Study And Optimization On Characteristics Of Underfloor Air Distribution System With Perforated Tiles/Grille Diffusers

Heating, ventilation and air conditioning (HVAC) systems have been widely used in many parts of the world. Nowadays, the purposes of HVAC system are mainly focused on the improvement of indoor thermal comfort (ITC) and indoor air quality (IAQ). Nevertheless, the better ITC and IAQ usually mean more energy consumption. As one of the forced air ventilation methods, the underfloor air distribution (UFAD) system has been a subject of active research for its potential advantages of better ITC, IAQ, and energy saving. However, a better distribution of airflow and temperature is critical to achieve the advantages of UFAD system. Therefore, the airflow and temperature distribution in the perforated tiles/grille diffusers UFAD system is researched with simulations and experiments in this study. The details and the main conclusions are as follows:The coefficients of the air leakage and the velocity ratio are proposed account for the characteristics of the UFAD system with perforated tiles, and thus the ideal model for the velocity and pressure in the underfloor supply air plenum (USAP) is optimized. The effect of air leakage on the distribution of velocity and pressure in the USAP is considered in the optimized model, and the measurement of the boundary conditions is also simplified with this model. Furthermore, the coefficients of the air leakage and the velocity ratio are verified with the experiments.The characteristics of thermal decay in the USAP are analyzed for the different terminal device systems. The effects of SAT, airflows, and type of the terminal device on the thermal decay in the USAP are discussed in details with the coefficient of thermal decay, and thus the rules for the variation of the coefficient of thermal decay are derived from the experiments. Furthermore, the fundamental understanding of thermal decay in the USAP for different terminal device is concluded, which is also a guiding significance of configuring the USAP.The key parameters for the thermal stratification as well as the coefficient of temperature gradient are proposed base on different terminal device in the UFAD system, and thus the regression models for the key parameters and the coefficient are derived from the experiments. Furthermore, the model for calculating the airflows is deduced according to the regression models, which simplify the calculation of airflow for the UFAD system. In addition, the control of the thermal stratification and the cooling load calculation also can be achieved on the basis of these models.The new and unconventional way of conditioning the interior zones in UFAD buildings by employing large-area perforated tiles/grille diffusers is proposed, and thus the temperature distributions for the UFAD system with swirl diffusers, perforated tiles, and grille diffusers are compared. The effects of SAT and airflows on the temperature distribution for the UFAD system with perforated tiles/grille diffusers are discussed in depth, which will help to understand the characteristics of the airflow and temperature distribution for the UFAD system with perforated tiles/grille diffusers.To improve the temperature distribution and energy consumption in the UFAD data center, a method on the basis of optimizing the airflow distribution is proposed. The optimized model is validated in the grille diffusers UFAD data center, and then the cold aisle in this data center is closed for the purpose of further optimization. With the optimized model, the temperature distribution in the UFAD data center with grille diffusers is improved effectively without any additional energy consumption. Furthermore, the results also provide guidelines for the application of this method.