INFLUENCE OF SUPPLY AIR TEMPERATURE ON UNDERFLOOR AIR DISTRIBUTION (UFAD) SYSTEM ENERGY PERFORMANCE
Tom Webster, Kwang Ho Lee, Fred Bauman, Stefano Schiavon, Tyler Hoyt, Jingjuan Feng, Alllan Daly
Underfloor air distribution (UFAD) systems have received attention in recent years due to a number of potential advantages over conventional overhead (OH) systems. These potential advantages include increased layout flexibility, improved indoor air quality and thermal comfort, and energy savings. In particular, energy performance advantages have been difficult to evaluate analytically due to the lack of simulation tools that accurately model the complex heat transfer processes of stratification in the room and “thermal decay” (supply air temperature gain) in the underfloor plenum. Furthermore, the impact of key design and operating parameters cannot be easily determined without such tools. Fortunately, EnergyPlus v3.1 and beyond now contain validated calculation modules suitable to model these UFAD systems (U.S. DOE 2010). Elevated supply air temperature is one of the distinguishing features of UFAD systems as compared to conventional overhead (OH) systems. In this paper EnergyPlus v3.1 simulations have been used to take a detailed look at the impact of variations in the air handling unit (AHU) supply air temperature (SAT) on the performance of one UFAD system commonly used in U.S. office buildings. The results indicate that raising design AHU SAT produces net savings in HVAC electricity consumption, even though cooling energy reductions trade off against fan energy increases; but the magnitude is climate dependent. However, heating energy (gas consumption) increases with increasing SAT, which tends to counterbalance decreases in electricity consumption. The paper includes a discussion of these somewhat counterintuitive findings.
- There are currently no refbacks.