Comparison Of Indoor Thermal Comfort With Three Main Air Supply Modes

The selection of the air supply mode at the end of the air conditioning system not only relates to the building energy consumption but more relates to people’s requirements on the comfort level of the room with an air conditioning. With the increasing improvement of the living standard, people no longer only require the air conditioning to reduce the temperature and relieve summer heat, and they have raised the higher requirements on the supply air temperature, speed and comfort level, as well as humidity. Indoor air quality relates to people’s work efficiency, and the environmental attributes are closed related to the ventilation pattern. For this reason, research on the air supply mode of the particular building has received more and more attention.The traditional central air conditioning systems for buildings are: the primary air fan-coil system, the centralized constant air volume system as well as the variable air volume system. Generally, these systems adopt the ceiling air-supply(upward air-supply) conditioning mode which emphasizes the intensive mixing of air-supply airflow and the indoor air. The floor air supply outlet is generally set flush with the ground. The air supply enters inside the room through the floor air supply outlet, and it discharges from the air outlet of the upper room(above the ceiling or the working area) after the heat and mass transfer occurs between the air supply and the indoor air. The floor air supply mode is relatively widely applied in the foreign countries; however, its application in China is still in the development stage because it has the certain requirement on the storey height and its cost is relatively high.This topic selects the best option mainly by comparing the temperature field and velocity field as well as PMV under the floor air supply, displacement ventilation and the mixing ventilation patterns through the simulated data. The conclusion is drawn by comparison: under the mixing ventilation mode, the vertical temperature gradient is small and the indoor temperature is uniform; however, the ventilation efficiency is relatively low and the energy consumption is relatively high. Under the displacement ventilation mode, thermal stratification of airflow is generated and two areas appear: the lower unidirectional flow area and the upper mixing area; its ventilation efficiency is high than that of the mixing ventilation but the supply air momentum is low. The floor air supply mode has the relatively good energy conservation and air quality and has some characteristics of thermal stratification, so it is the optimal decision.Through the numerical simulation method, the analytical investigation is carried out on the indoor thermal comfort and air quality of adopting the floor air supply system, and the main energy-saving potential influencing the effect of the floor air supply, to analyze distribution of the indoor temperature field, velocity field and PMV under different supply air temperatures and different supply air volumes and to conclude the recommended values of the supply air temperature and the supply air volume for the office buildings.