The non-certificated student pilot reported that, while taxiing to the runway and adjusting the throttle, the engine spooled up and the taxi speed increased. He retarded the throttle and attempted to apply toe brakes. The airplane was equipped with a hand brake instead of toe brakes. The certified flight instructor (CFI) reported that the airplane moved toward a hangar at a "rapid speed" as he tried to slow the airplane. The airplane collided with a hangar door, resulting in substantial damage to the airframe. The CFI stated that the time from loss of control to the collision with the hangar was about two to three seconds. The CFI had 1.9 hours of experience in the accident airplane. The pilots reported that there were no anomalies or malfunctions with the airplane during the accident sequence.