# Experimental Characterization of Thermal Conductivity with a New Compact Hot-Box Prototype
## 1 Introduction  
In the energy transition, buildings are considered a low-carbon-emission energy system. In the current context, residential and commercial buildings are responsible for consuming one third of the electricity produced globally and generating 17% of the emissions [1]. Based on these characteristics, buildings represent a key target for improving energy efficiency, environmental sustainability, construction phases, and financial viability. Buildings are, therefore, undergoing a process of adaptation to meet the urgent need for efficient and sustainable building systems, seeking a balance between environmental and financial considerations. This necessity has driven the construction industry, research institutes, and universities to explore alternatives for optimizing the energy performance of buildings in an environmentally friendly and efficient manner. Thermal performance is fundamental to meet the new standard requirements in building energy. Therefore, the thermal characteristics of each component of the building envelope must be studied from energy and environmental points of view. The materials used in the building envelope and interior are directly correlated with energy efficiency, indoor thermal comfort, lifecycle performance, and financial balance. Thus, the mechanical, thermal, and acoustic properties of the materials used play a fundamental role in developing construction solutions. In this regard, measuring these parametersensures a better understanding of how materials influence the energy efficiency of construction systems. In the current scenario, the integration of new materials derived from agricultural [2; 3; 4] and industrial [5] waste is becoming increasingly popular in construction systems. These new materials are used to make insulation panels and fiber-reinforced composites for cement and bricks. Insulation panels based on various recycled agricultural waste provide alternative construction materials using low technology compared to traditional insulation. The Dominican Republic is in the Caribbean Sea and has a tropical climate [6]. Agriculture is a key sector of the economy, which generates a large amount of agricultural waste, particularly rice husks, sugarcane bagasse, coconut fiber, beans, and cocoa shells. The production of insulation panels from these residues and their integration into the local construction system contributes to reducing the environmental impact, revaluing these materials, and minimizing costs. In that sense, the characterization of thermal properties is crucial for the appropriate use of insolation panels. Thermal conductivity is a fundamental parameter for calculating the thermal transmittance of construction materials, thus providing a benchmark that helps classify the insulation level of a material. Currently, different instrumental methods exist for measuring thermal conductivity, which can be classified into two main categories: steady-state and transient measurement techniques [7]. Steady-state techniques include hot-box methods (HBMs) and heat-flow meters (HFMs), while transient techniques are associated with hot wire and hot disks. However, in developing countries, the use of commercial techniques is almost prohibited. Consequently, there is an urgent need to develop alternative methods for measuring thermal conductivity that are more flexible, accessible, and less expensive than the currently available methods, even in a prelaminar fashion [8]. In general, commercial equipment that is used to measure thermal conductivity has prohibitive costs (for example, equipment such as hot disk instruments), limiting or preventing its availability in developing countries. In the case of the hot-box method, the ISO 8990:1994 [9] and ASTM-C518 [10] standards focus on characterizing thermal transmittance for construction material using the hot-box methodology, which is classified into two types based on experimental techniques: a guarded hot box and a calibrated hot-box.