Modeling the internal dynamics of energy and mass transfer in an imperfectly mixed ventilated airspace (original) (raw)

Modelling and control of heat transfer phenomena inside a ventilated air space

Energy and Buildings, 2005

In this paper a data based mechanistic (DBM) model is proposed using a simplified heat balance formulation for modelling the temperature distribution inside a full scale ventilated room. The model has a number of parameters which are physically meaningful and determined using time temperature data obtained from experiments for several inlet air flow rates. At the inlet a step input in air temperature is applied and temperature responses at 36 sensor locations were recorded. For all ventilation rates used, the parameters of the model are extracted using statistical identification technique. Later, model based predictive control (MBPC) algorithm is developed to control temperature profiles on pre-selected sensor locations. The developed DBM model is compact in structure and found to capture the temperature distribution with high accuracy. The MBPC, which is distinguished by explicit use of process models, is robust for disturbance and noise effects. Besides it has high tracking capability of the reference trajectory. #

Modelling of heat and moisture transfer in buildings: II. Applications to indoor thermal and moisture control

Energy and Buildings

The overall objective of this work is to develop an accurate model for predicting heat and moisture transfer in buildings including building envelopes and indoor air. The model is based on the fundamental thermodynamic relations. Darcy's law, Fick's law and Fourier's law are used in describing the transfer equations. The resultant nonlinear system of partial differential equations is discretised in space by the ®nite element method. The time marching scheme, Crank±Nicolson scheme, is used to advance the solution in time. The ®nal numerical solution provides transient temperature and moisture distributions in building envelopes as well as temperature and moisture content for building's indoor air subject to outdoor weather conditions described as temperature, relative humidity, solar radiation and wind speed. A series measurements were conducted in order to investigate the model performance. The simulated values were compared against the actual measured values. A good agreement was obtained. #

Numerical Analysis of Air Exchange Between two Enclosed Spaces

Research Square (Research Square), 2022

The air quality problem has never been so acute as in this period of COVID-19. The three-dimensional modeling of thermo-aeraulic transfer in buildings is characterized by its complexity due to the large dimensions and the behavior's laws problem of the uids to be adopted. The number of nite elements increases with the processed volume, negatively impacting CPU time. Well-conducted numerical modeling can be more advantageous than an expensive experimental study requiring signi cant equipment, an extensive testing campaign, a large staff, and time. This work is aimed to carry out numerical modeling of an existing experimental device to simulate the effects of ventilation systems. We used the Computational Fluid Dynamics (CFD) code FLUENT. The results obtained showed good agreement with previous experimental data. A good correlation was obtained by analyzing temperature and velocity pro les in stationary and variable regimes. This validated modeling of the problem allows us to consider later, with su cient con dence, reliable simulations of several other cases of air transfer to achieve new human comfort and health conditions.

Modeling of Water Vapor Sources in Enclosures

International Journal of Structural and Civil Engineering Research, 2015

The objective of this study is to propose an approach concerning the integration of indoor humidity sources in CFD (Computational Fluid Dynamics) simulations for buildings. The numerical model is based on source terms of mass and energy, added in the conservation of water vapor equation and energy balance equation. The equation governing the conservation of water vapor is added to the basic equations dealing with turbulent non-isothermal confined air flows in CFD models. This method allows achieving values of air velocity, air temperature and air humidity (relative humidity or moisture content) all over the computational domain. The methodology is exemplified for the case study of an office with mixing ventilation system, the sources of humidity being represented by people. The results of this study can be used in analyses focused on thermal comfort and indoor air quality. Finally, the numerical description of water vapor sources proposed here can be easily extrapolated for other indoor humidity sources.

Modelling mass transfer phenomena and quantification of ventilation performance in a full scale installation

Building and Environment, 2005

This paper outlines development of a low order model that can be used for control purposes and quantification of ventilation performance in ventilated systems. First informative pollutant transport data is generated using numerical simulations. Later on, identification procedures are followed to build a low order transfer function model from the CFD generated input-output data. The obtained results demonstrate that first order model can sufficiently describe the dominant mass transfer dynamics in the ventilated air space. Afterwards classical mass balance equation is used to explain the objectively formulated model in a meaningful manner. The developed model is compact in structure and accurate in nature making it an ideal input for model based controller algorithm development. Furthermore its model parameter is found to be an inverse of the local mean age of air. Therefore the model can also be used to assess ventilation performance. r

Data-based mechanistic modelling of three-dimensional temperature distribution in ventilated rooms filled with biological material

Journal of Food Engineering, 2008

In this paper, a data-based mechanistic modelling approach was developed to real time monitoring and online adaptive control of three-dimensional temperature distribution in both an individual biological product and in a given movement. Boxes of potatoes were used as biological material. During the experiments, step inputs on an air inlet temperature were applied while airspace and potatoes temperature were recorded. The simplified refined instrument variable algorithm was used as a model parameter identification tool to obtain the best model order and parameters. By model compacting, several physically meaningful parameters were found to present the temperature distribution between the products and the airspace. A third order transfer function from the dynamic response of airspace from inlet air temperature with a high coefficient of determination R 2 T > 0:9 À Á and a low standard error (SE < 0.01) explained the heat exchange in a system. Two physically meaningful parameters were found from the model parameters. A local volumetric fresh air concentration b 1 was defined to the temperature distribution in the airspace, and a local 'cooling rate' a 2 was presented for the product temperature distribution. The values of b 1 and a 2 existing in the model could be used to design a control system for real time monitoring and online adaptive control of three-dimensional temperature distribution in the process room.

On the applicability of the heat and mass transfer analogy in indoor air flows

International Journal of Heat and Mass Transfer, 2009

The heat and mass transfer analogy is used in building simulation to convert heat transfer coefficients into mass transfer coefficients. The analogy is valid under strict conditions. In this paper CFD is used to investigate the accuracy of the analogy for indoor air flows when not all these conditions are met. CFD simulations confirm the possibility of applying the analogy to indoor air flows and show that when not all conditions are met, the average mass transfer coefficients remain well predicted by the analogy while the prediction of local transfer coefficients can result in large errors.

Simulation of flow and heat transfer in enclosed environments using a 2 f − υ model

Résumé: Dans ce papier, le modèle de turbulence 2 f − υ est employé pour la simulation d'une ventilation thermique d'une cavité. Les modèles k-epsilon RNG et SST k-ω sont aussi considérés afin de mener à bien une confrontation complète avec des données disponibles dans la littérature. Les champs de vitesses et de températures moyens sont en bon accord avec ceux de la littérature. Grâce aux résultas obtenus, nous pouvons stipuler que le modèle 2 f − υ est adéquat. Cette conclusion est confirmée en utilisant l'analyse des erreurs pour chaque profil dans les deux cas. Abstract: In this paper, the 2 f − υ model is employed for the numerical simulation of a cavity with an effect of thermal ventilation (hot airflow and cold airflow). Two numerical models, a RNG k-ε model and a SST k-ω model, are also used for a confrontation from the available data in the literature. The fields of averaged velocities and averaged temperatures predicted give generally agreement with available d...

Simulation of coupled heat and moisture transfer in air-conditioned buildings

Automation in Construction, 2009

The simultaneous heat and moisture transfer in the building envelope has an important influence on the indoor environment and the overall performance of buildings. In this paper, a model for predicting whole building heat and moisture transfer was presented. Both heat and moisture transfer in the building envelope and indoor air were simultaneously considered; their interactions were modeled. The coupled model takes into account the main hygrothermal effects, like moisture sources and sinks inside the room, moisture transfer through the envelope, vapor sorptiondesorption at the exterior and interior wall surfaces, heat sources and sinks inside the room, heat input from the envelope, the solar energy input through walls and windows, and hygrothermal sources or sinks due to the air-conditioning system. The new model was implemented in MATLAB-Simulink, and was validated by using a series of testing and validation tools.

Coupling of differential CFD and integral human thermophysiology numerical models applied in indoor ventilated spaces

E3S Web of Conferences, 2021

This work presents the development of the coupling of differential Computer Fluid Dynamics and integral human thermo-physiology numerical models applied in indoor ventilated spaces. The study is performed in a virtual chamber, similar to an existing experimental chamber, with dimensions of 4.50×2.55×2.50 m3. The chamber, occupied with twelve virtual manikins, is equipped with six tables, twelve chairs, one exhaust system and one inlet system, based on confluents jets system. In the exhaust system, they are considered six air ducts, located above the head level, connected to the ceiling area. The inlet system, based in four vertical ducts, with 0.15 m diameter, located on the corners of the chamber, is equipped with consecutive holes, that promotes horizontal jets near the wall. The results demonstrate that when the airflow rate increases the air quality number increases, the thermal comfort number decreases, and the Air Diffusion Index increases slightly. The predicted percentage of...