Type selection and engineering design of the hotte

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Type selection and engineering design of air-cooled heat pump cold and hot water units

air-cooled heat pump cold and hot water units are a new type of air-conditioning host that began to be applied in China in the 1990s. These units can provide both cooling and heating, eliminating the boiler room and cooling water system, and are flexible and convenient to install. The operation of the unit is controlled by microcomputer with high reliability. Therefore, it is widely used in many air conditioning projects in the Yangtze River Basin. However, due to the different climatic conditions in different regions, plus the lack of experience in engineering design. Therefore, many problems have been found in the use. Based on his engineering experience in recent years, the author of this paper talks about some experiences for the reference of colleagues. In the design process of a project, if the local climate and environment permit, and after technical and economic analysis and comparison, it is determined that the air-conditioning cold and heat source of the project adopts air-cooled heat pump units, then the designers should start to analyze and compare the products of relevant manufacturers at home and abroad, and select a more economical and reasonable heat pump product for users. The main content of model selection is first of all the overall performance analysis of the unit, which includes the refrigeration capacity, heating capacity, COP value, noise, overall dimensions, operating weight and other parameters of the heat pump unit. Secondly, the internal configuration of this kind of heat pump is analyzed, including compressor type, condenser structure and layout, thermal expansion valve configuration, evaporator type, energy regulation mode, defrosting mode, safety protection and automatic control items, etc. After the above analysis and comparison, we can choose a more ideal unit. The next work is to arrange the equipment. In this process, we must consider the reasonable spacing between the equipment, the configuration of auxiliary heat sources and the impact of the overall operation noise of multiple heat pumps on the surrounding environment. The following is about the above aspects. Performance analysis of air-cooled heat pump cooling capacity of air-cooled heat pump: these two parameters are the most critical parameters to determine the normal use of air-cooled heat pump. They refer to the cooling capacity or heating capacity of air-cooled heat pump when the inlet air temperature and inlet and outlet water temperature are under design conditions. It can be found from the product samples provided by relevant manufacturers. However, it is also found in the design that the sample parameters provided by some manufacturers have not been tested, but copied from the relevant samples of other manufacturers. This brings certain difficulties to the correct type selection of designers. Therefore, the author suggests that if conditions permit, designers can obtain the off design performance curve of the compressor from the compressor manufacturer according to the compressor model configured by the air-cooled heat pump of the relevant manufacturer, and check the refrigerating capacity and heating capacity of the compressor under the design working condition of the heat pump according to the design working condition of the heat pump, so as to judge the authenticity of the parameters provided by the sample. COP value of air-cooled heat pump: this value is an important parameter to determine the performance of air-cooled heat pump. Its value directly affects the power consumption of air-cooled heat pump in use. Therefore, units with high COP value should be selected as far as possible. At present, if China only purchases the current purchasing capacity, the COP value is 2.57, the cop of most imported or joint venture brands is about 3, and the value of high-efficiency units of individual imported brands can reach 3.8. Noise: noise is also an important parameter to measure an air-cooled heat pump unit, which is directly related to the impact of heat pump operation on the surrounding environment. Relevant domestic experts have divided the noise of various imported heat pumps into three levels according to the actual measurement of the project. The first level is above 85dB, the second level is between 75 ~ 85dB, and the third level is below 75db. We should give priority to units with noise below 80dB in engineering design and selection. Appearance size: most air-cooled heat pump units are arranged on the outdoor roof. When arranging the equipment, it has clear requirements for the distance between the equipment and the surrounding wall several years ago and the distance between the equipment. Therefore, we must consider whether the selected equipment size meets the size requirements of the equipment layout when selecting the equipment. On the premise of the same performance, the unit with smaller size should be preferred to reduce the equipment, but it does not need the floor area with too high strength and hardness. Operating weight: since most air-cooled heat pump units are arranged on the roof, the bearing capacity of the roof must be considered when selecting the type. If necessary, consult with the structural discipline to enhance the bearing capacity of the roof. However, when selecting equipment, we should give priority to units with light operating weight. System analysis of air-cooled heat pump the so-called system analysis of air-cooled heat pump means that in the selection process of air-cooled heat pump, in addition to comparing their respective refrigeration capacity, heating capacity, COP value, noise, operating weight, overall dimensions and other parameters, they also need to analyze their respective compressor type, condenser type and layout, thermal expansion valve configuration, evaporator type, defrosting mode The energy regulation mode and the automatic control and safety protection of the heat pump system are analyzed, and their respective advantages and disadvantages in system configuration are compared. Compressor type: at present, the compressor types used for air-cooled heat pump mainly include piston type, scroll type and screw type. Fluctuation refers to that (which can be used for power loading) the oil pressure inside the hydraulic servo experimental machine may adopt three types of high-frequency wave action control. According to the characteristics of heat pump, such as long running time and large compression ratio, the author believes that scroll and screw compressors will become the mainstream of heat pump compressors. The reasons are as follows: 1. Compared with piston compressors, scroll and screw compressors have fewer transmission parts, which reduces the friction loss of the compressor and improves the efficiency of the whole machine. 2. Due to the large compression ratio of the heat pump unit, the volumetric efficiency of the piston compressor decreases under the same clearance volume, resulting in the decline of the overall efficiency. Scroll and screw compressors do not have this problem. 3. The working environment of the compressor used for air-cooled heat pump is worse than that of other compressors working under ordinary air-conditioning conditions. The running time of each compressor is also longer, and the range of working conditions is also larger. Therefore, the reliability requirements of the compressor are higher. Scroll and screw compressors have the characteristics of less parts and compact structure, so they are especially suitable for heat pump units. 4. At present, the air-cooled heat pump units generally adopt the method of hot air defrosting to remove the frost accumulated on the air side heat exchanger under the heating condition in winter. At the beginning and end of defrosting, the system needs to operate in the opposite direction. The liquid refrigerant accumulated in the original condensing coil suddenly reduces to the suction pressure and rushes to the compressor, causing the wet stroke of the compressor. This is no big problem for scroll and screw compressors, but it is very easy to cause damage to the air valve and connecting rod for piston compressors. 5. In addition, for the heat pump compressor itself, the noise of scroll type and semi closed screw type is lower than that of piston type

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