Methodology for the Evaluation of Natural Ventilation in ... - Cham

By default, there was no accounting for any effects due to radiation in the CFD model. Throughmeasurements in the reduced-scale air model, it was determined that there was a measurableamount of radiation to the ceiling in each heated zone. The CFD model was modified in order toaccount for the radiation that occurred in these zones. Additional simulations were carried outto obtain the percent of the heat input that was radiated to the ceiling of the model. Bymeasuring the temperatures of the surfaces within the physical model, approximations for theheat transfer due to radiation were made using grey body assumptions for two parallel plates(Incropera and DeWitt 1996). Using the measured surface temperatures of 70 °C at thealuminum plate and 55°C at the ceiling, and an emissivity of 0.7 for aluminum and 0.89 forwood, it was determined that 30 percent of the heat was radiated to the ceiling.6.4 Experimental Equipment and MeasurementsThe equipment used in evaluating and monitoring the reduced-scale air model are presented inthis section, along with a description of the facility in which the physical model was locatedthrough the duration of the experimental procedure. The flow patterns, temperaturedistributions, and heat transfer issues within the model were evaluated using a variety ofinstrumentation and equipment. These pieces of equipment helped to quantify the temperaturedistribution and air velocities within the model.Table 21. Summary of Equipment Used in ExperimentsEquipment Type Experimental UseTest ChamberControlled EnvironmentCR10X Data Acquisition System ThermocouplesKeithley Data Acquisition System ThermocouplesHot-wire Anemometer Air VelocityDraeger Smoke Pencils Flow VisualizationFogging MachineFlow VisualizationInfrared Temperature Gun Surface TemperaturesOmega® Heaters, 5W/in 2 , 500W each Internal Loads6.4.1 EquipmentA well-insolated test chamber was used as the control environment in which the scaled-modelwas placed. Therefore the ambient conditions around the model and the fluctuations normallyseen in typical building environments could be controlled. The MIT test chamber in its entiretyconsisted of a well-insulated enclosure separated into two rooms by a partition wall with a large,double-glazed window. The scale model was located in the main room, a well-insulated singleroom that had a dedicated ventilation and control system to manage the conditions within the testchamber. All walls had an insulating value of R-30, or 5.3 Km 2 /W. The test chamber wasoutfitted with a combination of permanent monitoring equipment and portable measuringdevices.The supply air entered the test chamber through a single duct opening in the corner, and air wasexhausted through a grill ceiling exhaust. Care was taken to ensure that there were no significantdrafts from the supply diffuser blowing on the model that might have affected the measurements.The heating, ventilation, and air-conditioning (HVAC) system that conditioned the test chamber102