Mechanical and electrical engineers work together on building design and construction projects. Mechanical engineers design heating, ventilation and air conditioning (HVAC) systems, while electrical engineers design lighting and communication systems. Before construction, they perform research, modeling and prototype testing to develop theoretical designs. During construction, they monitor installation and commissioning of systems. After construction, they ensure systems can function reliably over time through inspections and observations. Mechanical and electrical drawings are produced showing layouts of fixtures, outlets, symbols and other details to guide installation of these systems.