Design of vacuum thermal insulation fitting in solar heating applications

Abstract

The presented paper deals with designs of the vacuum thermal insulation fitting in solar heating applications. Fitting designs, identified by the  authors of this paper, reflects the construction problem of a flat vacuum solar collector caused by the conduction of heat gained with solar  collectors to the collector casing through thermal conductive connection located across the interface between casing and outer piping. As this heat further leaks into the surrounding environment, heat losses of the solar collector is higher and therefore thermal performance of the whole solar system is reduced. The solar collector element in the form of a vacuum  thermal insulation fitting allows a connection of the solar collector with  outer hydraulic circuit of the solar system without creating thermal  bridges while ensuring vacuum tightness of the collector casing. A part in the evaluation process of the proposed design was a vacuum thermal  insulation fitting modelled in CAD environment followed by heat transfer analysis under several operation scenarios (normal operation, extreme  operation, etc.). Subsequently, a functional prototype was manufactured for measurements and verifications of the desired characteristics of  fitting under different operating conditions. All the results of  measurements and simulations demonstrated not only the ability of fitting to ensure vacuum tightness of the solar collector but also the ability of reducing overheating of the collector casing as well.