Investigation Of The Factors Influencing Warmair Transport Distance In Impinging Jet Ventilation Systems

With the increase of the proportion of building energy consumption in the whole energyconsumptions, the demand to find a new air conditioning mode to replace the mixing ventilation,which has a low efficiency of ventilation and energy utilization, has become an necessary issue inpractice for engineers and designers. Thus the displacement ventilation (DV) system has receivedmore attention in application. However, the disadvantage that it can only be used for coolingbecomes increasingly obvious. To overcome this disadvantage, a new system known as impingingjet ventilation (IJV) system has been developed and used in buildings. When the IJV system isused for space heating, warm air transport distances (L) directly affect the design of terminaldevice and energy utilization. So in the heating mode, L is one of the key parameters in the designof an IJV system.The effect of the supply air temperature difference, supply velocity, the height of air supplyoutlet and the area of air supply outlet on the flow field and temperature field are studied byemploying computational fluid dynamic (CFD) simulations. The values of L of different operationconditions are estimated and an adequate functional relationship between L and factorsinfluencing the performances of an IJV system on heating mode is obtained by using the responsesurface methodology (RSM).The results indicate that, for non-isothermal jet, with the decrease of supply air temperaturedifference, L increases and the indoor temperature is more uniform. When the area of the airsupply inlet is larger, the effect of supply air temperature difference on L is weaker than that ofsupply velocity, and L increases with the decrease of supply velocity. In an IJV system, Ldecreases as the Archimedes (Ar) number is increased, meaning that the Ar number has asignificant impact on the supply air spreading distance of the IJV system when it runs on itsheating mode.In addition, compared with the other parameters, the effects of the supply height and the inletarea on L are comparatively weak and only have a minor effect on L. In the practical application when L needed to be changed for operation, it is better to change supply set values than tochange the supply height and the inlet area. When the design of the area of supply air inlet isunreasonable, local vortexes will occur in different zones in rooms and then leads to inappropriateflow patterns indoors. Therefore, for the applications of IJV systems, it is important to obtainreasonable area of the supply air inlet.Accordingly, when designing a variable air volume (VAV) and/or a constant air volume (CAV)systems, the regressing functions by using the RSM and the corresponding3D response surfacesand2D contour plots provided in the present study can be used as references for adding the designand optimizing the performances of IJV systems.