A computationally lightweight thermal simulation framework based on explicit CTF formulation for annual energy estimation

High-accuracy building simulation tools such as EnergyPlus are costly for large-scale parametric studies. This paper presents a lightweight, calibration-free thermal simulation framework based on an explicit Conduction Transfer Function (CTF) formulation. It is verified against EnergyPlus across 24 scenarios (four Brazilian climates, six envelope configurations) along three axes: parametric ranking, load magnitude, and temporal pattern. The framework preserves the dominant-load ranking exactly in the cooling-dominated climates (Spearman ρ=1.00) and strongly in the heating-dominated climates (ρ=0.94), completing each annual run in tens of milliseconds. Magnitude is over-predicted where cooling governs (pooled NMBE +25.2%) but essentially unbiased where heating governs (+2.1%), meeting the bias criterion of ASHRAE Guideline 14 but not its dispersion criterion. An annual heat-balance decomposition that closes to 0.04% locates the excess in the surface pathways. It is therefore positioned as a fast envelope-screening and ranking tool for early-stage design, not a calibrated predictor of absolute consumption.