However some drop ceiling designs create a.
Attic space vs plemum space.
Unventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings.
Plenum trusses create a reverse bulkhead in the center of the attic space where ducting can be housed in an insulated area.
Don t use the foamed attic space as a conditioned plenum.
Think about the volume of space normally associated with return air ducts vs the volume of space involved in an attic space.
This allows intensive cooling to be pumped through the space under the floor to cool the servers switches routers etc.
However i have two questions if i want to centrally air condition my entire house.
That dead air space is designed to be a buffer between the roof.
The velocity of the overall air movement within the two spaces would be substantially different at the same cfm.
A basement is below and an attic is above the main part of the house.
This by definition is a plenum air space and requires plenum rated cable.
A plenum space is a part of a building that can facilitate air circulation for heating and air conditioning systems by providing pathways for either heated conditioned or return airflows usually at greater than atmospheric pressure.
That space typically has about a 10 12 degree difference than the conditioned space below it.
Rarely will a sealed foam insulated attic deviate more than 15 degrees from the living space temperatures below it.
So when we have a choice we prefer hvac systems located under the house.
It will increase your load and contaminate your house air if it has been converted from a ventilated attic to a sealed attic.
The energy savings touted by unvented attics can be as high as 20.
Space between the structural ceiling and the dropped ceiling or under a raised floor is typically considered plenum.
A two room addition on the 1st floor has limited attic space and a 4 crawl space.
It s easy to see your point about eliminating ductwork from the attic.
Cabling between the many devices and to the users runs through this open floor space.
However if moisture is able to enter the unvented attic space it may lead to roofing panel issues.