Stationary Heat Transfer in an Active Building Thermal Protection Envelope Equipped with Tubular Heat Transfer Devices

An active thermal protection envelope (ATPE) is a new kind of systems for maintaining temperature conditions in buildings and structures, which emerged after the “warm floor” and “warm walls” systems. The article substantiates the relevance of studying the thermal characteristics and practical application of an ATPE comprising tubular heat transfer devices (THTDs). A 1D analytical solution and a 2D numerical solution of the heat transfer problem in an ATPE are developed. For the 2D solution, a numerical scheme that takes into account conjugate heat transfer between the heat distribution layer (HDL) and thermal insulating layer (TIL), as well as the modeling procedure, are presented. For verifying the results, numerical and analytical calculations were carried out, and the temperature distributions in the heat distribution layer for one of the ATPE versions were compared. The 1D analytical solution is in good agreement with the 2D numerical calculation results. The temperature differences arising in the HDL and at its surface, as well as the THTD temperature overheating are determined. A tubular heat transfer device overheating calculation method for carrying out practical computations is proposed. The Biot number value at which the standardized temperature distribution parameters at the thermal protection structure inner surface are achieved is estimated. A conclusion is drawn that, owing the use of an ATPE equipped with tubular heat transfer devices, the heat carrier temperature can be approached closest to the indoor temperature. This means that the heat supply systems of buildings and structures can be made more efficient in exergetic and energy respects at the expense of insignificantly larger heat losses, especially in the case of using low-grade heat sources, and also during heat transformation and storage. Formulas for calculating the THTD placement pitch, minimal HDL temperature, and THTD specific power are presented.