Heat Transfer Performance and On–Off Thermal Response of a Building Wall Embedded with a Reversible Loop Heat Pipe

Building on a previously developed valve-controlled reversible loop heat pipe (RLHP) and the corresponding RLHP-embedded wall, component- and wall-scale experiments were conducted. The heat-transfer performance of the RLHP was evaluated at filling ratios of 10–70% and heating powers of 25–400 W, and its forward and reverse operation was evaluated at the component scale using a filling ratio of 50%. The on–off dynamic responses of the RLHP-embedded wall and a reference wall were subsequently compared under heating powers of 20–200 W. The results showed that filling ratios ranging from 40% to 70% provided a relatively effective operating range under the tested conditions. Among the tested filling ratios, 50% exhibited the lowest and most stable apparent equivalent thermal resistance, with an average value of approximately 0.039 m2·K/W. At 400 W, the quasi-steady average temperature differences during forward and reverse operation were 17.2 °C and 16.9 °C, respectively. At 200 W, the first-hour temperature rise on the unheated side was approximately 6 °C for the RLHP-embedded wall, compared with 1.2 °C for the reference wall. During the combined heating-off–valve-closed stage, the heat-retention duration increased with the preceding heating power.