Abstract: The research status of air-conditioning condensation heat recovery in China is introduced in this paper. The feasibility of air-conditioning condensation heat recovery, the classification of recovery, the form of recovery, the problems in application and so on are reviewed. Research direction of heat recovery. Keywords: Condensation heat recovery 1 Introduction Energy is one of the five elements that human beings rely on to survive and is an important strategic material for national economy and social development. The rapid economic development must be based on the supply of energy, especially electricity. China's energy structure, a large proportion of raw coal, up 75%, China's coal consumption accounts for 27% of the world's total coal consumption, is the world's only coal-based energy consumption power, extensive use of coal and lack of Effective governance has caused serious environmental pollution. The energy utilization rate is relatively low. At present, China's energy utilization rate is still over 10% lower than that of advanced industrial countries. Its energy consumption per unit of GDP is 6 to 10 times higher than that of advanced countries, and its energy consumption per unit of production is 50% higher than that of other countries % ~ 100% [1]. The structural and inefficient use of energy not only affects our country's economic construction and development, but also affects the surrounding environment on which we depend for existence. HVAC project as one of the main energy-consuming technologies, we must base ourselves on the rational use of energy and effective energy-saving measures. Feasibility of Air Conditioning Condensing Heat Recovery Conventional air conditioning systems consist primarily of refrigerant circulation, cooling water circulation, chilled water circulation and air circulation. In the refrigerant cycle, the gas refrigerant is compressed in the compressor, the temperature increases, the pressure increases; through the exhaust pipe, high pressure gas refrigerant into the condenser is cooled by cooling water, into a high pressure liquid; through Throttling valve, the pressure is reduced, the high-pressure refrigerant into a low-pressure gas-liquid mixture containing a small amount of gas; thereafter the refrigerant in the evaporator at constant pressure (low pressure) absorbs a large amount of heat in the evaporator of chilled water evaporates into a low pressure gas Refrigerant; gaseous refrigerant back to the compressor through the suction line. In the cooling water circulation, the cooling water absorbs the heat of the refrigerant in the condenser, and then is pumped to the upper part of the cooling tower for heat and moisture exchange with the counter-current (rising) air to lower the cooling water temperature. Cooling water is then pumped to the condenser for heat exchange with the refrigerant, the temperature rises, and so on. Air conditioning room cooling load (ie, heat) into the evaporator through the evaporator cycle, into a part of the condensation heat, and then through the cooling water circulation to the atmosphere [2]. Therefore, the conventional air conditioning refrigerator, the main role is to air conditioning, air conditioning system, the heat of condensation directly discharged to the atmosphere is not used. The refrigeration unit emits a large amount of condensing heat to the atmospheric environment when operating under air conditioning conditions, usually with the condensing heat up to 1.15 to 1.3 times the refrigeration capacity [3]. A large amount of condensation heat directly into the atmosphere, lost in vain, resulting in greater energy waste, the heat of the distribution of the surrounding environment and then the temperature increases, causing serious environmental pollution. If the condensation heat released by the refrigerator is used to heat domestic hot water and production process hot water, not only the pollution caused by condensation heat can be reduced, but also an energy-saving method that turns waste into treasure. In recent years, more and more studies have been done on the heat recovery of condensation heat rejection of air conditioning systems. 3 China's air conditioning condensing heat recovery with the status quo With the development of our national economy and people's living standards, China's air-conditioning penetration rate increased rapidly; the same time, due to changes in people's living habits and hygiene requirements, residential buildings more and more The more attention to the supply of sanitary hot water. At present, most of the hot water supply needed by domestic families in daily life is provided by special hot water heaters. This has further exacerbated the energy shortage and environmental pollution in the world and has drawn great attention from all countries. Therefore, in recent years, more and more studies have been done on the preparation of domestic hot water from the heat recovery and condensation heat recovery of the air conditioning system in China. 3.1 Condensing heat recovery classification Condensation heat utilization can be divided into direct and indirect. Direct refers to the refrigerant from the compressor into the heat recovery device directly after the heat exchanger with tap water to prepare domestic hot water. Indirect refers to the use of conventional air conditioning condenser side of the high-temperature air or 37 degrees of water to heat the preparation of domestic hot water. Indirect due to more equipment to be added, the heat transfer efficiency is relatively low, so the technology is not easy to promote. Direct and can be divided into two categories, one is only the use of compressor outlet steam sensible heat, steam sensible heat generally accounts for about 15% of the total condensation heat [4] [5], in accordance with the demand for hot water and heat Draw the number of heat recovery unit, the other condensation heat is taken away by the cooling water in the condenser; the other is to use the full condensation heat. The two comparison as the former only use the steam sensible heat, heat recovery pressure drop is relatively small, making the condenser pressure is relatively stable on the impact of refrigeration is relatively small. 3.2 Condensing heat recovery form China in recent years, research and application of condensation heat recovery forms are the following: 3.2.1 dual condenser heat recovery technology Rong Guohua [6] proposed: the summer use of the refrigerator condenser heating tap water can Provide hot water and reduce energy consumption. To use chillers to heat tap water, chillers with water-cooled condensers should be used. When tap water is used as cooling water, the amount of water should be matched with the cooling load of the building and the cooling water volume of the refrigerator to ensure the safe and normal operation of the refrigerator. However, the variation rules of cooling load and cooling water quantity of all kinds of buildings vary with the regularity of their tap water consumption, and it is more difficult to achieve the best match. To solve this problem, Sun Zhi Gao, Li Shuhong [7] in the air conditioning system energy recovery energy-saving analysis envisaged the deployment of heat storage device condensing heat, cooling water, hot water consumption imbalance. Wu Xianzhong et al [8] for the characteristics of the steam compression refrigeration unit, put forward to directly meet the hot water consumption tap water into the heat recovery heat exchanger, the use of compressor exhaust heat and partial condensation latent heat to heat it, high temperature heat Water is stored in the water tank for use. Gong Qicai, Chang Shijun et al. [9] combined with the previous research based on the analysis of the exergy from the perspective of heat recovery condensate heat and proposed double-condenser heat recovery technology (Figure 1), the compressor and the condenser A heat recovery (condenser) is added to recover the heat of condensation. The refrigerant coming out of this additional heat exchanger is either a vapor-liquid mixture or gaseous and the remaining condenser absorbs the remaining heat. Figure 1 double condenser heat recovery cooling schematic diagram technology can be directly recovered according to the requirements of the cooling unit of the steam sensible heat or heat plus part of the latent heat to a one-time heating or recycle heating to the specified temperature of water. This form is mainly used in central air conditioning chillers. 3.2.2 household air conditioners commonly used forms of heat recovery Household air conditioners are widely used in our country, but also the number of heat recovery is one of the important directions. Lin Hong [10] discussed the recycling and utilization of domestic air-conditioning condensing heat, and pointed out: Domestic air-conditioning condensing heat recovery system as an effective method to recover low-grade energy can be widely applied to the transformation of ordinary household air-conditioning systems, and its application Energy saving prospects. Harbin Institute of Technology, Jianghui Min, Wang Yang et al [11], put forward in the study of their own household air conditioners for heat recovery form (Figure 2). In this form, the high-temperature and high-pressure refrigerant vapor discharged from the compressor in the air conditioner is injected into the hot water heat exchange device for heat exchange to heat domestic hot water. If the heat exchange capacity of hot water heat exchanger can independently bear all the condensation heat, you do not need to use the air-cooled condenser, on the contrary, you must use both air-cooled and water-cooled condenser to bear all the condensation load. Figure 2 Schematic diagram of the heat recovery of household air conditioners with hot water supply 3.2.3 Heat Pump Recycling Techniques Yu Yingjun and Wang Mengyun [12] discussed the ways and feasibility of recovery of condensation heat. As the air-conditioning cooling water temperature is generally 30 ~ 38 ℃, is a low-grade heat, in order to fully recover the need for heat pump technology, by the refrigerator and heat pump unit to form a combined heat recovery unit. The device is connected to the heat pump evaporator and cooling water circuit, more suitable for the air conditioning cooling water system in the transformation, control is relatively easy to achieve. Yin Yingde, Zhang Ling and others [13] proposed this typical form of indirect heat of condensation after heat recovery (Figure 3). When the chiller and heat pump work at the same time, the cooling water return temperature can be controlled by controlling the start-stop of the cooling tower fan. Through the electric three-way valve to control the cooling tower cooling water flow and heat pump evaporator flow ratio, the heat pump evaporator water temperature below 32 ℃, in order to ensure the normal operation of chillers. This kind of way is in the original system parallel set of heat pump units, the condensation heat as a heat pump heat source to prepare hot water. Figure 3 Schematic diagram of a heat recovery using heat pump 3.2.4 Phase change material recovery Air conditioning condensation heat Xi'an Jiaotong University Liu Hongjuan, Gu Zhaolin [14] proposed the use of phase change material recycling air conditioning condensation heat recovery form. Regenerative heat accumulators replace double condensers. The condensers at the compressor outlet in the heat recovery technology are connected in series with conventional air-cooled condensers (or cooling towers), using cooling towers to remove the residual heat that the heat recovery system can not store. The temperature of the phase change material in the heat recovery heat accumulator varies with the condensation temperature. Initially, the conventional air-cooled condenser (or cooling tower circuit) is closed and the heat recovery heat accumulator utilizes the sensible and latent heat of condensation of the superheating section of the refrigerant to heat the phase-change material, at which point the condensation pressure increases with the heat recovery heat accumulator Phase change material temperature rises and rises. When the system condensing pressure reaches the limit value, open .gunsq1 li {display: block; float: left; width: 200px; overflow: hidden;} ã€Purchase】 fire pump, spray pump, sewage pump 】 ã€Air Valve ã€Purchase】 Signal Amplifier ã€Purchase】 Valve ã€Purchase】 Centrifugal Pump ã€Purchase】 Vertical Multistage Pump ã€Purchase】 Cylinder ã€Procurement】 Speed ​​Controlled Frequency Conversion Motor Previous: New Heat Pump Technology Becomes Air Conditioning Energy Saving Focus Next Posts: US soil - gas-based ground source heat pump technology in China's promotion
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