Energy and Buildings 55 (2012) 94–101 Contents lists available at SciVerse ScienceDirect Energy and Buildings j our na l ho me p age: www.elsevier.com/locate/enbuild Air distribution and ventilation effectiveness in an occupied room heated by warm air Michal Krajˇ cík a,b,∗ , Angela Simone a , Bjarne W. Olesen a a ICIEE (International Centre for Indoor Environment and Energy), Department of Civil Engineering, DTU (Technical University of Denmark), Nils Koppels Allé, Building 402, DK-2800 Kgs. Lyngby, Denmark b Department of Building Services, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 813 68 Bratislava, Slovakia a r t i c l e i n f o Article history: Received 12 July 2011 Received in revised form 11 January 2012 Accepted 15 August 2012 Keywords: Warm air heating Floor heating Thermal comfort Air distribution Ventilation effectiveness Contaminant removal effectiveness Air change efficiency a b s t r a c t Air distribution, ventilation effectiveness and thermal environment were experimentally studied in a simulated room in a low-energy building heated and ventilated by warm air supplied by a mixing ven- tilation system. Measurements were performed for various positions of the air terminal devices and at different simulated outside conditions, internal heat gains and air change rates. Floor heating was also simulated and compared with the warm air heating system. Vertical air temperature profiles, air veloc- ity profiles and equivalent temperatures were derived in order to describe the thermal environment. Contaminant removal effectiveness and air change efficiency were used to evaluate ventilation effec- tiveness. No significant risk of thermal discomfort due to vertical air temperature differences or draught was found. When the room was heated by warm air, buoyancy forces were important for ventilation effectiveness at low air change rates. The effect of increasing air change on the ventilation effectiveness depended on the position of air terminal devices. Depending on the position of air terminal devices, the ventilation effectiveness varied between 0.4 and 1.2, where 1 is complete mixing. When a radiant floor heating system was simulated, the cooler ventilation air introduced to the room mixed well and created uniform conditions with a ventilation effectiveness of about 1. © 2012 Elsevier B.V. All rights reserved. 1. Introduction In low energy buildings the energy demand for space heating is very low and the use of a combination of ventilation and warm air heating may be an interesting alternative to a separate heating system [1]. However, introducing warm supply air to the room may result in a layer of warm air forming under the ceiling and a short- circuit air flow pattern [2–4]. Convective flows due to buoyancy forces are likely to produce air flows larger than the mechanical ventilation supply rates in residential buildings. Convective bound- ary layer flow develops down cold windows and induces a flow field at floor level [5–8], and a considerable amount of air is trans- ported in thermal plumes above internal heat sources. Equations for calculating the amount of air transported in cold downdraughts have been proposed by Andersen [7] and Skistad et al. [8]. The volume flow in the convective plume above a seated person was investigated by Mierzwinski [9] and Danielsson [10], by Zukowska ∗ Corresponding author at: Department of Building Services, Faculty of Civil Engi- neering, Slovak University of Technology in Bratislava, Radlinského 11, 813 68 Bratislava, Slovakia. Tel.: +421 910 68 60 44. E-mail addresses: michal.krajcik@gmail.com, michal.krajcik@stuba.sk (M. Krajˇ cík), asi@byg.dtu.dk (A. Simone), bwo@byg.dtu.dk (B.W. Olesen). et al. [11] above a thermal manikin, and by Mundt [12] and Kofoed [13] above a heated cylinder. The values they reported ranged from about 30 l/s [9] to 90 l/s [11] depending on various factors such as temperature gradient, clothing insulation and the position of a table. Buoyancy forces as a result of cold vertical surfaces and inter- nal heat sources may therefore have a major influence on the air distribution, and consequently on ventilation effectiveness in the room. In his previous investigations Olesen [14,15] reported no serious thermal discomfort for a subject sitting near the window of a well insulated room under winter conditions as a result of radiant temperature asymmetry, vertical temperature differences or draught in a room heated by warm air. However, as dwellings become tighter, this may result in unacceptably low ventilation rates and poor indoor air quality. An acceptable indoor air quality in residential buildings is usually defined by specifying the required level of ventilation in air changes per hour [16], and this may differ according to national standards. The stipulated levels of air change per hour in international or national standards assume perfect mixing, i.e. a ventilation effectiveness equal to 1. Unfortunately, ventilation effectiveness depends on the position of the supply and extract air terminal devices (ATDs) and on the difference between supply and room air temperature [17,18]. When warm air is supplied and exhausted in the upper part of the room, the 0378-7788/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.enbuild.2012.08.015