Performance and Optimization of an Underfloor Air Distribution System in an Educational Building in a Hot and Humid Climate
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Today there is a proliferation of different HVAC system configurations. Design and performance of each HVAC system are dependent on climate and the intended use of the building. Energy recovery ventilation is becoming more common in new buildings and is one of the more popular retrofit options in hot and humid climates. Currently there is a lack of optimization strategies that involve the underfloor air systems combined with Energy Recovery Ventilation (ERV) especially in hot and humid climate. This thesis examines the performance and optimization of underfloor air distribution systems (UFAD) in hot and humid climates. This thesis also compares the UFAD system performance to a typical overhead air handler unit (AHU) system found in Texas. The performance comparison is done with EnergyPlus modeling software. Separate sets of models are created to examine performance of at different operational parameters. The minimum air flow rates are modeled at 0.1 cfm/ft2, 0.2 cfm/ft2, 0.3 cfm/ft2, 0.4 cfm/ft2 for both UFAD and overhead (OH) systems. The supply air temperatures were modeled at 55 °F, 60°F, and 63 °F. Outside air strategies include simple economizer, energy recovery ventilation (ERV), as well as a combination of both economizer and ERV. The study found that at low minimum (0.1 cfm/ft2) flow rates an overhead system will slightly outperform a UFAD system (OH 2.6% cheaper to operate than UFAD) while at 0.3 cfm/ft2 a UFAD system is more efficient (UFAD 14.8% cheaper to operate). The outside air strategies have the same energy savings effect on both systems. The UFAD system has a higher peak cooling load and a lower peak heating load compared to the overhead system. This thesis also covers the stratification and supply air temperature measurements within two offices inside the Mitchell Physics building, located on the Texas A&M campus. The stratification measurements showed that on average the stratification was lower than expected for such systems with office 411 having average stratification of 1.8 °F and office 423 average stratification of 1.5 °F. Temperature measurements at the diffuser level showed some reheat, especially during unoccupied periods such as early mornings, late evenings and weekends, even when the outside temperature was above the interior thermostat set point. System level total supply air flow rate showed little variation with a minimum of 0.47 cfm/ft2 and a maximum of 0.59 cfm/ft2. The analysis of energy recovery wheel operation concluded that the low exhaust air flow of only 0.2 of the outside air is responsible for the low temperature difference observed in the outside air stream through the ERV.
Khmelenko, Vasiliy (2015). Performance and Optimization of an Underfloor Air Distribution System in an Educational Building in a Hot and Humid Climate. Master's thesis, Texas A & M University. Available electronically from