Search

In this work, we present a study of the nonlinearity of building thermal behavior based on a metamodel for cooling energy needs. We studied the nonlinearity of the thermal behavior of an office. The building quadratic behavior and interactions between its components were analyzed based on the metamodel coefficients. The metamodel was fitted with a reduced number of dynamic simulations. The nonlinearity was first assessed as function of the mean outdoor air temperature in fifteen typical European climates and then as function of the internal heat gains for the coldest and hottest climates. The metamodel provided highly accurate results with fast calculation time. However, a higher accuracy was generally obtained for hot climates, high internal heat gains and lightweight thermal mass. Conversely, the nonlinearity of thermal behavior was accentuated in cold climates and with low internal heat gains. Moreover, the interactions between the building components were found to be more influential on cooling energy needs than quadratic behavior. We propose a classification of thermal behavior into three regimes: Highly nonlinear when the energy needs are close to zero; intermediate with decreasing nonlinearities that can be expressed by power functions; and finally, a quasi-linear regime with almost-steady nonlinearities.

The main objective of this study is to develop and test hybrid ventilation systems and control strategies that are suitable for residential buildings. Two ventilation systems were modelled: a mechanical extract ventilation system (called the reference system) and a hybrid low pressure ventilation system that can support two different types of demand control strategies (occupancy detection and C[O.sub.2] concentration). The newly developed models were assembled with the existing thermal models of the SIMBAD Building and HVAC Toolbox developed by the CSTB. A single family house located in Athens (Greece), Nice (France), Trappes (France) and finally Stockholm (Sweden) was considered as the case study. Yearly simulations were performed to assess the performance of the hybrid ventilation control strategies. The assessment criteria used are related to indoor air quality, thermal comfort, energy consumption and stability of control strategies. The results show that the low pressure ventilation system can improve the indoor air quality and reduce the fan energy consumption compared to the reference system while maintaining the same building energy consumption for heating. Keywords: Hybrid ventilation; Control strategies; Indoor air quality; Numerical simulation

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2005.06.015 Byline: Mirela Robitu (a)(b), Marjorie Musy (b), Christian Inard (a), Dominique Groleau (b) Keywords: Urban climate; Vegetation; Water pond; Thermal comfort Abstract: The beneficial influence of trees and water ponds on summer comfort in urban spaces was studied experimentally in situ and in wind tunnels but the modeling needs further development to become effective in practical applications. This paper introduces a numerical approach based on coupling the CFD model of airflow, in which the influence of trees is considered as source terms, and the radiation exchange, completed with thermal conduction. The CFD, radiation and thermal conduction models use the same discretization grid at their common boundaries. The model was used to estimate the influence of trees and water ponds in a real town square. Comparison of results between two situations, with and without vegetation and water pond, indicate that surface temperatures are reduced in presence of trees and the comfort is improved. Author Affiliation: (a) LEPTAB University of La Rochelle, Avenue Michel CREPEAU, 17042 La Rochelle, France (b) CERMA -- Architectural School of Nantes, Rue Massenet, BP 81931, 44319 Nantes, France Article History: Received 3 January 2005; Revised 31 May 2005; Accepted 28 June 2005 Article Note: (miscellaneous) Communicated by: Associate Editor Matheos Santamouris

A neuro-human thermal model was optimized to increase the prediction accuracy of the physiological variables of a group of 15 healthy male students exposed to transient environmental conditions. The effect of both the passive and active systems parameters was studied using a sensitivity analysis, and the parameters that had the most influence on the neuro-human thermal model outputs were established. A genetic algorithm was then used to optimize the model in order to determine the parameters that corresponded to the studied population. The results showed that the optimization increased the precision of the neuro-human thermal model. The mean absolute error and the maximum error between the experimental data and the numerical results for mean skin temperature were 0.13°C and 0.56°C, respectively, and we obtained 0.03°C and 0.11°C, respectively, for rectal temperature. These results show that the neuro-human thermal model can be accurately adjusted for the rectal, mean and local skin temperatures of a targeted population by using a genetic algorithm to determine the values of the parameters that correspond to this population. [ABSTRACT FROM AUTHOR]

In this study, a metamodel for cooling energy consumption is presented. In constructing the metamodel, the assumption was made that cooling energy consumption is a polynomial function of the energy consumption of each individual building component. We studied the cooling energy consumption of an office under various climate conditions and with different thermal masses and uses. The metamodel was fitted from dynamic simulations by multiple regression analysis and the accuracy obtained was very close to that of dynamic simulation. Our study highlights the value in using the Design of Experiments method to fit the metamodel since the number of simulations could be reduced without a loss of accuracy. The metamodel coefficients were analysed to gain insight into the thermal behaviour of a building. We found that the energy consumption for cooling was a convex function of the individual energy consumptions of the building components. The results suggest that it would be beneficial to study third order and exponential terms. This work opens a path to a new way of analyzing building energy performance. [ABSTRACT FROM AUTHOR]

Thermal comfort is a primary concern of building design. Accurate and rapid methods are needed to assess thermal comfort in non-air-conditioned buildings. In this work, a new flexible metamodel was developed for assessing long-term thermal comfort in non-air-conditioned buildings. Using five different indices, the metamodel was used to study the thermal comfort in an office during summer for two typical cold and hot European climates. The metamodel was fitted by multiple regression analysis with a low number of dynamic simulations using the design of experiments. A good fit was obtained for indices, such as maximum indoor temperature, that are consistently sensitive to the influencing factors. For the remaining indices, such as overheating degree-hours, the accuracy was dependent on the location and thermal mass of the building. An interpolation method was proposed that can be used when the metamodel fit is not good. This method gave accurate results with all the indices (R2 > 0.98) when the values were obtained from the mean indoor temperature without additional computational efforts. The proposed metamodel could be used to rapidly assess long-term thermal comfort and to understand the relationships between building design and indoor thermal conditions. [ABSTRACT FROM AUTHOR]

Occupant behaviour is now widely recognized as a major factor in the disparity between predicted and measured building performance. Stochastic models are a convenient way to model the rational, diverse and complex nature of occupant behaviour, including presence and adaptive behaviour. The FMI standard was used to co-simulate the building energy modelling program EnergyPlus and a multi-agent platform that contains stochastic models in an integrated environment. Using an office building as a case study, we show that data mining, through a correlation matrix and a principal component analysis, was an efficient way of investigating the cumulated influence of occupant behaviour on energy performance. The organisation of simulations was achieved using design of experiments in order to take into consideration multiple building configurations. This paper demonstrates how data mining of stochastic simulations can be used to identify the determinants that have the greatest influence on building energy needs. [ABSTRACT FROM AUTHOR]

Following development and validation of the Solene-microclimat tool, the model was used to compare the impacts of various “greening strategies” on buildings’ summer energy consumption and indoor comfort. The studied strategies were greening walls, roofs, and ground (lawns). Solene-microclimat enables to simulate simultaneously a building's thermal behavior and the microclimate at the district scale, with the retroaction of buildings on climate. Distinguishing between direct (due to the modification of building’ characteristics) and indirect impacts (due to the modification of boundary conditions) of these surfaces is also possible. Thus, the strategies were successively implemented on the studied building, the surroundings, and both of them. The simulations were carried out using Solene-microclimat considering insulated vs. non-insulated buildings. Findings confirm that the direct and indirect effects of theses surfaces are almost negligible on insulted buildings. For non-insulated ones, green walls have a direct effect on indoor comfort throughout the entire building, whereas the effect of green roofs is primarily confined to the upper floor. Moreover, the indirect effect of a green wall is greater, mainly due to the drop in infrared emissions resulting from a lower surface temperature. It has also been proven that the indirect effects of green walls and surrounding lawns can help reduce the loads acting on a non-insulated building. Direct and indirect effect can’t be directly added. This is particularly interesting for heritage buildings or highly glazed ones the refurbishment of which is often difficult. [ABSTRACT FROM AUTHOR]

Following development and validation of the SOLENE-microclimat tool, the underlying model was used to compare the impacts of various "greening strategies" on buildings' summer energy consumption and indoor comfort. This study distinguishes between direct and indirect impacts by successively implementing the test strategies on both the studied building and surrounding ones; it also considers insulated vs. non-insulated buildings. Findings indicate that green walls have a direct effect on indoor comfort throughout the entire building, whereas the effect of green roofs is apparently primarily confined to the upper floor. Moreover, the indirect effect of a green wall is greater, mainly due to the drop in infrared emissions resulting from a lower surface temperature. It has also been proven that the indirect effects of green walls and surrounding lawns can help reduce the loads acting on a non-insulated building. [ABSTRACT FROM AUTHOR]

The aims of this study are to highlight the microclimatic phenomena to which the energy consumption of a building is the most sensitive and to compare different approaches to coupling microclimate and building energy simulation models. We first present a study in which spatial variations in outdoor air temperature are not taken into account so as to compare the relative effect of convective and radiative heat flux on the outer surface energy balance. Then, several coupling methods are implemented, for which energy consumption in winter and indoor temperature in summer are compared between insulated and non-insulated buildings. Results show that for the urban context, taking into account long-wave radiative heat fluxes is crucial. Moreover, representing local modifications in outdoor air temperature is necessary for non-insulated buildings in summer, but can be neglected in winter. In conclusion, an intermediate coupling method that can be used under certain assumptions is proposed. [ABSTRACT FROM PUBLISHER]

Thermal energy storage in buildings is essential to reduce energy consumption, to switch electrical consumption from on-peak period to off-peak period and to develop the use of intermittent renewable energy sources. Several systems designed to store thermal energy on a short-term scale (maximum a few days of storage) are presented in previous publications. However, there are no available comparisons of these systems and their conditions of use. This paper details these different designs for short-term scale thermal energy storage, regarding (i) their passive or active nature, (ii) their usage conditions and (iii) their performances. In the first section, the thermal properties of materials are listed. In particular, advantages and problems associated with phase change materials are presented. Subsequently, thermal storage systems are presented in two parts, on the one hand, passive systems and on the other hand active systems, according to the fluid used. For each system, the advantages of substituting sensible storage with latent storage are highlighted. Furthermore, an original and comparative analysis of published studies attempts to define some criteria and requirements for efficient use of latent storage. This review demonstrates that an exhaustive comparison of the systems encounters difficulties, due to the differences between the studies with respect to experimental measurements and weather data and the lack of similar comparison criteria, such as decrement factor, efficiency and cost. [ABSTRACT FROM PUBLISHER]

This paper presents a new air-heating system concept for energy-efficient dwellings. It is a system designed to heat a low-energy building by coupling a heat-recovery ventilation system with a three-fluid heat exchanger located on the chimney of a wood-pellet stove. The proposed work focuses on the heat transfer that occurs between flue gases, the ventilation air and the combustion air within a triple concentric tube heat exchanger with no insulation at its outer surface. The main objective is to predict outlet temperature for the specific geometry of the heat exchanger studied here. Thus, the governing differential equations are derived for a counter-co-current flow arrangement of the three fluids. Then analytical solutions for the steady-state temperature distribution are obtained as well as the amount of heat transferred to the outside. An expression for the effectiveness of the heat exchanger is also proposed. Based on these results, calculations are performed on a case study to predict the fluid temperature distribution along the heat exchanger. Finally, a parametric study is carried out on this case study to assess the influence of the relevant parameters on the effectiveness of the heat exchanger. In addition, computation of heat losses to the outside justifies whether insulation is needed. [ABSTRACT FROM AUTHOR]

In this paper, experimental tests conducted on a new wood-based air-heating system for energy-efficient dwellings are presented. The main objective is to evaluate the resulting outlet temperatures and the amount of heat recovered by the ventilation air in order to assess feasibility and performance of coupling a mechanical ventilation heat-recovery unit and a triple concentric tube heat exchanger integrated into the chimney of a room-sealed wood-pellet stove to heat an entire house. After introducing the context of this work, the three main components of the combined system developed here, the coupling configuration adopted, as well as the protocol used and the sensors implemented on an experimental setup carried out in a laboratory are detailed in turn. Then, the heat transfer rates obtained from measurements for the various fluids as well as the effectiveness of the heat exchangers are presented and discussed. Finally, the resulting outlet temperatures of the three fluids exchanging in the triple concentric tube heat exchanger studied here are compared to those provided by analytical solutions obtained with a mathematical model. It is shown that heat transfer rates are predicted with a relative difference that is lower than 5% compared to experimental values and that such a system enables to cover all or most of heat losses in an energy efficient building. [ABSTRACT FROM AUTHOR]

In the consideration of building energy performance and urban climate models, irradiation is a key parameter. From the city scale to the detailed building interchange, different approaches and models with various levels of details are explained in this review, and their scope and usefulness considered. The first part of the study deals with solar and longwave sky irradiance models. Six models of sky diffuse irradiance are presented, together with details of the models of longwave sky irradiance. At city scale, the influence of an urban area on the atmospheric radiative budget requires knowledge of the radiative flux leaving the urban area. Albedo and longwave reflectivity models are detailed in the second part to determine shortwave and longwave fluxes from urban areas. Solar access quantifies the shortwave radiative energy received by an urban surface for a specified period, determined by the building's scale and type of facade. Depending on the urban morphology, tridimensional city models are presented in this section to compute the solar access. In order to calculate the energy budget of building walls, the radiation interchanges in the district have to be coupled with other physical phenomenon. Thus, some simplifications and various models to reduce computation time are discussed. [ABSTRACT FROM PUBLISHER]

With increasing mean and extreme temperatures due to climate change, it becomes necessary to use—not only future typical conditions—but future heatwaves in building thermal simulations as well. Future typical weather files are widespread, but few researchers have put together methodologies to reproduce future extreme conditions. Furthermore, climate uncertainties need to be considered and it is often difficult due to the lack of data accessibility. In this article, we propose a methodology to re-assemble future weather files—ready-to-use for building simulations—using data from the European Coordinated Regional Downscaling Experiment (EURO-CORDEX) dynamically downscaled regional climate multi-year projections. It is the first time that this database is used to assemble weather files for building simulations because of its recent availability. Two types of future weather files are produced: typical weather years (TWY) and heatwave events (HWE). Combined together, they can be used to fully assess building resilience to overheating in future climate conditions. A case study building in Paris is modelled to compare the impact of the different weather files on the indoor operative temperature of the building. The results confirm that it is better to use multiple types of future weather files, climate models, and or scenarios to fully grasp climate projection uncertainties. [ABSTRACT FROM AUTHOR]