Sustainable Daylighting Retrofit of a Heritage Hotel Under Façade Preservation Constraints: A Climate-Based Simulation Study in Biskra, Algeria

Improving daylight performance in heritage hotels is essential for enhancing comfort, quality, and energy efficiency, especially in hot-desert climates where solar availability must be balanced with glare and overheating risks. However, façade preservation requirements limit conventional daylighting interventions, creating a need for climate-responsive and conservation-compatible solutions. This study investigates daylight optimization strategies for the Transatlantique Hotel in Biskra, Algeria, using Climate-Based Daylight Modelling (CBDM). The methodology combines three-dimensional modelling, in situ material characterization, and Radiance-based simulations with ClimateStudio version 2.3. Daylight performance was assessed using Spatial Daylight Autonomy (sDA), Annual Sunlight Exposure (ASE), Useful Daylight Illuminance (UDI), and Daylight Factor (DF). Tested scenarios included improved glazing transmittance, increased surface reflectance, and tubular daylighting devices (TDDs). Results show that the existing configuration provides insufficient daylight in guest rooms, with average illuminance in poorly performing rooms ranging from 140 to 310 lux. Material-based optimization increased Room 210's sDA from 3.9% to 62.3%, representing an approximately +1497% relative improvement, while UDI reached 58.6%. TDDs produced the strongest improvement: Room 110 sDA increased from 11.8% to 82.4% (+598%), while ASE decreased from 10.6% to 0.0%; Room 310 sDA increased from 31.2% to 100% (+221%), while ASE decreased from 16.9% to 0.0%. The novelty lies in integrating material-based and TDD strategies under strict façade-preservation constraints in a hot-desert heritage hotel.