Civil Engineering Reference
In-Depth Information
Fig. 8.11
Under-fl oor air distribution CV
discharge air is usually cooled down to only around 63 °F instead of 55 °F which is
normally done in traditional systems), but also creates higher occupant comfort by
delivering air with lower speed than what is used in traditional systems, and where
it is most effective. ASHRAE standard 55 (ASHRAE
2010
) recommends a maxi-
mum vertical air temperature difference of 5 °F between heights of 67 and 4 in. from
the fl oor which is usually where the occupants head and foot are located. Cooling
air stratifi es towards the ceiling where the air fi nds a return path to the air handling
unit and creates a comfortable occupied zone in the lowest six feet of the room
where actually occupants live and then leaves the room with a higher temperature
through the upper unoccupied section of the room and fi nally from available path on
the ceiling. In regards to the advantages of any confi guration of the under-fl oor sys-
tems over the traditional systems, it easily can be seen that the under-fl oor air distri-
bution systems are more energy effi cient due to its required higher cold air
temperature for air conditioning. In addition even more energy saving opportunity
is created any time the room sensible load decreases. In this condition the supply air
temperature can be increased to even higher than 63 °F and results in an even larger
decrease in cooling consumption. Also, there is a much larger chance and available
opportunity for utilizing the economizer cycle for this system due to the higher
possibility of outdoor air temperature meeting the economizer cycle acceptable
requirements. Another energy saving opportunity appears as the result of lower con-
sumed energy by the air handling unit fan, due to lower pressure loss in the system
compare to the traditional systems with extensive duct network. In addition it is
