Thermal and Optical Properties of the Sunspace Casing as Factors Influencing Temperature Rise in Greenhouse Systems

In sunspaces, there is an observable temperature rise above the external air temperature, caused by solar gains and the buffering effect of their enclosure. In addition, their external partitions form a barrier preventing the direct influence of the external environment and delaying the natural deterioration of elevation surface. In the paper, the temperature rise in a glazed balcony attached to a typical flat in a multifamily building, together with the energy demand in the living zone, were assessed with the use of dynamic computer simulations. Ten variants of the sunspace casing were analysed, with different thermal and solar energy transmittance of the glazing (which is a novel subject in the research area). This enabled us to evaluate average values of the temperature reduction factor during the year and to choose the most efficient variant of the sunspace external partitions. It turned out to be an insulated, double-glazed casing with a spectrally selective coating (type O 21), combining high insulative properties with high solar transmittance. These features allowed the temperature in the sunspace to rise by almost 10°C (compared with the external air) and lower total energy demand in the flat by 33% (compared with a flat with an open balcony).

Performance Augmentation of the Flat Plate Solar Thermal Collector: A Review

The need for hot water in residential buildings requires a significant energy potential. Therefore, an efficient water heating system is important to achieve the goal of saving high-grade energy. The most simple and cheapest solar water heater is a flat plate solar collector (FPSC), which can increase the thermal energy of fluid by absorbing solar radiation. The performance of FPSC is comparatively low due to the dilute nature of solar insolation. Therefore, advancement of FPSC is being undertaken to improve the performance and achieve size reduction. In past, several techniques have been exploited to improve the performance of FPSC, which are presented in the present paper. These techniques include surface modifications, use of nanofluids, solar selective coating, and applications of a mini/macro channel, heat pipe, and vacuum around absorber. Surface modification on the absorber/absorber tube techniques are exploited to transfer the maximum possible solar energy to working fluids by increasing the heat transfer rate. Insertion of wire mesh, coil, and twisted tapes in the flow has great potential to increase the Nusselt number by 460% at the expense of a large pressure drop. Selective coating of Cu0.44 Ti0.44 Mn0.84 helps to absorb up to 97.4% of the incident solar energy, which is more significant. Many nanofluids have been exploited as heat transfer fluids, as they not only increase the performance but also reduce the fluid inventory. So, these techniques play a very prominent role in the performance of FPSC, which are discussed in detail. Summaries of the results are presented and recommendations proposed.