CFD studies on stratum ventilation installed with a VRF/VRV system for tropic buildings / Umair Ahmed

Umair , Ahmed (2022) CFD studies on stratum ventilation installed with a VRF/VRV system for tropic buildings / Umair Ahmed. PhD thesis, Universiti Malaya.

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Abstract

In buildings, air conditioning and mechanical ventilation (ACMV) systems are the major shareholders of overall energy consumption. Energy-efficient designs of the ACMV systems for building applications are therefore needed. While designing an efficient ACMV system, consideration must be given to the growing concerns of enhanced thermal comfort and improved indoor air quality (IAQ). The variable refrigerant flow (VRF) system is a widely adopted alternative to the existing building cooling systems due to the higher energy efficiency and individualized temperature control feature. However, it suffers from shortcomings such as no outdoor air induction for ventilation and higher initial cost. Therefore, this work was intended to design the variable refrigerant flow (VRF) integrated stratum ventilation/air distribution systems for tropical buildings. Performance evaluation of different configurations of the integrated design is carried out in this study. To obtain an efficient air distribution terminal device for large tropical applications, different devices were experimentally and numerically investigated and compared. This study also presents the development and validation of a simplified nodal model that predicts the vertical temperature profile of the integrated design for large domain. The energy simulation models of the VRF-SV hybrid system using TRNSYS software were also developed in this study to compare the annual energy consumption of the fully integrated and decoupled designs of the VRF-SV system with multi-split AC systems and standalone VRF system. Lastly, the air distribution performance of the architecturally designed high-capacity linear diffuser in a large tropical atrium building is also evaluated in this work as a case study. Following a suitable design approach, the combined system provides better thermal comfort with enhanced indoor air quality and improved energy savings to relatively large space building. This system has also shown an excellent potential to be installed in any building regardless of the size and heat load. With a fully integrated design approach, a horizontal air jet at head level, a slight and reverse thermal gradient between the head and foot levels (ΔT1.5-0.1 = -2.85oC), and a low percentage of thermally dissatisfied people (<25%) are noticed under this investigation. The configuration 5 (wall exhaust configuration) showed overall good results in terms of thermal comfort indices. The doubled deflection grille was found most efficient air terminal type for providing throw to a larger distance. A good match is also observed in the simulated and modified nodal model’s calculations. Therefore, this model can be used for energy calculation and in practical engineering design. The TRNSYS simulation results of the energy use analyses of the ACMV system in the tropical building revealed that the decoupled design of the VRF-SV hybrid system could save a significant amount of energy compared to the other investigated systems. Results obtained from the case study revealed a relatively longer airflow jet at 0o blade angle through the high-capacity diffuser. Based on the above outcomes, the VRF-SV hybrid system was found as an energy efficient substitute of the conventional ACMV systems for tropical buildings.

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