Abstract

Condensing boilers achieve high efficiency through latent heat recovery; however, oversizing can lead to efficiency loss due to short cycling. This study investigates short cycling in a residential apartment. Under low-load conditions, the flow rate decreases to approximately 1.2 L/min, causing the supply water temperature to rise to about 90°C and triggering boiler shutdown due to overheating. As the indoor temperature has not reached the setpoint, repeated restart and shutdown cycles occur, resulting in short cycling. Consequently, the average supply temperature (~67.5°C) fails to meet the target. Maintaining a minimum flow rate and considering flow conditions in boiler sizing are essential to prevent short cycling.