Each unit measures and stores data separately, before being transferred centrally for further analysis. One unit is located indoors to measure the air temperature, surface temperature, and heat flux through the material, while the other unit is located outdoors to measure the air and surface temperature. The existing measurements, as per BS-9869-1, use offline and hardwired data acquisition equipment. The heat flow method, described in BS ISO 9869, has been widely employed to measure the thermal transmission properties of building structures that consist of homogeneous layers perpendicular to the heat flow. To present a technological background, some widely used methods for the thermal performance evaluation of in-situ measurement (the focus of this paper) are summarized below, together with their advantages and disadvantages. Other in-situ approaches, such as infrared (IR) thermography and calculation methods, have also been developed to evaluate thermal transmittance and thermal resistance. The hot box method is commonly used in a lab environment, while the heat flow method has been recommended in the BS ISO 9869 for in-situ measurements. Measurements can be done in a laboratory (ex-situ) or on-site (in-situ). The thermal performance of building materials can be characterized using thermal transmittance (U-value), thermal resistance, thermal conductivity, and diffusivity. It directly relates to the thermal comfort of the building occupants, as well as the energy consumed for heating or cooling.

It describes how building materials respond to the ambient environment in the daily or seasonal cycle. The thermal performance of building materials is an important factor that greatly affects a building’s energy performance and efficiency, i.e., it is used for the energy auditing of new and existing buildings.

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