For the room/return plenum, the model performs a steady-state heat balance on each of the three major architectural layers of the heat transfer system: (1) the top surface of raised floor (carpet), (2) the bottom surface of slab (or slab insulation, if present), and (3) the suspended ceiling (if present, assumed to be a uniform temperature [infinite conductivity]).
To investigate possible strategies for reducing the magnitude of energy transferred into the underfloor plenum, the model was configured to include different combinations of low-emissivity ceiling and slab insulation.
In this configuration, the slab insulation layer also had a low-emissivity coating on its lower, exposed surface and was installed directly on the underside of the structural slab or structural layer between floors of a multistory building (Figure 2).
The baseline and three cases represent different combinations of slab insulation and low-emissivity ceiling.
When slab insulation is combined with a low-e ceiling, the best distribution of energy flows is achieved.
In addition, to ensure comfortable cooling operation, it is critical that (1) control and operating strategies be used, such as reducing the plenum inlet temperature, increasing the room airflow rate, and actively controlling of room air stratification or (2) other design decisions be employed, such as slab insulation, low-e ceilings, or other approaches for reducing the impact of heat gain into the supply plenum.
R-10 slab insulation was selected for all simulations because it represented a more practical choice that reduced the steady-state slab heat transfer (compared to no insulation) by only 19% less than that of R-30 insulation.