A convective heat transfer model for simulation of rooms with attached wall jets

Scope and method of study. Surface heat transfer rates were measured in a well-instrumented, room-size enclosure (12' x 16' x 10' high) for two opposing active surfaces (a 'hot wall' and a 'cold wall') each consisting of 20 heated or chilled panels. The purpose of the study was to develop a local variable based convection model suitable for implementation in building simulation computer programs. The scope was limited to radial ceiling diffuser configurations and included data from the experimental room at the University of Illinois (UIUC) as well as data from the experimental room constructed at Oklahoma State University (OSU) for this research.; Finding and conclusions. A local Reynolds number based explicitly on the characteristics of the offset wall jet was defined. Both the local velocity and the length scale were based on offset wall jet theory. A forced convection model based on the local Reynolds number was developed. The correlation was based on measured ceiling and wall data from the UIUC room over a range of 3 to 100 air changes per hour (ACH) and wall data from the OSU room over a range of 10 to 30 ACH. The correlation was applied to both walls and ceilings with uniform and variable surface temperatures over the entire range of measured flow rates. A metric to determine the type of local flow regime (natural or forced convection) was also developed. The new correlation was implemented along with three previously published correlations in a building simulation program. The room cooling loads predicted by each of the four convection correlations were compared to measured cooling loads from the OSU experimental room. The local variable based correlation improved the predicted cooling load by at least 20% over the entire range of ventilative flow rates.