Energy Performance Analysis of Photothermal Building Windows
Open Access
- Author:
- Duan, Qiuhua
- Graduate Program:
- Architectural Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- July 01, 2021
- Committee Members:
- Ali Memari, Major Field Member
Somayeh Asadi, Major Field Member
Julian Wang, Chair & Dissertation Advisor
John Mauro, Outside Unit & Field Member
Sez Atamturktur, Program Head/Chair - Keywords:
- building windows
solar infrared radiation
thermodynamics
condensation
low-e coating
energy performance - Abstract:
- Research over several decades has shown that the thermal and optical performance of windows significantly influences building energy consumption. In general, 30∼40% of current building windows are single-pane, and they are responsible for over 50% of the total energy loss in the United States. To improve the performance of single-pane building windows, adding low emissivity (low-e) coating on existing windowpanes is one of the main practical retrofitting strategies. The low-e coated windows can not only reduce radiative heat transfer by reflecting solar radiation to the exterior in summer but also lower heating needs in winter by keeping the heat from radiating to the outside. Consequently, adding low-e coatings or window films may decrease energy consumption. However, the low-e coating may reflect about 50% solar near-infrared (NIR) to outdoor, which may offset the solar heat gain benefits for indoor heating energy savings in winter. Furthermore, in winter, the low-e coated windowpane is colder than the windowpane without low-e coatings, and sometimes it is nearly as low as the outside temperature. In other words, the condensation risk of the window’s internal surface will be increased because of the low absorptance of windowpanes resulted from adding low-e coatings. To address these two engineering problems about heat loss in winter, a nanoscale photothermal effect-based coating has been developed and incorporated into the glazing system, which may independently modulate the NIR and then increase the windowpane temperature, so that it can greatly reduce the heat loss between the interior to the windows and also improve the condensation resistance of windows. The primary goal of this study is to establish and examine the methods of simulating and analyzing the energy performance of the photothermal windows. This study first builds a new spectral conversion model that can decompose hourly broadband global horizontal and direct normal solar radiations to the visible and infrared components, which is necessary for analyzing the proposed photothermal windows because of their spectral selectivity. Subsequently, the optical and thermal properties of the photothermal films on single-pane windows are obtained from lab measurements under solar simulators, and then the photothermal window characteristics and the above-derived near-infrared solar radiation will be combined into the development of a new analytical model incorporating nanoscale photothermal effects. Based on this new analytical model, I am able to determine the window temperature changes upon the photothermal effect activated by the solar infrared radiation and yield dynamic solar heat gain coefficients. Then, a parametric energy simulation method is proposed and investigated for the energy performance of building windows, taking both condensation and photothermal effects into account, relative to the conventional low-e coated single-pane window. This research paves an underlying energy-saving mechanism for understanding the nanoscale photothermal phenomenon at the architectural scale. In addition, the developed solar spectral model can be applied to the existing weather files and decompose broadband solar radiation data into narrowband ones for analyzing the energy performance of spectrally selective glazing or other elements of building envelopes. From the implementation perspective, the designed photothermal film can be added to the existing single-pane windows for energy-efficient retrofitting purposes.