Detailed and simplified models of a terminal unit that combines an UFAD system with a floor cooling

• Published in: Applied thermal engineering Vol. 129; pp. 1079 - 1091
• Main Authors: Atienza-Márquez, Antonio, Fernández-Hernández, Francisco, Domínguez-Muñoz, Fernando, Cejudo-López, José Manuel
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 25.01.2018; Elsevier BV
• Subjects: Air; Air flow; Air temperature; Boundary conditions; Convective heat transfer; Cooling; Cooling rate; Flow velocity; Heat transfer coefficients; Sensitivity analysis; Temperature; Ventilation
• ISSN: 1359-4311; 1873-5606
• DOI: 10.1016/j.applthermaleng.2017.10.093

•Two new models of an UFAD system with a floor cooling are developed and validated.•A new correlation for the convection heat transfer coefficient is proposed.•The maximum error of the detailed model for the thermal decay is 8.4%.•The simplified model is simple/accurate enough for use in energy simulation tools.•A nomographic design chart for quick sizing of the system. This paper analyses the thermal behaviour of an underfloor air distribution system (UFAD) combined with a floor cooling, focusing on the thermal decay (TD). Two new models were implemented: a detailed model based on the convective heat transfer coefficient inside the plenum, and a simplified model based on the bypass factor. To validate the models we performed three experiments. Both, detailed and simplified models, reproduce well the measured TD. The maximum relative errors between the predicted and measured TD were 8.4% (transient state) and 1.3% (steady state). Although differences were higher at transient regimen, the terminal unit is designed to operate with smooth changes of the boundary conditions. As the error obtained by detailed and simplified models was near identical, the model based on the bypass factor is recommended because of its simplicity. A sensitivity analysis was performed. We evaluated: (1) the TD as a function of the supply air temperature and air flow rate, (2) the cooling capacity of the floor, and (3) the cooling capacity of the ventilation air. The paper concludes with a nomographic design chart that brings together all the features of the terminal unit, allowing a quick selection of the operating parameters.