A climate-adaptive opaque building envelope can significantly reduce heating and cooling energy use while improving the indoor thermal comfort. However, insufficient computational modeling and simulation techniques in modern building energy modeling tools are critical barriers to expedite the development of this emerging building technology. This paper explores an alternate modeling technique to model an opaque climate-adaptive building envelope with Modelica. As a case study, an integrated, climate-adaptive structural building energy module that consists of a double-sided hydronic heating and cooling layer embedded in a composite structural insulated panel is introduced. This paper describes energy saving potentials of the proposed systems and discusses the benefits that Modelica offers for the development of climate-adaptive building envelopes.