An approximate parametric model for quantifying the thermal mass with harmonic variation of outdoor air temperature

The appropriate use of thermal mass (TM) in buildings can maintain thermal comfort and reduce building energy consumption, and this depends mainly on reasonably estimating the amount of building heat storage when meeting the allowable indoor air temperature variation range. However, there is a lack of a general model to evaluate the effect of TM on indoor air temperature. Because the existing models can neither estimate the effective heat capacity (EHC) of building external walls nor consider the effects of window heat transfer on indoor air temperature. To overcome the limitations, the temperature elasticity factor (TEF) is introduced to describe the relationship between the temperature of the inner surface of the external wall and indoor air temperature, and EHC is proposed to quantify TM. A second-order effective heat capacity (SEHC) model is then developed by employing the TEF and EHC with the consideration of heat transfer through windows. The results by the SEHC model show good agreement with those of the previous models. Furthermore, the SEHC model is applied to a case study on room ventilation. The results show that decrement factor will be overestimated, and time lag will be underestimated without considering the influence of window heat transfer and EHC of external TM on indoor air temperature. The SEHC model, combined with the database models of EHC and TEF, can provide an accurate, effective, and systematic tool for architects and engineers to estimate the impact of TM on the indoor air temperature in the early stage of architectural design.