A new terminal unit combining a radiant floor with an underfloor air system: Experimentation and numerical model

• Published in: Energy and buildings Vol. 133; pp. 70 - 78
• Main Authors: Fernández Hernández, Francisco, Cejudo López, José Manuel, Fernández Gutiérrez, Alberto, Domínguez Muñoz, Fernando
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.12.2016; Elsevier BV
• Subjects: Accuracy; Air quality; Air temperature; Buildings; Comfort; Comsol multiphysics; Condensates; Cooling; Cooling radiant floor; Cooling systems; Error analysis; Experimentation; Experiments; Flooring; Mathematical models; Modules; Numerical model; Numerical prediction; Pipes; Radiant cooling; Response time; Temperature effects; Thermal decay; Thermal response; Thermodynamic properties; Underfloor air distribution system; Water distribution systems; Thermal decay; Comsol multiphysics; Underfloor air distribution system; Cooling radiant floor; Numerical model
• ISSN: 0378-7788; 1872-6178
• DOI: 10.1016/j.enbuild.2016.09.040

•The paper presents a new terminal unit combining a radiant floor with an underfloor air system.•The thermal behavior of this unit is analyzed by means of a numerical model and three experiments.•Air ventilation thermal decay in the plenum is negligible when air is introduced at outside conditions, and about 2.7°C when air is treated in the DOA.•The new terminal unit is like a radiant cooling floor and a UFAD system working separately, but integrated in the same terminal unit. This paper investigates a novel terminal unit that integrates a radiant cooling floor (RCF) with an underfloor air distribution system (UFAD). The unit consists of rectangular modules that are installed above the standard structural floor of the building, creating a raised floor. The upper face of these modules incorporates a grid for easy installation of the pipes of the RCF, while the space between the raised floor and the structural slab is used as the air supply plenum of the UFAD system. The proposed system presents some advantages over the standard air systems: (1) it allows increasing production and zone set point temperatures, which improve the efficiency of the chiller plant, (2) improved comfort, and (3) improved air quality due to reduced mixing within the occupied zone. The proposed system can also solve or mitigate some of the drawbacks of cooling floors: (1) prevent water condensation over the surface of the floor, (2) increase the cooling capacity of the floor, and (3) reduce the response time to changes in the space thermal loads. The interactions between the RCF and the UFAD are not evident. In this paper, the thermal behavior of the combined unit is investigated by means of a numerical model implemented in COMSOL Multiphysics. The accuracy of this model is checked against three experiments undertaken in laboratory using a scale model of the system. In the first experiment, the air above the floor is kept quiescent and the cooling capacity is measured. The maximum relative error between the predicted and measured capacities is 19.5%. The numerical model is then used to study how the air movement within the plenum modifies the transient thermal response of the unit. The second and third experiments are designed to quantify the temperature change of the air circulating within the plenum (thermal decay or TD). In nominal operating conditions, TD is about 2.7°C. In short, the new terminal unit is like a radiant cooling floor and a UFAD system working separately, but integrated in the same terminal unit.