Tudor Baracu

This article considers a new type of air infiltration through building envelopes caused by the barometric pressure variation. This process is independent from wind action or stack effect. A new building–atmos-phere differential equation of air exchange is established. Based on the solution of the differential equation of air exchange, we propose the notion of pressure equilibration time 50 that characterizes the dynamic response of the building. Furthermore, experimental climatic data were processed using Fourier analysis methods in order to build an identification model based on the regular harmonics of external pressure oscillation. The barometric pressure reconstructed in its parameterized form was introduced in the differential equation of air exchange as a term that models the dynamics of the external action. The analytic solution of the differential equation of air exchange demonstrates that the indoor–outdoor pressure difference is insignificant at less than 10 À3 Pa for any harmonic of the external pressure variation. At the same time, it is concluded that the airtightness of the envelope has little influence on the process, as the indoor–outdoor pressure equilibration is almost instantaneous in a continuous regime of variation. The described mechanism of air infiltration explains the alternation of infiltration and exfiltration of air in buildings. For this, a mass balance of air exchange for the specific ranges of time is performed. We prove that the barometric pressure variation has an effect that accounts for 3.19% of the total quantity of air exchanged. The advances provided by this paper constitute a useful instrument for further studies concerning the stack effect in thermal dynamic conditions. Practical application: The paper proposes a novel methodology of determining the air exchange build-ing–environment by considering a new component of infiltration and its cyclic variation: the barometric pressure. A new mechanism of natural air infiltration is determined and modeled and it should be added to the existing ones: wind action and stack effect. A complete methodology of analysis and extraction of the cyclic processes hidden in an envelope of stochastic variations is defined and applied with the support of signal processing techniques and spectral analysis. The refinement of the mathematical instrument was able to distinguish through a deterministic approach an influence of 3.19% of the new barometric component. Furthermore, with few adaptations, the methodology constructed in this study can be applied for investigation of the stack effect by considering the cyclic variation of the atmospheric temperature. Currently, the stack effect is analyzed only for average conditions of temperature, a simplistic approach that suggests a large potential for further improvement.

This paper proposes a new extended power law (EPL) of air infiltration in buildings as an alternative in certain cases to the widely used power law (PL) and quadratic law (QL). Specifics: it separates the airflow rates in laminar and turbulent components; improves the estimation of the leakage area; new evaluation of the airflow rate at low pressure differences. In various numerical comparisons several advantages of EPL are revealed and we appreciate that will raise interest and adoption by the software platforms that evaluate the airflow in buildings. Based on the measurement data (MD) of the Passive House Politehnica from Bucharest (Romania), EPL is validated and compared with other laws of infiltration. Four statistical indicators (PCC, RMSE, MBE and MAE) show that EPL has the best fit to MD. A generalized function of air leakage is developed and may serve in certain cases for a higher level of processing the MD for improved evaluations. An inverse problem approach finds the leakage area of the cracks in linear-perimetral and in circular-compact distributions respectively. They are alternative to the consecrated notions ELA and EqLA. The leakage areas are estimated to be from 5 cm 2 (the case of LFCorrLA* 1 in circular-compact formulation) up to 2085.7 cm 2 (the case of LFCorrLA at in linear-perimetral formulation). Among the surveyed leakage areas we appreciate that CorrLA offered the most realistic result. Through linear extrapolation of the laws of infiltration at low pressure difference EPL is compared with PL and QL and the differences are discussed.

This study aims to integrate in constructal networks of heat exchangers (HEXs) two ways of optimization represented by entropy generation minimization and thermoeconomics. We obtained a complete (non-simplified) analytic solution of the entropy generation along of the HEX that allows exact evaluation of the irreversible processes in smooth or augmented tubes. By using this analytic solution, we proposed an adapted augmentation entropy generation number and compared it with Bejan's original formulation. We evaluated the difference between the two at more than 7%. For a heat exchanger with corrugated tubes we have found that the recommended augmented solution e4p4a45#9 in Bejan's adapted formulation is different from the e2p4a45#3 recommended by Bejan's original formulation; thus, we found a change of the hierarchy of the recommended solutions. We developed a thermoeconomic model of a HEX for periods of operation of 1 to 10 years, for which specific optimum points of cost have been obtained. Furthermore, representing the cost versus entropy generation opens the path for future advanced comparisons of complementary objectives that may conduct to balanced designs: thermal process optimum vs economical optimum. We outlined, through matrix formulation, a new methodology of analysis of the constructal tree networks based on the network laws and thermo-hydroelectric analogy. The proposed methodology is characterized by compactness, a higher degree of abstraction of the problem and allows further generalizations. Moreover, it is suitable for advanced objectives like optimization, irreversibility analysis, sensitivity analysis or inverse problems.

This study proposes new matrix relationships of the radiative interactions in enclosures along with their corresponding applications. By means of several transformations one establishes matrix formulae based on equations of radiative exchanges containing variables defined in a discrete analog form, and further on, by means of a multidisciplinary approach, the solutions are organized in algorithms that use the theory of networks, graphs and electric circuits. The theoretical advancements consist in two different paths: the matrix formalism method (MFM) and the network analogy method (NAM). As a result of the advancements, a high degree of parameterization of the problem of radiative transfer in an enclosure is achieved and it facilitates superior physical interpretations at the level of the ensemble. It will be simple to use the developed methodologies in designs, balances and simulations.

ABSTRACT The today energy efficient buildings are mainly related only to the available standards when their performances are described. This approach is correct just in terms of formal qualification to meet the requirements of the statutory rules and give people confidence. Beyond these facts, todays energy efficient buildings have to be known not only in the context of the existing technology, but also in the evolution of the equipment and the design concept used in synchronization with the contemporaneity of the science. In this paper, a historical laborious presentation of the techniques and concepts evolution that lead to energy efficient buildings as we know them today, is presented. An overview of the modern approach for the design of the main elements of such type of buildings is also presented. The paper realizes a review of the current state of the energy efficient buildings, in terms of definitions and characteristics.

This study aims to obtain the information about the thermal characteristics of the Passive House of University POLITEHNICA from Bucharest, Romania. Modeling a house by using the method of thermal networks gives a way to find out the specific thermal reaction to the variable outdoor conditions. HVAC systems including their control have to synchronize with the thermal characteristics of the house expressed by the thermal reaction and heat consumption. The results of this study gives the information necessary to define, calibrate and optimize an adequate HVAC system with specific reaction and good prediction to the changing outer conditions in order to maintain a proposed thermal comfort with minimum energy consumption. Detailed analysis includes two scenarios: Free Running Mode (FRM) and Constrained Running Mode (CRM).
The main tool used for this analysis is the software package Matlab-Simulink.