the most commonly used ones by consultants [1]. These programs required "mainframe" computers, so I used to prepare the input files on a Radio Shack TRS-80, send it over a telephone modem to a company in Toronto that ran the simulation on a mainframe computer overnight and shipped the printed output to me by courier in the morning. Each run had a turn-around time of almost 48 h, and the run-time and courier charges were about $100, almost as much as a day's salary for a young engineer. [...]