This study investigated the energy conservation of a non-insulated old apartment with a ventilated sunspace in Qingdao, China. The ventilation between the bedroom and sunspace of the apartment was controlled by the Delta temperature, which is equal to the sunspace temperature minus the bedroom temperature. EnergyPlus software was used to calculate the temperature, humidity, and thermal load of the apartment. The aim of this research is to analyze the sunspace performance at different flow rates and Delta temperatures. The flow rate between the sunspace and bedroom was set to range from 0.05 m3/s to 3 m3/s, and the Delta temperature was set to range from 0 to 2°C. It is found that when the ventilation between the sunspace and bedroom is activated under the condition that the Delta temperature is higher than 0.5°C, the heating load energy consumption decreases with increasing flow rate. When the flow rate is 0.3 m3/s and the Delta Temperature is 1.5°C in February, and the flow rate is 0.3 m3/s and the Delta temperature is 1°C in November, December, January, March, and April, the minimum energy consumption of the bedroom is 198.8 KWh/m2. Compared with bedroom without sunspace and with non-ventilated sunspace, Delta temperature-controlled ventilated sunspace can reduce the annual heating load energy consumption by nearly 14.7% and 4.4%, respectively.