Building Energy Requirements Research Articles

A Comparative Study of Energy Consumption for Residential HVAC Systems Using EnergyPlus

Energy conservation and sustainability have become an attractive field for research due to the growth in population and continuing search for better living standards. Heating, Ventilation, and Air Conditioning (HVAC) systems account for almost half of consumed energy in buildings and around 10 to 20% of total energy consumption in developed countries. In general, the trend of installing central HVAC systems increases in residential and commercial buildings. In this research, a study of energy consumption of HVAC systems in residential buildings has been conducted with the aim to compare those systems from an energy consumption point of view. The final goal of this research is to reduce energy requirements of residential buildings sector to save energy and reduce carbon emission. A medium size residential building in the city of Tripoli, Libya, was selected as a case study. EnergyPlus building simulation software along with OpenStudio software were used to model the house and HVAC systems. The results show that the virtual component “ideal air loads” used in EnergyPlus is very easy to use, however, its calculated energy consumption is overestimated compared to other models. Therefore, using that component can be misleading and may result in high monthly and annually energy consumption results. The results also show that in a residential building, unitary systems consume the least annual energy consumption compared to other models. It was concluded that variations in energy consumption of the considered HVAC systems decrease as the coefficient of performance (COP) increases and visa verse.

The Possibilities of Modification of Crop-based Insulation Materials Applicable in Civil Engineering in Low-energy and Passive Houses

Currently in Europe there is a growing trend towards low energy and passive houses where natural materials are often used. These materials are very promising in terms of environmental protection. The use of green thermal insulation materials brings a significant reduction of energy requirements of buildings which is their major benefit. Previous research shows that crop-based thermal insulating materials exhibit very good thermal insulation and acoustic properties. However, their structure is different from conventional insulation materials (EPS, XPS, PUR, and MW) and their hygrothermal behaviour is much different. This article focuses on studying the behaviour of fibrous green insulations under humidity and moisture load. The test samples of the materials were treated with different types of hydrophobic agents before testing. The goal of the experiments was to reduce the sensitivity of the insulation to humidity and moisture (i.e. reduce their hygroscopicity). The chemical treatment of the fibres should improve the practical properties of the thermal insulation materials and extend their service life after they have been incorporated in a structure and attacked by moisture.

A Solar Heating and Cooling System in a Nearly Zero-Energy Building: A Case Study in China

The building sector accounts for more than 40% of the global energy consumption. This consumption may be lowered by reducing building energy requirements and using renewable energy in building energy supply systems. Therefore, a nearly zero-energy building, incorporating a solar heating and cooling system, was designed and built in Beijing, China. The system included a 35.17 kW cooling (10-RT) absorption chiller, an evacuated tube solar collector with an aperture area of 320.6 m2, two hot-water storage tanks (with capacities of 10 m3 and 30 m3, respectively), two cold-water storage tanks (both with a capacity of 10 m3), and a 281 kW cooling tower. Heat pump systems were used as a backup. At a value of 25.2%, the obtained solar fraction associated with the cooling load was close to the design target of 30%. In addition, the daily solar collector efficiency and the chiller coefficient of performance (COP) varied from 0.327 to 0.507 and 0.49 to 0.70, respectively.

Impact of coupled heat and moisture transfer effects on buildings energy consuption

Coupled heat, air, and moisture transfers through building envelope have an important effect on prediction of building energy requirements. Several works were conducted in order to integrate hygrothermal transfers in dynamic buildings simulations codes. However, the incorporation of multidirectional hygrothermal transfer analysis in the envelope into building simulation tools is rarely considered. In this work, coupled heat, air, and moisture (HAM) transfer model in multilayer walls was established. Thereafter, the HAM model is coupled dynamically to a building behavior code (BES).The coupling concerns a co-simulation between COMSOL Multiphysics and TRNSYS software. Afterward, the HAM-BES co-simulation accuracy was verified. Then, HAM-BES co-simulation platform was applied to a case study with various types of climates (temperate, hot and humid, cold and humid). Three simulations cases were carried out. The first simulation case consists of the TRNSYS model without HAM transfer model. The second simulation case, 1-D HAM model for the envelope was integrated in TRNSYS code. For the third one, 1-D HAM model for the wall and 2-D HAM model for thermal bridges were coupled to the thermal building model of TRNSYS. Analysis of the results confirms the significant impact of 2-D envelope hygrothermal transfers on the indoor thermal and moisture behavior of building as well as on the energy building assessment. These conclusions are shown for different studied climates.

Modelling relationship among energy demand, climate and office building features: A cluster analysis at European level

More than one-third of the energy demand of industrialised countries is due to achieving acceptable conditions of thermal comfort and lighting in buildings. Energy demand in buildings depends on a combination of several parameters, such as climate, envelope typologies, occupant behaviour, and intended use. Indeed, assessing a building’s energy performance requires substantial input data describing constructions, environmental conditions, envelope thermo-physical properties, geometry, control strategies, and several other parameters. This has been a very active area of research in recent years, and several numerical approaches have been developed for building simulation; furthermore, most of these approaches have been tested and implemented in specialised software tools. However, the use of these tools poses many challenges in regards to the retrieval of reliable and detailed information, setting a steep learning curve for engineers and energy managers. It is often more convenient to have a simplified model that allows the evaluation of energy demand with a good level of accuracy and without excessive computational costs or user expertise. In this work, the authors extrapolate a set of simple correlations to permit a fast preliminary assessment of heating energy demand for office buildings. Data employed to build the correlations come from detailed dynamic simulations performed in TRNSYS environment. The models were built according to the standards and laws of building energy requirements in seven different European countries. For a more general assessment, the authors identified three cities for each country; for each location, three models with different shape factors were considered (S/V=0.24, 0.5 and 0.9). The results obtained from the simulations allowed for the determination of direct correlations among the thermal energy demand for space heating HDD and S/V values. In this way, the authors provided simple equations for a reliable and easy-to-use preliminary assessment of the energy demand of non-residential buildings to planners and designers, taking into account regulation dictated by law in each considered country.

Prefabricated Wood Elements for Sustainable Renovation of Residential Building Façades

Prefabricated elements to provide environmentally friendly, energy- and cost-efficient solutions for the building envelope have been studied. The newly developed element system has a high level of flexibility since it is possible to adjust the length of the connection rods according to the building's energy requirements and it can be mounted on timber, concrete and brick structures. Adjustability to different types of buildings structures, materials, tolerances, geometries and energy requirements makes it very applicable and efficient.

Understanding the Emergence of Policies – Revising Building Regulations in Light of the Three Pillars of Sustainability

The building regulations for the Norwegian construction industry (TEK10) undergo a major revision in 2015. This case study firstly examines to what degree social and economic consequences are taken in consideration when deciding energy (environmental) requirements in buildings. Secondly, it looks at the analysis and assessments that lay the basis for the decision of new requirements. The economic and social consequences of new building requirements are significant. These are, however, found to be to a smaller degree taken in consideration than the environmental perspective. Higher requirements to energy use in buildings are expected to drive the housing market up.

The impact of natural ventilation on building energy requirement at inter-building scale

Inter-building effect is responsible for affecting buildings’ primary energy requirement for heating, cooling, and lighting. Nevertheless, the impact of natural ventilation should also be considered while predicting building energy demand, since it is documented to substantially affect indoor environmental quality and thermal comfort. This paper investigates the impact of natural ventilation on building primary energy requirement prediction. The Inter-Building Effect (IBE) approach is applied in a typical residential block in Italy. A sensitivity analysis is performed to determine the key input parameter among (i) climate boundary, (ii) infiltration rate, (iii) opening percentage, and (iv) wind strength. Two scenarios, i.e. the stand-alone building and the same building surrounded by its neighborhood, are compared. The thermal-energy dynamic simulation of the different scenarios is carried out to investigate the impact of outdoor airflows on building primary energy requirement for heating and cooling and on indoor thermal comfort, investigated by means of the Thermal Deviation Index method. Inaccuracies in energy need prediction imputable to natural ventilation without taking into account the IBE are detected. The findings show that IBE is much more affected by buildings’ opening percentage, infiltration rate, and local wind compared to the weather context since IBE is a local microscale phenomenon.

Proposal for optimum combination of reflectivity and insulation thickness of building exterior walls for annual thermal load in Japan

This paper is a proposal to optimize the combination of surface reflectivity and the insulation thickness of exterior walls for energy savings in regions of Japan. Calculations of building thermal loads and economic analysis of the total cost for six cities from high-latitude to low-latitude regions of Japan were carried out for a range of surface reflectivity and insulation thickness of exterior walls. The results can be used in design to decrease the energy requirements of buildings. We estimated the annual thermal loads of a simulated building floor and analyzed the cost of the building envelope in Sapporo, Tokyo, Nagoya, Osaka, Fukuoka and Naha, Japan, varying the surface reflectivity of the exterior walls from 0.1 to 0.8, and insulation thickness of the exterior walls from 10 mm to 100 mm, using the thermal load calculation software, New HASP/ACLD-β and cost analysis. Optimum combinations of surface reflectivity and insulation thickness for each region are proposed.

Saving energy is not easy: An impact assessment of Dutch policy to reduce the energy requirements of buildings

The Dutch Government stimulates the application of energy efficiency measures to reduce the energy requirements of buildings, which are responsible for about 20% of the Dutch CO2 emissions. For our assessment, we followed a qualitative approach, due to a lack of data. We reviewed the mix of policy instruments and used stakeholder surveys and interviews. We found that energy use is not very likely to decline fast enough to achieve the Dutch policy targets for 2020. For new buildings, the policy mix works well, but its contribution to the policy targets is limited. For non-residential buildings the current Act, which obliges enterprises to take cost-effective measures, could be enforced to a greater degree. For privately owned homes a more compelling policy is needed. An alternative policy option would be to make taxation dependent on the energy label of residential houses. This would stimulate residents to take action while retaining the desired autonomy. For rental housing, binding agreements between municipalities and housing corporations may lead to more energy saving measures. Finally, we conclude that the Dutch energy tax is an important pillar of the current policy. It provides higher cost-effectiveness of energy saving measures and legitimates more strict energy efficiency standards.

Effects of Inhomogeneities on Heat and Mass Transport Phenomena in Thermal Bridges

The interest of calculating the effects of thermal bridges in buildings energy consumption is growing, due to recent energy saving regulations applied in different countries. The widespread use of insulating materials to reduce energy requirements of buildings, often employed for intermediate insulation of the building envelope, makes thermal bridges a crucial point in the energy analysis of building envelopes. Furthermore, heat losses through thermal bridges often lead to building pathologies due to moisture condensation. Therefore, thermal bridges need to be correctly characterized in the building design stage in order to reduce heat losses and avoid materials degradation. The authors numerically simulate, by using finite elements, the steady-state and dynamic three-dimensional (3D) heat and vapor transport in inhomogeneous thermal bridges and building envelopes. The aim of the present work is to show the importance of taking into account the presence of inhomogeneities (i.e., metal stud) in building materials for the calculation of actual heat losses and water condensation in 3D thermal bridges. The obtained heat transfer results are verified against the reference data of the technical standard UNI EN ISO 10211. The proposed microscopic approach is essential to calculate the actual heat losses of three-dimensional thermal bridges and building envelopes and to overcome condensation problems.

Estimating building energy consumption using extreme learning machine method

The current energy requirements of buildings comprise a large percentage of the total energy consumed around the world. The demand of energy, as well as the construction materials used in buildings, are becoming increasingly problematic for the earth's sustainable future, and thus have led to alarming concern. The energy efficiency of buildings can be improved, and in order to do so, their operational energy usage should be estimated early in the design phase, so that buildings are as sustainable as possible. An early energy estimate can greatly help architects and engineers create sustainable structures. This study proposes a novel method to estimate building energy consumption based on the ELM (Extreme Learning Machine) method. This method is applied to building material thicknesses and their thermal insulation capability (K-value). For this purpose up to 180 simulations are carried out for different material thicknesses and insulation properties, using the EnergyPlus software application. The estimation and prediction obtained by the ELM model are compared with GP (genetic programming) and ANNs (artificial neural network) models for accuracy. The simulation results indicate that an improvement in predictive accuracy is achievable with the ELM approach in comparison with GP and ANN.

Energy and Cost Analyses of Solar Photovoltaic (PV) Microgeneration Systems for Different Climate Zones of Turkey

The environmental and energy problems that have arisen in Turkey because of the dramatically increase in energy consumption require the implementation of energy efficiency and microgeneration measures in the building sector which is the main sector of primary energy consumption. Since Turkey is highly dependent on exported energy resources, the basic energy policy approach is based on providing the supply security. In this regard, supporting for in situ energy production, encouraging the use of renewable energy sources and the systems such as microgeneration systems in order to meet the energy requirements of buildings would be considered as a key measure for resolving the energy related challenges of Turkey and dealing with the sustainability issues. Turkey’s geographical location has several advantages for extensive use of most of the renewable energy sources such as especially solar energy. However, this huge solar energy potential is not being used sufficiently in residential building sector which is responsible for the great energy consumption of Turkey. Therefore, this paper aims to introduce a study which investigates, on a life cycle basis, the environmental and the economic sustainability of solar Photovoltaic (PV) microgenerators to promote the implementation of this system as an option for the renovation of existing residential buildings in Turkey. In this study, main parameters which were related to the distribution of modules to be installed in flat roofs and facades and the evaluation of the PV systems were taken into account. The effect of these parameters on energy generation of PV systems was analyzed in a case study considering different climate zones of Turkey; and the decrease in the existing energy consumption of the reference building was calculated.

Dynamic Thermal-energy Performance Analysis of a Prototype Building with Integrated Phase Change Materials

The use of PCMs for improving buildings’ thermal comfort conditions and reducing summer cooling need has been largely investigated in the last decade. The capability of these materials of storing heat in latent form has been pointed out, especially when integrated in building envelopes. This paper deals with the analysis of the benefits in terms of buildings’ energy saving generated by the integration of PCMs inside two types of membrane for roofing applications, i.e. a traditional bitumen membrane and an innovative cool polyurethane-based membrane. To this aim, the dynamic simulation of the energy performance of a test-room was carried out. Four configurations were simulated and compared: (i) roof covered by a bitumen sheet membrane, (ii) roof covered by a cool membrane, (iii) the cool membrane with integrated PCMs, and (iv) the bitumen membrane with integrated PCMs. Both winter and summer conditions were studied. The results showed that PCMs integrated into the cool membrane are able to guarantee a 10.4% cooling energy saving, while PCMs integrated into the bitumen membrane generate a 12.6% of energy reduction for cooling if compared to the only bitumen membrane. The same roof configurations without taking into account the roof insulation layer generate a reduction of the cooling energy requirement of about 9.4% and 16.6%, respectively. In winter conditions, the reduction of the heating demand generated by the integration of PCMs inside the bitumen membrane is about 4.4% and 6.9%, with and without considering the roof insulation, respectively. Additionally, the heating energy saving generated by including PCMs into the cool membrane is equal to 5.4% and 8.4%, with and without considering the roof insulation layer, respectively. These results demonstrated that the integration of PCMs in both cool and non-cool roof membranes is able to reduce building energy requirement in both summer and winter conditions, especially in non-insulated roof configuration.

Annual heating energy requirements of office buildings in a European climate

The concept of implementing energy savings to reduce greenhouse gas emissions has become a key element of energy policies of any industrialized country. In the civil sector and specifically, energy savings for office buildings, there are still opportunities for further enhancements related to correctly determining the air conditioning thermal requirements. However, there is a lack of simple correlations that allow a preliminary assessment for a single building or correlations that can be quickly applied at the district level. This paper proposes several simple correlations that determine the heating loads of a typical office building by only knowing the Degree-Days of a specific European location. The authors have developed a dynamic model of an office building, considering the different energy regulations in force in several European countries such that the building model is as energy-efficient as possible in each examined location. Furthermore, the standard requirements related to the employment rate, indoor ventilation and indoor gain have been included. The results from several simulations performed in the TRNSYS environment have enabled the development of mathematical relationships valid for seven European countries and three continental zones (northern, central and southern) with notably high correlation coefficients. The proposed equations can be useful for determining the heating load of non-residential buildings with an appropriate level of detail for a rough energy plan at the district level.

The suitability of high resolution downscaled seasonal models for the energy assessment of the building sector

The present work attempts to provide more accurate estimate of HDD and CDD and investigates the suitability of high resolution downscaled seasonal climatic forecasting models for assessing and accurately estimating the energy demands of buildings. The analysis has been established through a series of indices for estimating heating (HDD) and cooling degree days (CDD) using interpolated hourly data which were produced from the model output. The work has considerable potential to provide refined inputs for assessing building sector-specific vulnerability to climate change: energy supply and demand.In this work the application of the above mentioned methodological approach in the assessment of the energy performance and requirements of buildings on Greece are presented, for a period and with a forecast horizon of 6 months. The ARW-WRF model has been set up and validated to produce downscaled climatological fields for Greece, forced by the output of the CFSv2 model, with a horizontal spatial resolution of 5km×5km. The data, that covered all Greek regions and climatology zones according to the existing building regulations code and the region elevation present a very reasonable correlation with data published in previous studies.

An analytical model for the evaluation of the correction factor FW of solar gains through glazed surfaces defined in EN ISO 13790

EN ISO 13790 is the international standard used for the calculation of the thermal energy requirement of buildings. The evaluation of solar gains through the glazed surfaces is done with a simplified procedure that determines the transmitted solar energy through the transparent surfaces as the product of the normal incidence solar gain coefficient ggl,n and a correction factor FW, that considers the directional aspects of the beam solar radiation. In the absence of adequate national guidelines, the correction coefficient FW in EN ISO 13790 for non-scattering glazing is set constant and equal to 0.90. In this paper, the results obtained by the TRNSYS computer code demonstrate that a generalized use of a constant value of FW=0.90 provides significant deviations. Therefore, a correlation to evaluate a variable FW coefficient, in function of the incidence angle of solar radiation and of the number of glass panes, is reported. The accuracy of the obtained results was verified comparing the calculated values with those provided by the TRNSYS software. Finally, with reference to two buildings located in two localities with different weather data, the thermal energy needs by applying the EN ISO 13790 procedure with FW=0.90 and with variable FW have been compared.

Influence of Shading and Transparent Surfaces on Historical Building Energy Retrofit

This study aims to assess the influence of greenery shading and transparent surfaces on historical building’s energy demand under a retrofit point of view. To achieve this goal, the energy requirement of the whole building has been considered. In order to improve buildings energy efficiency several simulations have been performed. In particular, the effects of some interventions related to different windowed elements, characterized by progressively improved thermal properties, have been taken into account.

Comparison between different measures to reduce cooling requirements of residential building in cooling-dominated environment

In hot climate region like Arabian Peninsula, air conditioning systems are the major energy consumer. Therefore, there are compelling reasons to study the energy requirements in buildings sector to reduce the energy requirements and its environmental impact.Current paper shows the impact of different improvements on reducing cooling load of buildings in hot climate. The examined factors are (1) total heat transfer coefficient of the external shell, (2) indoor temperature, (3) lighting efficacy. For this purpose, a common type of residential house in Qatar was chosen as a case study. The cooling load was estimated using simulation model. The simulations show that there is big potential to reduce the cooling requirements in Qatar up to 46%. A brief economic comparison between the examined factors was done. The economic analysis shows that the payback time of applying the examined factors fall between 0.5 and 2 years.

Performance of photovoltaics in non-optimal orientations: An experimental study

Buildings are one of the biggest energy consumers in our world. The concept of zero energy building (ZEB) is an attractive approach in order to reduce the energy requirement of buildings leading to more sustainable cities. Building integrated photovoltaics (BIPV) is one suitable technology for providing electricity to the buildings with a minimum impact. Traditionally, photovoltaics (PV) have been installed looking for maximum yearly energy production.In this work the feasibility of PV working in non-optimal orientations will be explored by using two experimental setups: a photovoltaic façade with a southwest orientation and an architectural model of a building with the façades in the cardinal points, covered with PV. The results show interesting features, considering yearly and hourly generation profiles. Although the annual energy production for the façades and the roof is between 50% and 76% of an optimum angle installation, the façades have a more stable production along the year: monthly production can vary by a factor 2 vs a variation of factor 4 for irradiance. Moreover, the hourly production profiles are displaced from noon so they can match the demand. With some current net metering proposals, non-optimal orientations could even be more economical than the maximum producing orientation.