Two separate studies published in Scientific Reports examine passive and active solar technologies for improving building energy performance. The first study evaluates advanced glazing systems for cooling in hot-arid climates, while the second compares glazed and unglazed transpired solar collectors for air heating.
Study 1: Advanced Glazing for Cooling in Hot-Arid Climates
Overview and Methodology
A study evaluated advanced glazing technologies as a passive strategy to improve building energy efficiency in hot-arid climates. The research, conducted in Cairo, Egypt, combined experimental testing with simulation modeling to compare conventional and high-performance glazing systems.
Researchers tested four glazing types:
- Single-glazed clear glass
- Double-glazed clear glass
- Low-emissivity glazing (Vistalite sky-blue)
- Solar control glazing (Stopray Smart 30)
Experimental measurements were taken using small concrete and brick chambers equipped with temperature sensors. The TRNSYS 17 software was used for simulation, which was validated against experimental data and then applied to a seven-story office building case study.
Key Findings
Single-glazed clear glass resulted in indoor temperatures up to 58°C, double glazing up to 48°C, low-emissivity glazing up to 45°C, and solar control glazing up to 41°C.
- Annual Simulation: Solar control glazing maintained peak indoor temperatures around 33°C, compared to 45°C for conventional double glazing, representing a 22% improvement.
- Cooling Energy Consumption: During peak summer months, cooling energy consumption decreased from 2650 kWh (conventional) to 1200 kWh (solar control glazing), a reduction of over 50%.
- Carbon Emissions: Over a two-month period, carbon emissions reduced from 1325 kg CO2 to 600 kg, a 54.7% decrease.
Conclusions
The authors concluded that solar control glazing is effective for large office buildings in hot climates, reducing cooling loads and carbon emissions. The validated simulation model may support future design optimization.
Study 2: Comparison of Glazed and Unglazed Transpired Solar Collectors
Overview and Methodology
A separate study compared the performance of glazed and unglazed transpired solar collectors (TSCs) for building-integrated solar air heating. The research was conducted at Al-Zaytoonah University in Jordan from January to March 2025 under clear-sky conditions with low wind.
Both collectors featured identical galvanized steel absorber plates (3×2 meters, 22,400 perforations). The glazed version included a 4 mm low-iron glass cover positioned 30 mm from the absorber. Performance was assessed across varying airflow rates and solar irradiance levels, measuring thermal and exergy efficiencies, heat exchange effectiveness, ventilation load reduction, and wall heat-loss recapture index.
Key Findings
The glazed collector achieved 48–75% thermal efficiency, while the unglazed collector achieved 42–65%.
- Heat Exchange Effectiveness: The unglazed collector was slightly higher due to direct air contact.
- Wall Heat-Loss Recapture Index (unglazed): 93% at low irradiance, exceeding 60% at high irradiance.
- Ventilation Load Reduction (glazed): 60–90% with increasing irradiance; outlet temperature increased by up to 22°C.
- Economic Analysis: The unglazed collector had a payback period of approximately 4.4 years, compared to approximately 5.2 years for the glazed collector. The glazed collector provided higher annual energy savings and carbon emission reductions.
Conclusions
The authors stated that the choice between glazed and unglazed TSCs depends on project requirements. Unglazed collectors are lower cost with strong dynamic insulation performance, making them suitable for retrofits. Glazed collectors offer higher efficiency and better ventilation preheating, making them appropriate for high-performance buildings. The study's 1-D heat-transfer model was validated against measurements and used for annual projections.