Final answer:
The correct option is d. Throughout the heating process.
The gas valve is energized during the ignition process in an induced-draft furnace, and it continues to deliver fuel throughout the heating process once proper ignition is achieved.
Step-by-step explanation:
In an induced-draft furnace employing hot surface ignition, the gas valve assumes a crucial role in the ignition sequence to ensure a safe and controlled start-up of the heating system. During the ignition process, the gas valve is energized to provide a carefully metered supply of gas to the hot surface igniter. This methodical delivery of gas is essential for the controlled ignition of the furnace.
The hot surface igniter, typically composed of a ceramic material, heats up when energized, reaching a temperature that facilitates the combustion of the incoming gas. By energizing the gas valve at the appropriate stage of the ignition sequence, a regulated amount of fuel is introduced, allowing for the safe and controlled initiation of the combustion process. This sequential approach mitigates the risks associated with uncontrolled gas release, ensuring the safety of the furnace operation.
Once the flame is established and proper flame sensing is confirmed, signaling that ignition has occurred successfully, the gas valve continues its operation. It remains energized to deliver a consistent flow of fuel to sustain the flame throughout the heating process. This continuous fuel supply is vital for maintaining a steady and reliable heat output, contributing to the furnace's overall efficiency and performance.
In summary, the gas valve's energization during the ignition process in an induced-draft furnace with hot surface ignition is a systematic and safety-focused approach. It allows for the controlled release of gas to the hot surface igniter, ensuring a secure and efficient ignition sequence. Once the flame is established, the gas valve remains active to provide a continuous fuel supply, sustaining the desired heating conditions throughout the furnace's operation.