Comparative Analysis of Air Conditioning Systems in Commercial Office Buildings: Cost, Energy and Comfort

Abstract

Heating Ventilation & Air Conditioning (HVAC) systems prevalent in Australian office buildings are Variable Air Volume (VAV), Under Floor Air Distribution (UFAD) and Chilled Beams (CB). This study compared these systems with respect to cost, energy, and comfort. Using an A-B comparison research design, structured feedback was provided on comfort vectors and system preferences by a randomised sample of 30 human subjects recruited from the industry. The findings showed thermal comfort preferences for CB as being 62% versus 38% for VAV and UFAD. Logistic Regression analysis, like the approach taken in food and wine evaluations, found that skin temperature difference between the head and leg to be statistically significant when comparing CB with VAV (p < 0.032) and UFAD (p < 0.003). A human shaped skin-temperature controlled thermal manikin validated the results of the human subject’s experiments. The equivalent temperature analysis accounted for the effects of HVAC systems on asymmetrical environmental conditions, with CB outcomes confirming the adage -‘cooler head and warmer feet offers better comfort’. Life cycle cost (LCC) saving was 3.9% for a UFAD system and 7.8% for a CB with VAV as the base, over a 30-year period. By considering that CB and UFAD systems require less floor-to-floor heights compared to a VAV system, the finding highlighted the potential for generating significant additional revenue through rental income by incorporating an extra floor within the building height restriction. Utilising EnergyPlus-DesignBuilder, energy modelling, UFAD was found to be less energy efficient by 2.4% and CB as more energy efficient by 4.9% using VAV as the base. Evaluations were carried out of the HVAC systems with respect to COVID transmissibility and included as an Annexure. Key Words: Chilled Beams, Energy Efficiency, Life Cycle Costing, Thermal Manikin, Thermal Comfort, Under Floor Air Distribution, Variable Air Volume.