external heat gains are almost the same 50 (negligible differences due to different Overhead (Mixing) Air Distribution (OH) 45 room temperature profiles) for the two Underfloor Air Distribution (UFAD) systems, but the cooling load removed by 40 the HVAC system is different. We believe 35 that this is probably due to: 30 • In the OH system, part of the heat is stored in the thermally massive slab 25 during the day and released at night 20 when the system is off. Schiavon, et 13 showed that the mere presence al., 15 of the raised floor reduces the abil10 ity of the slab to store heat, thereby producing for the system with a 5 raised floor higher peak cooling loads 0 compared to the system without a | North | East | South | West | Interior | raised floor. • The airflow through the supply ple- Figure 2: Design day cooling load profiles for overhead (mixing) and UFAD systems for five num tends to remove heat from the zones of the middle floor of a three-story office building in Baltimore. The HVAC system concrete slab and the raised floor operates from 5 a.m. to 7 p.m. panels. The difference in cooling loads between OH and UFAD radiation (Figure 2). The correlation equation for UCLR is also evident in the core zone that is not affected by solar captures these differences, although their impact on annual Zone Cooling Load (W/m2 ) 1 3 5 7 9 11 13 15 17 19 21 23 1 3 5 7 9 11 13 15 17 19 21 23 1 3 5 7 9 11 13 15 17 19 21 23 1 3 5 7 9 11 13 15 17 19 21 23 1 3 5 7 9 11 13 15 17 19 21 23 www.info.hotims.com/30919-55 64 ASHRAE Journal September 2010