Performance and Application Assessment on Glazed and Opaque Solar-absorbing Facades

新型透光與不透光太陽能吸收幕牆的性能及應用評估

Student thesis: Doctoral Thesis

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Award date24 Dec 2019

Abstract

The energy and environmental pressures make renewable energy utilization, especially solar energy, inevitable and attractive. Both the glazed and opaque building surface can work as the solar collector to absorb solar energy and reduce solar heat transmission to indoor space. In this study, the novel glazed and opaque solar-absorbing façade panels are proposed and their performance and application are investigated.

Concerning the glazed façade panel, liquid-filled window with submerged heat exchanger is a multi-glazing system filled with a heat-absorbing liquid layer, usually distilled water, in the window cavity. The heat exchanger is set horizontally at the top end of the window cavity and is fully submerged below the liquid level. Comparing with the previous buoyant-flow design, this liquid-flow window is more compact by removing the double-pipe heat exchanger, and also reduces the material use and costs. Under sunlight, the absorbed solar energy by the window can be taken away by the cold feed water flow without direct contact with the liquid in the window cavity. In this way, the flowing water is preheated and this window serves as a solar liquid-heating device. The decreased transmitted and reflected heat reduces the indoor air-conditioning demand in summer, and lessens the urban heat island burden of the city.

For the opaque façade panel, heat pipe array is proposed for use in the aluminum veneer curtain wall - so called the heat pipe embedded aluminum veneer curtain wall (HPeAVCW). A highly selective film attached on the outer surface of the aluminum plate allows most of the incident solar energy be absorbed by the array of heat pipe evaporators attached to the plate, as the thermal absorber. The absorbed solar energy is quickly transferred to the cold domestic water flowing inside the water box, where the heat-pipe condensers are inserted, and then the flowing water is preheated. Then, since the vertical height of the water chamber should be adequate to accommodate the straight condenser sections, heat pipe ring is proposed to replace the conventional straight heat pipe and the opaque wall becomes HPReAVCW. The upper inverted “U” inserted into the water chamber ensure enough condenser surface area for heat transfer. In this way, for a fixed height of the opaque façade panel, the height of the water box is reduced, and in proportion, the solar absorbing area is increased.

The thermal performances of the proposed glazed and opaque façade panels were studied through experimental testing and numerical simulation. The prototypes of the glazed and opaque façade panels were designed and constructed. The experiment of the two kinds of prototypes was conducted in Huizhou, Guangzhou province in mid-September 2018. The thermal performance of the solar-absorbing facades in the real environment was analyzed with the measured data. The day-time averaged water heat gain efficiencies of the glazed façade were 20.46%, 31.45%, and 24.65% on three consecutive days with different sunshine levels. For the opaque facades, they were 25.2%, 28.8%, and 30.8% for HPeAVCW, and 34.4%, 37.9%, and 38.0% respectively for HPReAVCW on the same consecutive days. For the liquid-filled window, CFD study was carried out making reference to the experimental data to confirm the cellular flow of the liquid inside the window cavity. The mathematical models were developed, and then validated with the measured data. The excellent agreements between the experimental and numerical results illustrated the simulation models were reliable and can be used for further investigations in this study.

With the validated models, parametric studies were conducted to quantify the effects of glass pane type, liquid layer thickness, inlet temperature and flow rate of the flowing water through the heat exchanger on the performance of the liquid-filled double glazing, and the effects of the heat pipe ring, glass cover, inlet temperature and flow rate of the flowing water through the upper water box on the performance of the HPReAVCW under steady state. Then, the annual performances of the liquid-filled double glazing in nine different warm climates around the world, and the HPReAVCW in five different climates in China were investigated.

The integrative performance of eight water-filled double glazing and two glazed HPReAVCWs in a hypothetical single-storey farm building in Hong King was assessed. Three connection modes were compared firstly. With the optimal connection mode (all in series), the yearly energy-saving potential of the integrated system was assessed and the simple payback times of the water-filled double glazing and the glazed HPReAVCW were found as 3.6 and 4.9 years respectively. The numerical results illustrate that the two kinds of solar-absorbing facades have very good energy-saving potentials.