Ismael R. Maestre

DESIGN METHODOLOGY AND COOLING POTENTIAL OF THE ENVIRONMENTAL HEAT SINKS

The usefulness of defining the cooling potential and other related variables is a function of how these figures will help the designer in the decision taking process. Consequently, a rational approach to these definitions should start from a certain design methodology The present paper proposes a design methodology which uses the concepts of gross cooling potential, net cooling potential, available cooling potential, usable cooling potential and natural cooling saving fraction. These concepts are expressed under common terms for three natural cooling techniques (NCT), radiative cooling via night sky radiators, ground cooling using buried ducts and evaporative cooling via mechanical evaporative coolers. The objective is to develop a systematic procedure of producing information about the suitability of using a certain NCT in a given locality and for a certain building. The application of the methodology mentioned for a set of European localities has been included in the ATLAS about the potential of NCT whi...

Improving direct solar shading calculations within building energy simulation tools

The calculation of the shadows that building environment, building elements or shading devices may cast on the building envelope, plays a key role in load calculations and building energy simulation. Algorithms for solar shading calculations have direct repercussions on the accuracy of the results and the computational times of building simulation tools. This paper presents an improved method for direct solar shading calculations based on the projection of every polygon on a unique receiving surface and incorporates recent and high efficient algorithms to solve polygon intersections. Firstly, the method is shortly described. Secondly, it is validated by comparisons with other methods, experimental results and European standards. Then, a comparison test between the proposed and conventional methods is presented to assess computational speed improvement. Finally, the main advantages of the proposed method are discussed.

Fitting conduction transfer function method to low Fourier numbers: application to ground-coupled floors

This paper proposes a practical solution to the problems arising when the conduction transfer function (CTF) method is applied to solve the 1D transient component of heat transfer in the internal zone of ground-coupled floors. The lower boundary condition for these problems must be imposed at a depth of several metres. The proposed method is based on the division of the ground domain into a number of layers that allows calculation of transfer function coefficients while keeping the first cross coefficient negligible. A mathematical expression is proposed for the proper layer thickness that assures the applicability of the CTF method to thick ground domains. A numerical validation for a slab-on-grade configuration has been carried out showing maximum errors of 0.09°C (0.42%) and 0.73 W/m2 (2.24%) for temperature and heat flow rates on the floor surface, respectively.

Evaluation of the Computation Times for Direct and Iterative Resolution Methods of MTJ Library Matrices Applied in a Thermal Simulation System

Thermal simulation systems in buildings, contribute to the design of energy-efficient structures; however, a significant amount of computational time is required in order to obtain the results of the simulation process. The main focus of this paper is examining the possibility of reducing time required for thermal simulation systems calculations. More specifically, the paper focuses on one of the major processes that requires computing resources at solving the system of equations obtained as a result of the thermal modeling of a building. This research was undertaken in order to determine the performance of Java library methods: Matrix Tool for Java (MTJ) for solving systems of linear equations, and identifying which of these was the optimum in terms of computation time. For this purpose, tests for the iterative methods combined with pre-conditioners were conducted. The tests of the direct method were done through the development of a software implemented in two case studies of buildings, and that was modeled with the parameters of the thermal simulation software called JEner, from the Thermal Engineering Research Group from the University of Cadiz in Spain.

Applicability of One-Dimensional Transient Solutions for Ground-Coupled Heat Transfer in Buildings

The ground-coupled heat transfer in buildings is a complex, transient and multidimensional problem. There have been many studies focused to obtain the heat flux in slab and basement foundations. Most of them include the multidimensional effects occur at the perimeter however there are situations in which the heat transfer is mainly one-dimensional. This paper presents a study that aims to establish the accurate of an analytical one-dimensional solution to estimate the ground-coupled heat transfer. Detailed simulation by using finite element software is used to obtain the total heat flux at indoor surface of the building for a whole year. Typical slabs and basements foundations for different dimensions have been analyzed. A correlation to estimate the relative error is proposed.

The Influence of Outer Weather Conditions on the Modelling of Vertical Ground Heat Exchangers

Policies for energy saving and carbon dioxide emission reduction have enouraged the use of efficient technologies in building thermal conditioning, like geothermal source heat pumps [. Most of the thermal models used to simulate the performance of vertical ground heat exchangers do not consider the effect of outer weather conditions, except for the setting of the initial ground temperature [. This paper shows a study to assess the effect of outer weather conditions on the outlet fluid temperature, especially during the upper part of the exchanger. Different depths for typical configurations of ground heat exchangers have been analysed. Detailed simulations have been developed for a full year of performance using a commercial finite volume computational fluid dynamics (CFD) code (©ANSYS-CFX). Outer weather conditions have been set by using synthetic hourly weather data and considering all of the heat transfer phenomena involved. Errors in outlet fluid temperature and surface borehole temperature have been estimated for the whole year of simulation.