# Growing Kratky Basil in Trombe Wall Cavity: Energy Performance
### Research Background  
#### 1.2.1 Origin and Evolution of Trombe Walls  
The utilization of passive solar-capturing devices, such as windows (enhanced by the advent of glass), dates back centuries. However, the Trombe wall, as a specific architectural feature, emerged during the Industrial Revolution. The concept of a glass-covered air heater is attributed to [PERSON], who patented the design in 1881 [11]. Despite its potential, the idea did not gain widespread traction until the mid-20 th century, when it was further developed and popularized by the French engineer [PERSON]. [PERSON] secured patents for the design in 1956 and 1971 [12; 13] and implemented the concept in buildings located in mountainous regions of France during the 1960s and 1970s. His collaborative research with [PERSON] laid the groundwork for understanding the system's performance.  
Interest in Trombe walls expanded in the 1970s and 1980s, driven by energy crises and rising environmental concerns. Notable studies from this period include research conducted by the National Renewable Energy Laboratory (NREL), which provided quantifications and optimizations, and foundational work by [PERSON] and [PERSON] [14; 15]. Additionally, practical implementations by French architects [PERSON] and [PERSON] contributed to their adoption in residential architecture [16].  
By the late 20 th century, research had focused on refining Trombe wall parameters, including optimal dimensions, thermal mass, glazing options, air gap sizes, and ventilation systems [5; 6; 17; 18; 19; 20]. Studies also explored their adaptability to diverse climates and building orientations [21; 22; 23; 24]. Recent advancements have introduced innovative materials  
Figure 1: The Trombe wall in its original state (**A**) and after retrofitting (**B**,**C**). Pictures taken on 9 February 2022, 13 July 2022, and 11 October 2022, respectively.  
and designs, summarized in meta-analyses by [PERSON] and [PERSON] [3; 25]. The development of energy simulation software has further enhanced performance assessments, enabling detailed studies of unique configurations worldwide [26; 27; 28; 29; 30].  
One prominent research focus is the substitution of traditional heavy thermal masses with phase-change materials (PCMs). These materials can be paraffin waves, fatty acids, salt solutions, or other specific substances capable of storing heat through state changes (e.g., solid to liquid), offering significant weight and space advantages over conventional Trombe walls. Studies by [PERSON] and others have demonstrated the potential of PCMs to modernize and expand Trombe wall applications [31; 32; 33; 34; 35].  
Another emerging trend is integrating Trombe walls with additional functionalities. The warm, dry air gap between the wall and glazing can accommodate complementary solar technologies like photovoltaics [36; 37; 38], solar panels [22], and geothermal heat exchangers [39]. Notably, this last study combined Trombe walls with a hydroponic system, using heated air to regulate temperatures in a nearby greenhouse, showcasing the potential for its combined use.  
Trombe walls are widely recognized as efficient, versatile solutions for heating and cooling, comparable to other sustainable technologies like photovoltaics and green walls [32; 40; 41]. However, adoption remains limited due to design challenges, particularly aesthetic concerns, which hinder their popularity among architects and designers [3].