Development of continuous surface temperature monitoring technique for investigation of energy release characteristic by building fabrics
Student thesis: Doctoral Thesis
This study proposes a novel technique, continuous surface temperature monitoring (CSTM), that uses infrared technology to estimate nocturnal sensible heat (SH) transfer between buildings' finishing materials and the surrounding environment, without knowing physical and thermal properties of the tested materials. The CSTM technique includes two major parts: (1) capturing surface temperature change by infrared camera; and (2) formulation of equations for calculating sensible heat transfer from simply the surface temperature change, i.e. no further inputs of physical and thermal properties of the finishing materials are required. It is critical to study the contribution of heat transferred by building fabrics to the Urban Heat Island (UHI) effect because of the increasing threat of global warming. The basic principle of CSTM technique is that the total energy change of an object is closely correlated to the surface temperature change. The sensible heat transfer, mainly by convection and radiation, from building finishing materials to the environment is reflected in its surface temperature change. Therefore, the total nocturnal sensible heat loss can be estimated by integrating the total surface convective and radiative heat flux curves respective to the total releasing time after sunset (e.g. 4:00 pm to 6:00 am). On the other hand, assuming that the internal energy change is equal to the energy loss to the surroundings, another simple method to estimate sensible heat release by an object is to calculate the total internal energy change of an object, namely, Internal Energy (IE). Its magnitude is the product of the object's mass, m, its specific heat, c, and its temperature change, ∆T. Therefore, IE method is applied to verify the effectiveness of the CSTM technique. In this study, sensible heat release of three common building fabric materials, concrete, marble and ceramic, are derived by using both the CSTM technique and the IE method. 47 repeated measurements were carried out on the samples for comparison. The results show that sensible heat release levels estimated by CSTM are satisfactory, with only 1.8-5.2% difference compared to the IE method. Besides, the CSTM technique was also verified in outdoor environments; field tests were carried out at two locations, Kowloon Tong and Central, in Hong Kong. Nocturnal sensible heat loss by different building fabrics are examined and compared. The results show that buildings with granite panels installed by hanging on the concrete block (i.e. air gap is formed) are always having higher surface temperature than other forms of wall designs. Furthermore, factors affecting the surface temperature change and hence the energy transferred are discussed. Unlike the various simulation methods by different programs, e.g., AUSSSM, 3D-CAD, Envimet and Ecotect, etc., the developed CSTM technique opens a door for simple in situ measurement of actual energy release by different building fabrics which can enhance investigation of impact of building fabrics in urban heat island effect studies.
- Thermal properties, Exterior walls