Which system is primarily affected by low grain temperature?

Low grain temperature primarily affects ventilation systems. In the context of agricultural settings, particularly when it comes to grain storage, maintaining proper temperature and airflow is crucial to prevent spoilage and mold growth. Ventilation systems are designed to manage the ambient temperature and moisture content around the stored grains. When the grain temperature is low, it can lead to condensation if there are fluctuations in humidity, which may then cause spoilage.

While heating systems can also be impacted by temperature variations, and cooling and refrigeration systems play roles in lowering temperatures, they are not directly concerned with the specific issues that arise from low grain temperatures in storage contexts. Therefore, the correct answer highlights the role of ventilation systems in maintaining an optimal environment for grain storage by addressing issues related to low temperatures and ensuring adequate air circulation.