Experimental and Numerical Study on the Heat Transfer Characteristics of a Newly-Developed Solar Active Thermal Insulation System

Abstract

A newly-developed solar active thermal insulation system (SATIS) is introduced with the main objective to accomplish a highly-dependent total solar transmittance on the irradiation angle. SATIS is also designed to obtain the maximum transmittance at a prescribed design irradiation angle and to reduce it remarkably at higher irradiation angles. A purely mineral thermal insulation plaster with micro hollow glass spheres is applied to manufacture the investigated SATIS prototype. Light-conducting elements (LCEs) have been introduced into SATIS and suitable closing elements have been applied. The SATIS prototype has been investigated both experimentally and numerically. It turned out that the contributions of conduction, radiation and convection to the effective thermal conductivity of SATIS, without the closing elements (49 mWmK), amount to 86.2%, 13.2% and 0.6%, respectively. The angle-dependent short-wave radiation exchange within the LCE has been investigated via ray tracing. At the incidence angle of 19% (design angle), 27% of the radiation within the LCE is absorbed by the absorber plate, resulting in measured and computed total solar energy transmittances of 11.2%/11.7%, respectively. For a typical summer irradiation angle of 60%, 98% of the incident radiation is absorbed by the surfaces at the entrance of the LCE. The corresponding total solar energy transmittance amounts to 2.9%.

Assessment of the Annual Transmission Heat Loss Reduction of a Refurbished Existing Building with an Advanced Solar Selective Thermal Insulation System

“…The obtained highly solar irradiation angle-dependent transmittance of SATIS [17] is associated, however, with an increase in the effective thermal conductivity of the insulation layer compared to the basic insulation material without SATIS (57 mW m K vs. 45 mW m K ). This would imply an increase in the transmission heat loss, which may counterbalance the solar gain achieved by the introduced SATIS concept.…”

“…The axis of the stepped hole of the LCE is inclined at an angle of 19°t o the horizontal, so that solar gains can be obtained preferably in winter months. For solar radiation incident at this angle, the highest total solar energy transmittance could be determined both experimentally (11.2%) and numerically (11.7%) [17].…”

“…The steady state model of SATIS, which was developed with COMSOL Multiphysics ® and thoroughly validated and described in [17], is shown in Figure 1a,b in side and isometric view, respectively. The model consists of a single light conducting element (LCE).…”

“…The prototype of the recently published solar selective thermal insulation system (SATIS) [17], which consists of a thermal insulation plaster with micro hollow glass spheres as the base material and incorporated light conducting elements (LCEs), showed a highly angle-dependent total solar energy transmittance in experiments. At the design angle of SATIS (19°), the experimentally determined g amounts to 11.2% and is reduced by 75% to 2.9% at an incidence angle of 60°.…”

“…The objective of this work is to make use of the very well validated steady state SATIS model from [17] to carry out the required design review aiming at enhancing both the insulation (λ eff ) and solar gain (g) characteristics of SATIS. After defining the influencing parameters on both characteristic values (λ eff and g), a numerical parametric study is carried out to explore the respective influence of each design parameter on each characteristic value of SATIS.…”