Effects of external heating sources on the airflow and ventilation efficiency

Rabanillo-Herrero, Mario; Padilla-Marcos, Miguel; Feijó-Muñoz, Jesús; Meiss, Alberto.
Conferencia: WMCAUS 2018 en: Praga, CZ. Junio 2018

Buildings are important sources of energy consumption, representing approximately 40% of the primary energy consumed in Europe. From it, the greater energy expenditure which occurs in buildings corresponds to the air conditioning of interior spaces. The effect of temperature of the heating system elements is a parameter that could affect the airflow in terms of buoyancy and thermal comfort and that should be studied to ensure the quality of ventilation. This study aimed to assess the air change efficiency and thermal comfort with three thermal conditioning systems (radiators, underfloor heating and radiant ceiling) in winter conditions, varying its position in the interior space. This can be used by architects and engineers when planning the position of the heating systems or refurbishing a room. The experimental analysis was developed in the test chamber of the Laboratory of Ventilation of the University of Valladolid, serving as validation of multiple CFD simulations. For this research, 8 case studies were assessed, with a reference case which did not include any heating system, showing only the behaviour of the air in winter when entering an interior environment; 5 cases with the arrangement of a radiator in five different positions inside the premise and 2 final situations which corresponded to the room equipped with underfloor heating and radiant ceiling. At the reference case, the results showed an air change efficiency of 47.50%, with a great feeling of discomfort caused by the low temperature of the outdoor air and the room, which forced in the air a downward trend through the centre of the room and not ventilating properly in the upper parts. The use of radiators showed a small improved efficiency between 47.67% and 49.90% and a PPD improvement of 12.18%. The low operating temperature of the underfloor heating did not correct the downward pattern of the air but provided good thermal comfort and, on the other hand, the radiant ceiling was able to temper the air flow and provide a more homogeneous temperature in the occupied volume. The results show that, being the thermal comfort achieved, the mean air change efficiency varied only 2.40% among all cases, which makes temperature not a significant influence, being the air change efficiency more influenced by other factors such as geometry, air velocity or flow. Even so, the trajectory of the airflow in the premise would be affected by the thermal action, due to the convective effect, presenting great differences according to the location of the thermal systems. Thus, the air trajectory could falter when it entered the room or rise towards the ceiling creating areas with lower temperature in its centre. With all the above, it seems that the position of the radiator below the air inlet seems to be the most appropriate since, even within the similarity of efficiency results, it provides the best air change efficiency and thermal comfort and therefore demonstrates the wisdom of constructive tradition and its choice to place the radiator in that position.