[Greenbuilding] Automated Insulated Plug

[Eli]

Does any body have experience with an automated insulated plug that would
open when summer night fan that is pulling cool air through house from the
crawlspace.  We want to set a differential thermostat to turn fan on when
outdoor air is cooler than interior air.  What we are looking for is a
product that can open a vent that is insulated with the use of an electric
control (switch).  We are locating fan in insulated crawl space so as to
cool the bottom of suspended slab.  Suspended slab is a great way to avoid
over heating of your house.  The fan is not located in the attic.  Therefore
the operable panels that are attached to fan will not work.

Eli Fishpaw