When operating the BPU in temperatures below -25° F, the Digital Control System uses what to heat the coolant for proper engine startup?

In the context of operating the BPU (Backup Power Unit) in extremely cold temperatures, it’s essential to ensure that the coolant is adequately heated for proper engine startup. When the temperature drops below -25°F, a fuel-fired coolant heater is utilized to provide the necessary warmth to the coolant. This type of heater burns fuel to generate heat, which is then transferred to the coolant, ensuring that it remains at a temperature conducive to engine operation.

A fuel-fired coolant heater is effective in these situations because it can produce significant heat energy, which is critical in extreme cold conditions. It allows for reliable engine startup by preventing the coolant from freezing and ensuring that the engine components can function correctly once the system is engaged. This method of heating is particularly useful in harsh environments where other heating methods might not be as effective or reliable.

Other types of heaters may have limitations in efficiency or capacity when dealing with very low temperatures, which is why a fuel-fired heater is the preferred choice in such scenarios.