The Study Of The Flow Pattern Within A Large Space Building With Low Sidewall Air Supply And Middle Sidewall Air Return Based On The Scale Model

Stratified air conditioning systems featured with Low sidewall air Supply and Middle sidewall air Return(LSMR) are widely used in large space buildings for the benefits it brings such as energy saving and comfortable thermal environment. In this paper, studies are conducted towards the air flow pattern and air exchange characteristics between different indoor zones. In addition, the method to calculate the proportion of return air from the none air-conditioning zone is explored, which may provide theoretical basis for the total cooling load calculation of air-conditioning systems with LSMR.Calculating the purging flow rate of a control-volume with Multi-chamber theory is the core mission of this study. As a result, the first step is to ensure the proper use and precise result of the CFD simulation, which provides fundamental data for the Multichamber theory. And the scale model test is carried out to verify the simulation result of the CFD system. A scale model test platform and a series of measuring instruments have been set up to guarantee the measuring accuracy of the system under low speed air flow.This thesis mainly focuses on the following tasks below and has reached several conclusion1. Based on the existing large space building with LSMR system, this study design and build the 1:4 scale model test platform. After a series of thermal performance and horizontal temperature field uniformity test, the settle time for the platform shows to be 5 hours and the temperature is proven uniform horizontally. Based on the characteristics mentioned above, this thesis conducted experiments on the thermal environment and air age.2. To fulfill the unique measurement needs of the scale model experiments, the design and build of autonomous mobile high-precision wireless temperature and humidity measurement system are included in this thesis. With comprehensive use of robot mechanisms, electronic measurement technique and digital wireless communication, the thermal environment in the testing chamber can be measured automatically. 3. The temperature measurement of scale model platform shows that with higher roof heat flux, the average room temperature will increase, which leads to the higher heat retention. While the measurement of air age present that with higher roof heatflux, the gradient of air age within the space is smaller and the air age near the roof is also lower than that in normal case.4. The CFD turbulence model, mesh independence are validated by scale model test platform. The result shows that transition k-kl-ω model can provide better precision under the low speed indoor environment and 2 million large mesh is proven to be suitable in this situation. In summary, the CFD result agrees well with the validation test.5. On the basis of validated CFD simulation, Multi-chamber theory is introduced to study the air flow characteristics. By the height where air return intakes locate, the indoor space with LSMR system is divided into 2 parts, namely, air-conditioning zone and none air-conditioning zone according to the different thermal and flow pattern feature. The return air proportion is calculated by dividing the purging flow rate of the none air-conditioning zone by the total air return rate. With the increase of air supply rate, the return air proportion decreases in the power exponential function, while it is less affected by supply air temperature.6. Due to the lack of necessary information from the CFD solver, k-? RNG model is used for the calculation vertical distribution of air age in the scale model. And the result agrees well with the experiment, which verifies the precision of k-? RNG model in predicting the air age distribution under indoor low speed condition.7. Based on the fact that the more purging flow of a zone, the better ventilation performance is, the purging flow rate of the four control volume within the room is calculated by the Multi-chamber theory for further analysis. The result presents that the purging flow rate decrease with increase of the height and the heat retention near the roof is remarkable. Purging flow rate is less affected by the supply air rate and the purging flow rate within vertical direction of the air-conditioning zone tends to be stable.8. By comparing the air age distribution and the equivalent return air temperature calculated by Multi-chamber theory and CFD simulation, this study confirms that the Multi-chamber theory can reflect the main characters of air flow field.