A waste heat source is available at 400°C. A heat engine operates using heat from this source. It rejects heat to the surroundings at 38°C. The power from the engine runs an air conditioner to keep the air inside a building at 25°C, rejecting heat to the surroundings at 38°C. Heat leaks into the building at the rate of 1 kW per degree temperature difference between the surroundings and the temperature inside the building. What is the minimum required heat transfer rate from the waste heat source?