U.S. patent application 20150245532 (assignee Acta Technology Inc., Boulder, Colo.):
"This invention is a novel air supply register that modulates the incoming air supply from the under floor air duct. This air register is able to monitor the air temperature leaving the server stack thereby improving the response time of the HVAC system. Since the register has adjustable louvers that can modulate the inlet air flow into the server stack; it will save energy by reducing the supply air to the server stack when the cool incoming air is not needed. This reduces hot spots in the data center because the cool incoming air can be directed to server racks that need cooling. This self-modulation of the air register is not available in conventional floor registers. ... [Power units use] a phase change material to move the said louvers through said linkages so that the outlet air of the said air register can be modulated."