Extensive Comparative Analysis Of Two Building Energy Simulation Codes For Southern Europe Climates: Heating And Cooling Energy Needs and Peak Loads Calculation In TRNSYS And EnergyPlus

In order to evaluate the energy performance of buildings, both in heating and in cooling periods, the simulation codes can be used. Moreover, in accordance with the technical Standard EN ISO 13790:2008, the simulation codes can be employed for refining the steady-state methods, and particularly the utilization factors estimations, in accordance with the procedure proposed. As the various simulation codes implement different capabilities and refer to different mathematical models and calculation assumptions, the necessary validation steps which are used for diagnostic purposes are not enough to ensure the agreement of the results over a wider range of configurations and conditions. The main dynamic simulation codes have been generally evaluated according to the Standard ANSI/ASHRAE 140:2007 (BESTEST). By this approach the user can choose a software among those successfully tested, giving acceptable deviations between the computed output and the reference values for a selected number of reference buildings defined in the Standard. However the number of those reference building configurations is limited and the considered features are not representative of the common building stock present for instance in Southern Europe. Moreover, as those configurations were selected for diagnostic purposes, they are expected to produce unacceptable biasing when considered with statistical approaches in order to improve the quasi steady state approaches as the one proposed in the technical standard EN ISO 13790:2008. In this work a procedure to identify the main causes of deviation has been developed and has been applied to two well-known dynamic simulation software: TRNSYS (version 16.1) and EnergyPlus (version 7). The approach is based on a factorial plan of comparison aimed to investigate the main variables related to the envelope of the building and its behavior: variations in geometry and boundary conditions (dimensions and orientation of the glazing, amount of dispersing surface) envelope characteristics (walls insulation and heat capacity, insulation and solar transmittance of glazings) internal gains. From the combination of the values of the above variables, more than 1600 different configurations have been obtained for two Italian climatic conditions, each of which providing monthly values for heating and cooling needs and for heating and cooling peak loads. Thanks to the large number of configurations, the monthly heating and cooling energy needs and peak loads have been analysed with inferential statistics, which allowed to evaluate the agreement between the outputs and to characterize the weight of the different variables in causing the deviations found

Comparison Of Quasi-Steady State And Dynamic Simulation Approaches For The Calculation Of Building Energy Needs: Thermal Losses

One of the aims of the European Directive 2010/31/EU (formerly 2002/91/EC) is to reduce the energy consumption of buildings introducing an energy labeling protocol which is expected to capture the attention and reorient the market, sustaining the diffusion of more efficient solutions. In order to evaluate the building energy performance, either analytical approaches or enhanced simulation tools are allowed. The coherence of the methods is important in order to avoid misleading results which can affect the evaluation by the market and eventually compromise the Directive effectiveness. The European Standard EN ISO 13790:2008 suggests to use the dynamic simulation in improving and tuning the quasi-steady state method proposed, and in particular to refine the correlation used to calculate the utilization factors (i.e., the dynamic parameters which reduce the thermal gains for heating need calculation and the thermal losses for cooling). Many efforts in calibrating the EN ISO 13790:2008 led to some changes on the correlations proposed in order to adapt the method to the climatic conditions, especially for the cooling season, and the building stock’s characteristics in different countries, but large discrepancies have been found. Differently from the previous works, the authors analyze the discrepancy sources focusing firstly on thermal losses, instead of considering directly the final result in term of energy needs. In this paper, the deviations between the thermal losses are evaluated, by means of an extensive use of simulation, analyzing a set of a 960 configurations obtained by the factorial combination of different values for the building shape, envelope insulation and composition, window type and size, ventilation rate and climatic conditions. Six different setpoint conditions were considered for the simulations. The analysis allowed the authors to identify the relevance of the deviations and to suggest ways to improve the correspondence between simulation and quasi-steady state methods in tuning processes

Classification of European Climates for Building Energy Simulation Analyses

Several studies couple simulations of building systems and statistical techniques in order to draw findings which can be generalized under given constraints. To this extent, one of the most important inputs to deal with is climatic conditions: indeed, the weather data and the localities chosen for the analysis can seriously affect the representativeness of the simulation outcome with respect to other regions. Nevertheless, the first question we should answer regards the domain to which one or few reference climates should be representative. As a common practice, national guidelines, heating and cooling degree-days scales and worldwide recognized climatic classifications are adopted. However, in some cases, these kinds of categorization are suitable only for specific applications. For example, the well-known and used Köppen-Geiger classification with the later Trewartha’s modifications is based on annual or seasonal air temperatures and cumulative precipitation and highlights mainly the relationship between climate and vegetation. Consequently, while this classification can be very effective to distinguish ecological systems, it can be insufficient for building energy analysis. Similar considerations apply to ANSI/ASHRAE 90.1 and 90.2 classification. In this work, we propose a critical discussion of the main climate classification system adopted in Europe and present a clustering and classification analysis on 66 European locations. The aim is to identify a limited number of climatic zones and, for each one, a reference climate to be used for energy simulations. The hourly weather data of dry bulb temperature, relative humidity and global horizontal irradiation reported in typical and reference years have been used as input. The clustering analysis has been performed with two approaches with different levels of complexity: (1) a simplified approach based on the calculated monthly averages of the weather variables and (2) a more detailed one based on the hourly profiles, through non-parametric techniques such as the Kolmogorov-Smirnov test. The obtained climatic classes have been compared to Köppen-Geiger traditional ones, underlining the main changes and the impact for building energy simulation analyses

The effect of ambient moisture conditions on heat flux time shift and decrement factor of multi-layered walls

Thermal properties of the opaque building envelope components are crucial for limiting the energy needs of a building. In particular, dynamic thermal properties of envelope components can significantly contribute to the minimization of heat transfer through the envelope and to the appropriate utilization of the internal and solar gains. This is particularly important in the cooling operation, especially in hot climates. Previous experimental and numerical studies on the determination of dynamic thermal parameters of opaque building components neglected the influence of moisture conditions prevailing within the ambient climate. This paper utilizes a calibrated and validated dynamic heat and mass transfer model to analyse the impact of ambient moisture conditions on the determination of dynamic thermal parameters. Time shift and decrement factor are determined for different wall structures (internally insulated or externally insulated) with regard to different outdoor climatic conditions (dry and humid climate). The impact of moisture conditions on the results is analysed and assessed. The results of this study clearly show that the effect of ambient moisture conditions on time shift and decrement factor can be significant and that an application of purely thermal models will lead to inaccurate predictions of the dynamic thermal behaviour of building components

Refrigerant R410A Vaporisation Inside a Small Brazed Plate Heat Exchanger

This paper presents the experimental heat transfer coefficients and pressure drop measured during refrigerant R410A vaporisation inside a small brazed plate heat exchanger: the effects of heat flux, refrigerant mass flux, saturation temperature and outlet conditions are investigated. The experimental results are reported in terms of refrigerant side heat transfer coefficients and frictional pressure drop. The heat transfer coefficients show high sensitivity both to heat flux and outlet conditions and weak sensitivity to saturation temperature. The frictional pressure drop shows high sensitivity to refrigerant mass flux and weak sensitivity both to saturation temperature and outlet conditions. The experimental heat transfer coefficients are also compared with two well-known correlations for nucleate pool boiling: a fair agreement is found

An Efficient Global Optimization Scheme for Building Energy Simulation Based on Linear Radial Basis Function

Motivation: The building performance optimization is considerably increasing since the design goals are moving from the solely energy saving target to the optimization of the overall performances, cost and sustainability objectives. The evolutionary algorithms coupled with building simulation codes are often used in academic researches, however, they are limited applied in actual building design. Indeed, the high number of expensive simulation runs required by evolutionary algorithms strongly limits their suitability for the professional practice. For this reason, an efficient optimization scheme is essential for the diffusion of the building performance optimization tools outside the academic world. What was done: The research focuses on the development of an efficient global optimization scheme (EGO) based on a radial basis function network (RBFN) meta-model to emulate the expensive function evaluation by means of the building energy simulation. In this surrogate model, each cost function can be approximated by a linear combination of unknown coefficient multiplied by a set of linear radial-basis function. In the proposed method, the surrogate model is firstly used in the evolutionary algorithm code to find the optimal solutions. Then, the actual fitness functions are evaluated for the optimal points by means of building simulation and the surrogate model is then update. These steps are continued until the convergence criterion is met. This efficient optimization scheme has been implemented in Matlab and verified on some test cases. The test bed of the method is the optimal building refurbishment of three simplified existing buildings, for which the optimal solutions have been also calculated by using the brute force approach. Finally, the EGO performances were also compared with those offered by the popular Non Sorting Genetic Algorithm (NSGA-II). Expected benefits of what was done: The results of this research show how the EGO algorithm is able to find a large number of optimal solutions with a reduced number of expensive simulation runs. This makes it possible to apply the algorithm to the optimization of building projects that use expensive simulation codes such as lighting models, CFD codes or coupled dynamic simulation of building and HVAC systems

Optimization of government subsidization strategies for building stock energy refurbishment

The high initial investment required in existing building refurbishment can limit the initiative of the building owners and prevent the full exploitation of a huge energy saving potential. Public incentives can play an essential role in fostering the energy retrofitting of the existing buildings and in increasing the renovation rate of the building stock, effectively reducing the energy final uses, the dependence on the fossil fuels, and helping meet the national efficiency targets. Public subsidization are intended to enhance the economic performance in terms of global cost of the energy efficiency measures for the owner, in order to induce positive actions and move optimality from low to high energy efficient solution. In contrast, the overall economic efficiency is obtained with combinations of interventions, able to achieve a certain energy saving target for the entire building stock at the minimum initial Investment Costs (IC). This paper tries to identify the overall economic efficiency in reducing the energy consumption of the existing stock and compares it with the efficiency of solutions optimal from the owner’s perspective, in order to support more efficient subsidization strategies. Different mixes of three reference building archetypes, representative of the existing buildings, are considered to define different possible stocks, in order to analyse their impact on the efficiency of energy renovation solutions. Four groups of energy efficiency measures (EEMs) dealing with respectively the opaque envelope insulation, the windows substitution, the heat generating system replacement, and the mechanical ventilation introduction are defined and their combinations considered

Development of a shoeboxing approach for Urban Building Energy Modeling

Urban Building Energy Modeling aims at assessing the building energy performance at city scale with as little computational effort as possible. Thus, different methods have been developed in the last years to reduce the required calculation time by simplifying the modeling approach, selecting only representative buildings, or minimizing the building description. Starting from the latter ones, this work proposes a novel algorithm capable of abstracting a randomly shaped building into a representative shoebox. The presented shoebox generation algorithm is based on a preliminary sensitivity screening analysis on a set of reference parallelepiped-shaped thermal zones. This allowed the identification of the most significant geometry indicators influencing the building’s performance. Based on this, more complex geometries have been simplified to the shoebox with the same indicators and the accuracy of the algorithm has been evaluated comparing the simulated performance of simplified and original buildings. The approach includes the definition of equivalent shading surfaces, to account for self-shading elements in the original building geometry. The algorithm has shown good accuracy not only on the hourly thermal loads, but also the zones’ hourly temperature profiles, reducing to one third the energy simulation time with respect to the detailed building model. Although not as fast as other urban modelling approaches in the literature, it can retain accurate results at a finer time scale, i.e., on hourly basis, which is necessary in applications such as district heating and energy networks