An electric underfloor heating system has heating cables embedded in the floor. Flow screed is often used in combination with underfloor heating installation. Traces of decorated walls, mosaic floors, underfloor heating and bath suites were discovered. The floor is generally heated by the ondol, an underfloor heating system. Electrical underfloor heating is required to be protected by a 100 mA RCD. The engineering of underfloor cooling and heating systems is governed by industry standards and guidelines. In China and Korea, underfloor heating traditionally is used. A third underfloor module contains cooling systems and an electrical generator. The removable panels for underfloor access simplify maintenance and operations. With underfloor cooling, condensation may collect on the surface of the floor. The underfloor area was sometimes decoratively screened at the perimeter with timber battens. The fuselage has underfloor storage for cargo and baggage. Later a double-bubble fuselage was proposed to give extra underfloor cargo space. Robots then apply the underseal to the underfloor and wheel arches. Despite being underfloor, the generator units (GU) have diesel engines of V12 formation.