Fraction (SPF), Zone Fraction (ZF) and Return Plenum Fraction (RPF) are developed similarly to calculate the supply plenum, zone and return plenum cooling load. UFAD design tools for zone airflow requirements There are two available design tools for determining zone airflow rate requirements for UFAD system, one is developed at Purdue University as part of the ASHRAE Research Project (RP-1522). The other one is developed at Center for the Built Environment (CBE) at University of California Berkeley. ASHRAE Research Project (RP-1522) developed a simplified tool that predicts the vertical temperature difference between the head and ankle of occupants, the supply air flow rate for one plenum zone, number of diffusers and the air distribution effectiveness. The tool requires users to specify the zone cooling load and the fraction of the cooling load assigned to the underfloor plenum. It also requires users to input the supply air temperature either at the diffuser or at the duct but with the ratio of plenum flowrate to zonal supply flowrate. The tool allows users to select from three type of diffusers and is applicable to seven type of buildings, including office, classroom, workshop, restaurant, retail shop, conference room and auditorium. The CBE UFAD design tool based on extensive research is able to predict the cooling load for UFAD system with the input of the design cooling load calculated for the same building with an overhead system. It also predicts the airflow rate, room temperature stratification, and the plenum temperature gain for both interior and perimeter zones of a typical multi-story office buildings using UFAD system. The CBE tool allows the user to select from four different plenum configurations (series, reverse series, independent and common) and three floor-diffusers (swirl, square and linear bar grill). An online version of the design tool is publicly available at Center for the Built Environment. Plenum air temperature rise Plenum supply air temperature rise is the increase of the conditioned air due to convective heat gain as it travels through the underfloor supply plenum from the plenum inlet to the floor diffusers. This phenomenon is also named thermal decay. Plenum air temperature rise is caused by cool supply air coming into contact with warmer than air concrete slab and raised floor. According to a modeling study, air temperature rise can be quite significant (as much as 5 °C or 9 °F) and subsequently, compared to an idealized simulated UFAD case