| Before 2060,China will achieve zero carbon emissions through energy conservation,emission reduction and afforestation,and fully offset its own carbon dioxide emissions.51% of China’s carbon emissions come from the power and heat industry.The world’s annual air-conditioning electricity consumption accounts for about 10% of the total electricity consumption,which brings huge consumption of power resources.The research on air-conditioning energy-saving technology has attracted the attention of many researchers.The gravity circulation cabinet is a new type of application equipment at the end of the capillary air conditioner.It has a condensate tray inside,which effectively solves the condensation risk when the capillary radiant air conditioner is used in summer.When it is used in winter,it can use a low-temperature heat source to increase the utilization of geothermal resources.Studying the indoor operation characteristics of gravity circulation cabinets and the air distribution characteristics in rooms with different heights will broaden the application scenarios of capillary radiation systems used in areas with hot summers and cold winters.In this paper,the operation characteristics of gravity circulation cabinet are studied by means of experiment and numerical simulation.Firstly,thermocouple,real-time data acquisition system and wireless universal anemometer are used to record the indoor temperature and wind speed information of the test room in summer and winter,and the thermal comfort and energy saving are analyzed.The experimental data in summer show that the average indoor temperature is 22.5～25.4 ℃,the temperature increases with the increase of height,and the indoor temperature gradient decreases with the increase of height.The temperature unevenness coefficient in the working area is small,but the temperature at the ankle of the human body is low due to the sinking of cold air,so the temperature unevenness coefficient is large.The indoor temperature vertical dissatisfaction rate is low,which meets the requirements of class I thermal comfort.The air supply mode of gravity circulation cabinet in summer is similar to displacement ventilation,which is 12.7% higher than the energy utilization coefficient of side air supply system.The winter test data show that the indoor average temperature is 22.8～23.8 ℃,the temperature increases with the increase of height,the indoor temperature gradient first decreases and then increases with the increase of height,and the head foot temperature difference is smaller than that in summer.The temperature non-uniformity coefficients on different indoor horizontal planes are small.The vertical dissatisfaction rate of indoor temperature is lower than that in summer,and the local comfort is better than that in summer,meeting the requirements of class I thermal comfort.The working area of the room where the gravity circulation cabinet is located in winter is in an energy-saving state,but the energy utilization coefficient is 22.5% lower than that in summer.Secondly,under the action of natural convection,the gravity circulation cabinet supplies air from the lower tuyere in summer,giving priority to the heat load in the working area,which is of energy-saving significance for rooms with high floors.In order to analyze the influence of room floor height on the air distribution of gravity circulation cabinet,the air distribution characteristics of gravity circulation cabinet in rooms with floor height of 2.60,3.00,3.50,4.00,4.50,5.00,5.50 and 6.00 m were simulated by CFD.The results show that there are temperature stratification in rooms with different floors,the temperature gradient in the working area is greater than that in the upper space,the temperature difference between head and foot is less than 5.1 ℃,and the temperature difference in the working area（the space with indoor height less than 1.70 m）is within 6.5 ℃.The indoor wind speed is less affected by the increase of floor height,and the wind speed in the working area is less than 0.10 m/s.The temperature and wind speed of the return air outlet of the gravity circulation cabinet change little,and the refrigeration capacity increases with the increase of floor height.The rooms with different floors meet the requirements of class I thermal comfort,the temperature non-uniformity coefficient on each horizontal plane is close,the temperature vertical dissatisfaction rate is 15.8% ～ 20.3%,and the local comfort is good.The energy utilization coefficient of indoor working area is 1.51～1.61,which is in the state of energy saving,about 20% higher than that of side air supply system.Finally,in winter,the gravity circulation cabinet supplies air from the upper air outlet,and the hot air descends from the upper space to the working area.In order to analyze the influence of the floor height of the room on the heating effect and energy saving of the gravity circulation cabinet,the CFD simulation study was carried out on its characteristics in the rooms with floor heights of2.60,3.00,3.50,4.00,4.50,5.00,5.50 and 6.00 m.The results show that the temperature gradient of rooms with different floors first decreases and then increases with the increase of height.The temperature difference between head and foot is less than 1.7 ℃,and the temperature difference in working area（space below 1.70 m indoor height）is less than 2.8 ℃.The indoor temperature decreases with the increase of floor height,and the wind speed in the working area is less than 0.10 m/s.The thermal feeling becomes cold with the increase of floor height.The working area of the room with floor height of 2.60～4.50 m meets the requirements of class I thermal comfort.It is not recommended that the gravity circulation cabinet be used alone in the room with floor height of more than 5.00 m in winter.The temperature non-uniformity coefficient on each horizontal plane of rooms with different floors is small,the temperature vertical dissatisfaction rate is 1.0%～1.3%,and the local comfort is better than that in summer.The energy utilization coefficient of indoor working area is about 1.04,which is in the state of energy saving,but the energy utilization coefficient is lower than that in summer. |
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