CBE UFAD Cooling Design Tool

CBE UFAD Cooling Design Tool logo

The Center for the Built Environment's research team has developed a simplified, practical design procedure and associated software tool to determine cooling load requirements of underfloor air distribution (UFAD) systems. These are provided to improve the accuracy of airflow, thermal decay data, thermal comfort calculations, system design, and the operation of UFAD buildings. Screen Shots


UFAD, underfloor, Cooling load calculator, cooling, stratification, thermal comfort



Expertise Required

Knowledge about cooling load calculation and UFAD.




Practicing architects and engineers involved in the design, specification, and analysis of UFADs. Instructional tool in colleges and universities. Design/build UFAD contractors, facility engineers, energy service consultants, and UFAD and raised floor manufacturers.


User needs to input:

  • Plenum configuration (series, reverse series, independent plenums, or common plenums)
  • Room height (interior and perimeter)
  • Floor area (interior and perimeter)
  • Floor level (ground, middle or top)
  • Diffuser type (interior: Swirl or variable air volume directional interior; and perimeter: variable air volume directional perimeter or linear bar grille)
  • Number of diffusers (interior and perimeter)
  • Design cooling load for overhead system (interior and perimeter)
  • Design average temperature in the occupied zone (interior and perimeter)
  • Estimated category 2 leakage (interior and perimeter)
  • Set point temperature of air entering the supply plenum
  • Number of occupants
  • Zone orientation (north, south, east or west)
  • Exterior wall length

How a user enters data: text boxes and drop-down menus


Information presented (results given for interior and perimeter):

  • Airflow (through diffusers)
  • Airflow (through diffusers and leakage)
  • Diffuser discharge temperature
  • Air temperature at 4 in. height
  • Return air temperature
  • Return plenum air temperature
  • Average temperature in the operational zone
  • Temperature difference between the head (67 in.) and the ankle (4 in.)
  • Airflow per area (through diffusers)
  • Airflow per diffuser
  • Design airflow per area (through diffusers and leakage)
  • Design cooling load calculated for an overhead (mixing) system
  • UFAD cooling load ratio (UCLR)
  • Supply plenum fraction (SPF)
  • Zone fraction (ZF)
  • Return plenum fraction (RPF)
  • UFAD cooling load
  • UFAD cooling load per area
  • Supply plenum cooling load
  • Supply plenum cooling load per area
  • Zone cooling load
  • Zone cooling load per area
  • Return plenum cooling load
  • Return plenum cooling load per area

Form of the output: pre-formatted table of results, exportable as CSV file, and 2 graphs showing interior and perimeter temperature based on height

Computer Platform

Created for Opera, Firefox, and Chrome (Internet Explorer not supported)

Programming Language



The tool can account for key differences between UFAD and traditional mixing overhead (mixing ventilation) systems. These include: (1) the difference between design day cooling load profiles; (2) the impact of a thermally stratified environment for UFAD versus well-mixed for overhead, and (3) the impact of heat transfer (temperature gain) in underfloor air supply plenums. The new design tool allows the use of a familiar load calculation procedure for overhead mixing systems as input to the UFAD design tool. The tool is a reasonable compromise between EnergyPlus simulations (very detailed but time consuming) and cooling load tool calculations based on the full mixed air hypothesis and simplification on the thermal behavior of the supply plenum. The tool allows the user to test several plenum configurations, diffuser types and numbers, and thermostat set points.


The conversion factors from the cooling load calculated for an overhead systems (mixing ventilation) and the UFAD cooling load are a valid within the boundary conditions of the simulations performed to develop the tool. Only UFAD diffuser types present in EnergyPlus were studied.



University of California Berkeley


University of California Berkeley
390 Wurster Hall, #1839
Berkeley, CA 94720-1839
United States






Free use here: http://cbe.berkeley.edu/ufad-designtool/online.htm