Abstract
The underground air tunnel system shows promising potentials for reducing energy consumption of buildings and for improving indoor thermal comfort, whereas the existing dynamic models using the computational fluid dynamic (CFD) method show computational complexity and are user-unfriendly for parametrical analysis. In this study, a dynamic numerical model was developed with the on-site experimental calibration. Compared to the traditional CFD method with high computational complexity, the mathematical model on the MATLAB/SIMULINK platform is time-saving in terms of the real-time thermal performance prediction. The experimental validation results indicated that the maximum absolute relative deviation was 3.18% between the model-driven results and the data from the on-site experiments. Parametrical analysis results indicated that, with the increase of the tube length, the outlet temperature decreases with an increase of the cooling capacity whereas the increasing/decreasing magnitude slows down. In addition, the system performance is independent on the tube materials. Furthermore, the outlet air temperature and cooling capacity are dependent on the tube diameter and air velocity, i.e., a larger tube diameter and a higher air velocity are more suitable to improve the system’s cooling capacity, and a smaller tube diameter and a lower air velocity will produce a more stable and lower outlet temperature. Further studies need to be conducted for the trade-off solutions between air velocity and tube diameter for the bi-criteria performance enhancement between outlet temperature and cooling capacity. This study proposed an experimentally validated mathematical model to accurately predict the thermal performance of the underground air tunnel system with high computational efficiency, which can provide technical guidance to multi-combined solutions through geometrical designs and operating parameters for the optimal design and robust operation.
Highlights
As a considerable energy consumer, building energy consumption has become one of the three major energy users all around the world, accounting for more than 30% of the total global energy consumptions [1,2,3]
In order to investigate multivariant impacts onlength, the outletmaterial, temperature and cooling capacity using of the UATcalibrated system, parametrical analysis has been conducted on inlet air temperatures, air system, velocities,the heat experimentally mathematical model
A dynamic mathematical model of the underground air tunnel system was developed on the MATLAB/SIMULINK platform for the dynamic performance prediction, together with an on-site experimental test-rig for the validation
Summary
As a considerable energy consumer, building energy consumption has become one of the three major energy users all around the world, accounting for more than 30% of the total global energy consumptions [1,2,3]. The commonly used mathematical models can be classified as the steady-state model and dynamic models based on the temperature variation of surrounding soil outside buried tubes with operation time [30]. With respect to the steady-state model of the UAT system as already developed in academia, the main drawback is ignorance of the variation of soil temperature for complex design and operation parameters [32]. During real operation of the UAT system, temperatures of heat exchange mediums (e.g., flowing air, tube wall, and surrounding soil) are dynamically and constantly changing, depending on the heat-transfer rate and the thermal capacity of the material. Systematic and parametrical analysis results indicated that the dynamic performance from the thermal transient response was highly dependent on the soil coefficient of heat conductivity and the time-duration for continuous operation.
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