Evaluation of a Peak Cooling Load Estimation Model for Radiant Systems in Large Indoor Spaces: Validation with BES and Energy Saving Analysis

Accurate estimation of peak cooling load is essential for system sizing and early-stage design of Radiant Panel Heating-Cooling Systems (RPHCS) in large indoor spaces (LIS). Conventional peak-load procedures generally assume fully mixed indoor air conditions and uniform envelope-driven heat transfer. However, under radiant cooling, stratified thermal environments commonly form due to limited air motion and buoyancy effects, resulting in potential overestimation when using traditional calculation approaches. To address this gap, a simplified method for estimating peak cooling load based on occupied zone conditioning logic has been proposed. The method introduces a two-zone thermal representation, revised longwave radiation treatment from upper envelope surfaces, and a modified envelope load framework tailored to stratified indoor thermal structures. To evaluate the validity of the simplified model, a representative LIS equipped with RPHCS was selected as a case study. Both the proposed simplified method and a previously validated unsteady Building Energy Simulation (BES) were applied under identical boundary conditions. Peak total loads, load composition, and envelope contributions were compared between the two approaches. Results show that the simplified method produces a conservative yet reasonable prediction, corresponding to approximately 99.6% to 118.7% of the 5% exceedance peak derived from the detailed simulation. The error range is consistent with engineering design safety margins while avoiding excessive oversizing. In addition, the energy-saving potential of conditioning only the occupied zone was investigated using the detailed simulation model. The analysis indicates that adopting occupied zone cooling can reduce peak cooling capacity requirements by approximately 24.3%, primarily due to reductions in sensible envelope heat transfer. The findings demonstrate that the proposed method is suitable for conceptual design stages where rapid, reliable peak load estimation is required, offering an effective balance between computational efficiency and prediction accuracy for radiant systems in large indoor spaces.