Abstract
Photovoltaic-thermal (PVT) solar collectors generate heat and electricity. Building Integrated (BI) façade collectors are suited to high rise buildings. Ulster University researches novel Integrated Collector-Storage Solar Water Heaters (ICSSWH). This study investigates Planar Liquid-Vapour Thermal Diode (PLVTD) heat transfer and characterises performance of a BIPVT-PLVTD-ICSSWH prototype.A thermal resistance network representing evaporation, vapour transfer, condensation, fluid conduction and convection, plate-to-plate radiation, and solid conduction is established and evaluated using Stefan-Boltzmann and Fourier laws together with Rayleigh/Reynolds-Nusselt and Rohsenow correlations. A novel method is proposed for evaluating pressure driven vapour transfer thermal resistances. Heat transfer through a small (300x500mm) PLVTD was measured under various conditions (5-75°C and 50-2000 W/m-2). Conductances were 50<U12f<1300 W·m 2K 1 in forward mode and 8<U12r<24 W·m-2K-1 in reverse, consistent with predictions.
A lumped parameter PVT-PLVTD-ICS model of Hottel-Whillier-Bliss form considers optical, thermal and electrical energy balances during collection and heat retention periods. Calculations for single glazed collectors demonstrate benefits of thermal diodes. A prototype stainless-steel PVT-PLVTD-ICS collector with 700x1400mm absorber, flat 100L water tank, and optimized PLVTD (70mm deep, supported internally by a strut array) was fabricated. Absorber-evaporator plate was painted black and 120 quartered monocrystalline cells were encapsulated and bonded on using clear silicone resin. Series-parallel cell interconnections produced ~19V and >0.5A to drive the centrifugally pumped evaporator wetter. Transparent Perspex and 150mm polystyrene were used for insulation. Multi-day solar simulator tests (370, 610 and 870 W/m 2 irradiance) were undertaken. Ambient temperatures were 25±6°C during 6-hour collection periods and 21±5°C during 18-hour retention periods. Achieved thermal and photovoltaic collection efficiencies were ~40% and ~6% respectively at 0.06 m2K·W-1. Overnight heat retention was 71±2% efficient with 0.85±0.04 W·m 2K 1 overall loss coefficient. Reverse mode diode conductance was 1.7±0.5 W·m 2K 1. Thermal camera images highlight evaporator dry spots which cause lower than expected forward mode diode conductance (10<U12f<100 W·m 2K 1). Poor PV efficiency was primarily due to cell damage during fabrication.
The work demonstrates that BIPVT, PLVTD and ICSSWH can be successfully combined in a flat form. Design improvements are suggested and recommendations for further research are given.
| Date of Award | Jul 2017 |
|---|---|
| Original language | English |
| Supervisor | Aggelos Zacharopoulos (Supervisor), Mervyn Smyth (Supervisor) & Jayanta Mondol (Supervisor) |
Keywords
- thermal diode
- photovoltaic-thermal
- phase change heat transfer
- solar water heater
- PV/T
- building integrated
- BIPV
- BIPVT
- BISTS
Cite this
- Standard