Equivalent room air temperature based cooling load estimation method for stratum ventilation and displacement ventilation

Cooling load estimation is the base for the design and control of the air conditioning system. The indoor air temperature stratification of stratum ventilation and displacement ventilation contributes to the energy saving, but challenges the cooling load estimation. The existing building simulation tools are generally equipped with only the fully mixed air model and ignore the indoor air temperature stratification. This study proposes an equivalent room air temperature based cooling load estimation method to enable the fully mixed air model to accurately estimate the cooling load of stratum ventilation and displacement ventilation. The equivalent room air temperature is the air temperature with which the fully mixed air model can produce the same cooling load as that of stratum ventilation/displacement ventilation. The equivalent room air temperature is modelled as a function of the supply air temperature, supply airflow rate and room air temperature of stratum ventilation/ displacement ventilation using response surface methodology. Case studies using the experimentally validated multi-node models are conducted to demonstrate the effectiveness of the proposed method. The mean absolute errors in the cooling load estimation by the proposed method for the constant-air-volume system and the variable-air-volume system are 0.02% and 5.78% respectively under stratum ventilation, and 0.07% and 4.78% respectively under displacement ventilation. Compared with the conventional method, the proposed method improves the accuracy in the cooling load estimation by 70.92%-99.94%.