Date of Award

December 2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical and Aerospace Engineering

Advisor(s)

Jianshun Zhang

Keywords

Building Energy, Computational Fluid Dynamics, Indoor air quality, Micro-environmental control, Semi-open space, Thermal comfort

Subject Categories

Engineering

Abstract

Local air delivery, heating, and cooling combined with local space partition and confinement (called semi-open space or SOS) have the potential to provide micro-environment that is tailored to the individual preference of the occupants, and hence increase the percentage of satisfied occupancy from currently 80% to near 100%. This research investigates the use of a micro-environmental control system (µX) and semi-open space (SOS) to efficiently provide the desired thermal comfort and air quality conditions for individual occupants while the ambient air temperature set-points were relaxed for reducing the overall energy consumption of the building. A computational fluid dynamics (CFD) model was developed and validated. The model in combination with the results from full-scale chamber experiments was used to evaluate the performance of proposed cooling/heating delivery system and the role of the SOS. During summer time, a cooler air was supplied locally. It was found that the cooling performance increased more by increasing the supply air flow rate than reducing the supply air temperature when the total cooling power is constant, and the cooling performance of the Air Terminal Devices (ATDs) was highly dependent on the shooting angle. The cooling efficiency increased dramatically with the supply air temperature. Also, both the CFD model simulation and experimental work has demonstrated that the heat loss by the manikin was sensitive to the distance between the diffuser and the manikin. However, this effect was also related to the clothing material on the manikin. During the winter time, the idea of heating a person with only a warm air jet was shown to be not efficient, but the confinement box was able to improve the heating performance by two to three times. A more ergonomically-friendly warming foot mat with a reflective box was very effective to restore people’s thermal comfort when the ambient space air was maintained at a lower temperature set-point for energy saving. The existence of the cubicle, as an SOS, significantly changed the airflow pattern in the office, and hence the thermal environment and air quality distribution. The cubicle could “protect” the occupants from the background air flow by reducing the average velocity as well as increasing the average temperature in the occupied space. The openness of the cubicle weakened the “protection” of the cubicle depending on the opening’s orientation and size. The “protection” may not be favored regarding thermal comfort and air quality when the emission is inside the cubicle, but it should be encouraged when the emission is outside the cubicle. The combination of the µX with the SOS can create an independent micro-environment regarding thermal comfort and air quality as well as maintain the privacy of the occupant. As a secondary goal, the ability of the CFD model to adequately predict the local heat transfer from the human body and its limitation were also investigated. The case without the µX compared better with the experiment than the case with the µX from the heat transfer point of view. The effect of the clothing material could be properly represented by a constant temperature difference or as a layer of thermal resistance. Moreover, it was found the fidelity of the surface temperature control for the manikin affected the validation of the CFD model. The concept of SOS was defined for the first time in this study and SOS’s role in shaping the microenvironment with and without local heat, cooling and ventilation were investigated both numerically and experimentally. The detailed CFD model developed has accurate representation of the effects of the manikin’s geometry and the effect of clothing thermal resistance on the boundary conditions for the CFD simulation, which can be used for the investigation of effects of air velocity, temperature, room air flow pattern and clothing on the local and overall average heat loss from human bodies and the resulting thermal comfort of the building occupants under various internal room and partition configurations.

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Open Access

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