Comparative Study on the Heat Transfer via Unheated Spaces Based on Correction Factor

The accurate assessment of heat transfer via unheated spaces is an important aspect of calculating the heating load of a building and mitigating its energy consumption and carbon emissions. Currently, the majority of international and national standards employ the correction factor method for the calculation of heat transfer via unheated spaces, categorized into three types: detailed temperature correction factors (b), simplified b-values, and a correction factor (a) of thermal resistance. In order to provide an accurate and efficient evaluation of heat transfer through unheated spaces, this paper conducts a comparative analysis of these three methods using on-site measurements, TRNSYS (version 18) simulations, and analytical calculations. The findings indicate that the use of simplified b-values results in inaccurate predictions of correction factors and heat transfer via unheated balconies, yielding relative discrepancies within the ranges of 0.065 to 0.527 and 12.2% to 111.3%, respectively. Detailed temperature correction factors offer a more precise prediction, exhibiting relative discrepancies of −0.161 to 0.11 and 0.1% to 33.5%. However, the complexity of the calculation process, influenced by dynamically changing climates and solar radiation, necessitates a steady-state assumption to streamline calculations. The use of detailed correction factors of thermal resistance yields more accurate predictions, with relative discrepancies ranging from −0.176 to 0.11 and 0.3% to 33.1%, and it is recommended as the main method for predicting heat transfer via unheated spaces. In addition, it is advised to enhance the thermal resistance correction factor method by considering the influence of radiative heat transfer via transparent envelopes.

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