Construction and Calibration of a Unique Hot Box Apparatus

Abstract

A variety of mathematical models are available to estimate the thermal performance of buildings. Nevertheless, mathematical models predict the thermal performance of buildings that might differ from the actual performance. The hot box is a widely-used test apparatus to assess the actual thermal performance of various building envelope components (walls, roofs, windows) in the laboratory. This paper presents the process of designing, constructing, and calibrating a unique small-scale hot box apparatus. Despite its smaller metering area (1.0 m × 1.0 m), this apparatus met the key requirements (below ±0.25 °C fluctuations in chambers’ air temperature, and below 2.0% variation from the point-to-point temperature in reference to the temperature difference across the specimen) as prescribed in the ASTM C1363 and ISO 8990 standards. The walls of this apparatus are uniquely constructed using vacuum insulation panels or VIPs. The efficient and novel use of VIPs and workmanship during the construction of the apparatus are demonstrated through the temperature stability within the chambers. The achieved range of temperature steadiness below ±0.05 °C and point-to-point temperature variation below 1.0% of the temperature difference across the specimen allow for this apparatus to be considered unique among the calibrated hot box categories reported in the literature. In addition, having an affordable, simple-to-operate, and high-accuracy facility offers a great opportunity for researchers and practitioners to investigate new ideas and solutions. The apparatus was calibrated using two extruded polystyrene foam (XPS) specimens with thicknesses of 2″ and 4″. The calibration exercise indicates small differences between results obtained numerically, theoretically, and experimentally (below 3.0%). Ultimately, the apparatus was employed to measure the thermal properties of a specimen representing a lightweight steel framing (LSF) wall system, which is commonly used in cold climates. The results obtained experimentally were then compared to the ones estimated numerically using a 3D finite element modelling tool. The difference between the results obtained by both methods was below 9.0%.

Innovative Environmental Chamber Construction for Accurate Thermal Performance Evaluation of Building Envelopes in Varied Climates

“…In the case of one-dimensional heat flow, the most common methods used to measure the thermal properties are the guarded hot plate [10] and the heat flow meter [11]. However, using these methods has some limitations, as they are only capable of testing homogeneous building materials such as concrete, plywood, brick, and glass [12]. In the case of large-scale and nonhomogeneous building envelopes, environmental chambers are used to determine the thermal properties of different building components at controlled environmental conditions (see ASTM C1363 [8]).…”

The Experimental Calibration of a Two-Storey Guarded Hot Box Test Apparatus

“…To capitalize on this opportunity and reduce the carbon footprint in this sector, building codes are rapidly evolving to add increased energy efficiency measures for newly built and retrofitted buildings. As a result, this has increased the level of interest in accurately measuring the thermal performance of building envelope assemblies using novel and sustainable building materials and construction techniques [11]. Before widespread implementation in the construction field, it is critical that new innovative solutions be thoroughly researched and tested.…”

“…[12]. Predicting the thermal performance of building envelopes requires knowledge of both the thermal characteristics of its individual materials and the overall thermal characteristics of these materials when combined into an assembly [11].…”

“…Buratti et al [15], Sassine [16], and Alhawari and Mukhopadhyaya [11]. The results of these reviews all found that the guarded hot plate (GHP), heat flow meter (HFM), in-situ HFM, GHB and CHB thermal testing methods as the most commonly used.…”

“…The GHP method is limited to measuring the thermal properties of flat, homogonous, small-scale samples of individual materials, as it relies on smooth and consistent surface contact between the specimen and the plates [11]. For example, it can provide accurate measurements of the installed insulation RSI-value but cannot accurately measure the thermal properties of a system of materials that would be representative of an actual portion of a building envelope.…”