Optimization and application potential of liquid flow window

Abstract

This study focuses on the optimization and application potential assessment of liquid flow window. Liquid flow window is a multi-glazing system with a liquid flow in the glazing cavity, which is connected to a double pipe heat exchanger via insulated tubing; all together form a complete closed circuit. At the heat exchanger, the liquid from window releases bsorbed solar heat to the cold feed water. Liquid flow in the window cavity is driven by buoyance force and this system contributes to building energy saving from two aspects: the eduction in room heat gain and the cold feed water preheating of a domestic hot water system. Nevertheless, the thermal extraction at window may slightly raise the winter space heat loss. This study was conducted with both experimental and numerical analysis. System optimization was done in the first place based on a conceptual design of the liquid flow window system. Influence of the window geometry on the system performance was evaluated with a self-developed FORTRAN program. The flow characteristics of the liquid layer in the cavity with different header designs were compared using CFD analysis. A prototype used for experimental measurement was constructed primarily based on the results of system optimization. The experiment was carried out in Changzhou, Jiangsu province from late September to early October 2014. Two different working fluids were adopted in the experiment, namely pure water and anti-freezing liquid. The anti-freezing liquid used was aqueous solution of propylene glycol, which has a lower freezing point than water. Consecutive days measured data were recorded and analyzed, and subsequently used for simulation in model validation. The model validation exercises were conducted via two different approaches: firstly the self-developed FORTRAN program and later on, the public-domain ESP-r building simulation program. Good agreement between the measured data and the FORTRAN simulation results made it possible to carry out year-round performance prediction in different climate zones. Performance optimization considering different hot water demand profiles of office and residential buildings was carried out subsequently. Phase Change Material was added to the heat exchanger to achieve the goal of thermal energy storage and load shifting. The PCM-incorporated mathematical model was built, and the developed FORTRAN code was found in good quality by results comparison with published data. Building energy simulation was executed using the model successfully validated via the ESP-r program. Year-round performances were predicted accordingly, taking either water or anti-freezing liquid as the working fluid where appropriate. Lastly, Life Cycle Assessment (LCA) was carried out to determine the Cost Payback Time (CPBT), the Energy Payback Time (EPBT) and the Green-house Gas Payback Time (GPBT). The application potential of liquid flow window is found promising with even shorter EPBT and GPBT than the economic payback time.

Date of Award	2 Oct 2015
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Tin Tai CHOW (Supervisor)