The heat transfer coefficient (HTC) is critical in building energy simulation, governing the rate of heat exchange in indoor and outdoor surfaces. Earlier studies often assumed a constant indoor surface HTC, which can misrepresent actual thermal loads in underground buildings (UBs). This study numerically investigates heat transfer in a real-size un-conditioned UB with surrounding soil medium, emphasizing the spatiotemporal variation of indoor surface convective HTC. Three-dimensional largeeddy simulation (LES) combined with WALE sub-grid scale model and Boussinesq approximation was used for solving coupled energy and flow equations at four representative soil steady-states over an annual cycle. Results reveal relatively uniform spatial distribution of convective HTC across indoor surfaces but noticeable temporal fluctuations driven by seasonal changes in soil temperature. Depending on the indoor air movement, natural convection or stagnant air, the convective HTC can vary from 1.8 W/m2K to 0.03 W/m2K. The findings demonstrate that dynamic HTC is more necessary compared to surface-specific HTC values for accurate thermal load estimation in UBs.

Chiller-Water-Side Economizer (WSE) plants are widely adopted in data centers and commercial buildings because they leverage ambient wet-bulb conditions to provide free cooling, offering significant savings compared to chiller-only operation. However, current practice lacks systematic evaluation; design engineers select critical operational sequences (like tower priority versus chiller priority) primarily based on experience. No comprehensive study compares these sequences across multiple ASHRAE climate conditions to provide a consistent guideline for selecting an appropriate sequence as a starting point. To address this research gap, this work proposes developing wet-bulb temperature based performance maps as a decision-support. We utilize a high-fidelity co-simulation environment, modeling the Chiller-WSE plant architecture using Modelica models (encapsulating thermodynamics and control logic) exported as Functional Mock-up Units (FMUs). The methodology involves a cross-climate evaluation across representative ASHRAE climate zones for two sequences: chiller-priority (chillers engage first) and tower-priority (cooling tower maximized for cold water inlet).

Simulation outputs capture total HVAC energy consumption (kWh), which is aggregated into designer-ready performance maps that delineate sequence decision boundaries. The results, plotted for climate zones 1A to 4C, show clear distinctions for the optimal control sequence. Specifically, we observed different operational zones of distinction in the range of -4°C to 11°C where tower priority and 11°C to 17°C chiller priority sequence can save energy compared to the other. This case study provides designers with data-driven tools, demonstrating the energy-saving potential achieved through the systematic selection of the optimal control sequence.

This study presents a self-powered dynamic façade integrating thermoelectric generators (TEGs) with phase change materials (PCMs) to convert temperature gradients into electricity for automated shading. A prototype with two 40 mm × 40 mm TEGs and a 29 °C PCM was tested in a solar chamber and outdoors. Solar chamber experiments charged a 1.5 V supercapacitor to 1.0 V, which intermittently powered a DC motor to rotate an aluminum louver. Optical–thermal enhancement using a Fresnel lens and acrylic dome improved voltage output by 20%, demonstrating a scalable pathway toward autonomous façade operation and reduced building energy demand.

The increasing intensity and frequency of extreme weather events driven by climate change underscore the urgent need for design and retrofit strategies that enhance both the energy efficiency and thermal resilience of buildings. Among these strategies, cool building envelope materials have demonstrated effectiveness in mitigating indoor overheating and reducing urban heat island effects. While numerous studies have documented the summer performance benefits of reflective materials, their seasonal trade-offs remain less understood. This study investigates the dual impact of cool building materials on energy performance and thermal behavior across summer and winter periods, evaluating how increased surface reflectivity can enhance cooling efficiency and thermal resilience in warm conditions without compromising wintertime performance.

The growing need for smart, energy-efficient, and occupant-centric buildings has created a demand for advanced control systems that can optimize building operations to balance energy savings, demand flexibility, and comfort. However, current building energy simulation tools, such as EnergyPlus, have limitations that hinder the development and evaluation of these complex control systems. To address this challenge, we introduce a high-fidelity building emulator that dynamically couples EnergyPlus with Radiance for enhanced daylight modeling. The introduced workflow allows researchers and practitioners to rapidly develop and evaluate innovative control solutions. An example study looking at a south-facing office zone revealed up to 67% deviation in predicted light levels, which can significantly impact building assessment.