A computational procedure that transforms transient radiant heat gains incident on zone-surrounding surfaces into a discrete time series of equivalent convective heat inputs to a lumped-zone thermal model, preserving the timing and integral effect of radiant exchange so the zone energy balance may be solved without explicitly resolving surface temperature dynamics.

Principle

Radiant exchanges that act on a zone's thermal balance can be represented as temporally distributed convective equivalents if the conversion preserves the net heat transfer and its time history relative to the zone's lumped heat capacity and time constants.

Demonstration

Illustrative scenario: An office receives variable solar irradiance through glazing across an hour. The RTS preprocess converts the surface-absorbed radiant flux into a sequence of convective-equivalent increments for each simulation time step. The lumped-zone solver then uses that convective series to update zone air temperature without solving additional surface heat-conduction nodes.

Misapplication

Treating RTS outputs as accurate representations of surface temperatures or using RTS in place of multi-node surface conduction models when thermal storage and surface temperature evolution materially affect occupant comfort or envelope heat flow; or applying RTS at time steps much shorter than the method's calibration without recalibration.

Consequence

Enables coupling radiant effects into simple (lumped) zone models with reduced computational cost and retained temporal fidelity of heat input; if misapplied it can underpredict or overpredict peak zone temperatures and dynamic storage effects.

Reversal

Fails or requires modification when surface heat storage, nonlinear radiative view-factor changes, strong spatial temperature gradients, or coupling with detailed façade thermal networks dominate the thermal response—there the explicit surface conduction and multi-node modeling are required.

Boundary

Clearly within: lumped single-node zone energy models where radiant gains are significant but surface temperature details are secondary. Boundary case: zones with moderate thermal mass and non-uniform surface exposures where RTS accuracy depends on calibration. Clearly outside: CFD-resolved spatial models, detailed multi-node wall/fenestration thermal networks, or problems requiring explicit surface temperature predictions.

Semantic Tension

Computational simplicity and reduced-model coupling versus the physical fidelity of surface-resolved transient heat transfer.

Synthesis

RTS is a pragmatic linearization that trades explicit surface resolution for a time-preserving convective representation of radiant gains; it is appropriate when zone-level energy accuracy and computational efficiency are the priority and when surface temperature dynamics are not decisive.