Development and Thermal Validation of a Portable Guarded Hot Box for Steady-State Window U-Value Measurements
Karisma Rahmawati (a), Dian Permata Lestari (a), Hadi Nasbey (b), Nurcahya Pradana Taufik Prakisya (c), Maqbul Kamaruddin (d), Dewanto Harjunowibowo (a*)

a) Physics Education Study Program, Sebelas Maret University, Surakarta, Indonesia
*dewanto_h[at]staff.uns.ac.id
b) Physics Education Study Program, Jakarta State University, Jakarta, Indonesia
c) Informatics and Computer Engineering Education Study Program, Sebelas Maret University, Surakarta, Indonesia
d) Department of ICT Integrated Ocean Smart City Engineering Dong-A University, Busan 49315, Korea
d) Department of Architecture, Institut Teknologi Sumatera, South Lampung Regency 35365, Indonesia

Abstract

Guarded Hot box (GHB) has become popular for measuring the thermal transmittance of materials to investigate building energy efficiency. However, previous studies show that developing a portable apparatus and achieving a fast steady state is difficult. Therefore, this study presents the design, calibration, and validation of a low cost portable guarded hot box (GHB) for in situ measurement of the U value of building materials. We used two insulated cubic chambers equipped with thermoelectric modules, PID temperature controllers, thermocouples, and a heat flux sensor. A 5 mm single pane glass specimen with an area of 0.01 m^2 was evaluated under two wall chamber configurations (uninsulated and aerogel insulated). We calibrated the thermocouple before testing to improve sensor consistency. The experimental results showed that the uninsulated chamber produced an apparent U value of 4.07 0.04 W/m^2K. This underestimated the reference range due to uncontrolled heat losses through the chamber walls. After applying a 3 mm aerogel insulation layer, the measured U value increased to 5.95 0.04 W/m^2K, which is close to published reference values for standard single glass. In terms of energy efficiency, the insulated configuration could reduce average power consumption by 51.25%, indicating that improved thermal stability and energy efficiency of the apparatus were achieved. The findings demonstrate that minimising heat losses is essential for accurate U value determination in compact portable GHB systems intended for field applications.

Keywords: Guarded hot-box- Thermal transmittance- U-value measurement- Heat flux analysis- Building thermal performance

Topic: Energy and Environmental Physics