The higher the ambient temperature, the faster aging processes can occur. In (almost) all emergency power systems with a day tank, the emergency power system engine is kept warm for a quick start with a cooling water temperature of up to 47 °C. The day tank is usually kept at the same temperature as the engine. The day tank is usually installed in the same room as the emergency power system and is exposed to increased temperatures due to the waste heat from the engine, which leads to faster fuel aging. If the main tank is installed in a separate, well thermally insulated room, often it is also located underground outside the building, the fuel aging process is slower there.
Another factor is copper fuel supply lines between the tank and the engine that may be installed in PSUs. Non-ferrous metals have a catalytic effect and cause the fuel to age more quickly.
Engine manufacturers for emergency power systems usually recommend the use of diesel fuel for system operation. However, diesel is only available in a blend with up to 7% biodiesel. This blend is designed for short-term consumption in transportation, but not for long-term storage. As the storage period of this blend increases, the risk of fuel-related malfunctions due to aging processes and possible microbiological infestation of the fuel increases.