Comprehensive thermal performances study on fin-enhanced thermo-activated building envelopes with anisotropic heat injection capacity

Abstract

The thermo-activated building envelopes (TABEs) possess special structural and energy features, providing a unique opportunity for the energy-efficiency measures of non-transparent building envelopes to shift towards low-carbon properties. To address the long-standing issue of heat charging efficiency that has plagued conventional TABEs (ConTABEs), fin-enhanced TABE (FinTABE) with anisotropic charging capacity is proposed. The dynamic thermal behaviors and charging performances of FinTABEs are numerically studied with a validated model, and then the effects of fin materials, fin heights, fin thicknesses, fin numbers, installation directions, pipe spacings, and insulation thicknesses are investigated. Results indicate that the directional heat injection measures can effectively improve the performances of opaque envelopes. Compared with ConTABEs, the further improvement in daily room heat loss of FinTABEs under different charging conditions is 0.73 % to 52.92 %, while the maximum increase of daily total heat loss does not exceed 3.5 %. Besides, the performance enhancement in FinTABEs will gradually reach the upper limit when the vertical fins’ thermal diffusion capacity exceeds that of brass/aluminum, the characteristic height reaches 0.6, or the fin thickness reaches 1.5 mm. Results also indicate that the vertical fins can significantly expand the heat accumulation area inside FinTABEs and change the circular heat accumulation shape into ellipse shapes. Differently, the horizontal fins are conducive to increasing the horizontal size of the heat accumulation area, but further installing fins in the horizontal direction has a slight effect on increasing the vertical height of the heat accumulation area. In addition, the directional heat injection design can effectively suppress the shrinkage of the heat accumulation area when the insulation thickness is reduced, and the insulation material can be reduced by more than 40 % while maintaining similar performances as standard ConTABE.