Research On The Integration Of Cold And Heat Supply System For Hotel Buildings Based On Two-stage Compression

With the continuous prosperity of the economy and the rapid development of tourism,the number of hotel buildings has increased significantly in recent years,and the functions provided by hotel buildings have been gradually diversified.While meeting the diverse needs of hotel buildings,huge energy consumption has attracted people’s attention.Among them,energy consumption for heating,cooling,domestic hot water and steam production is particularly large.In order to comply with the development direction of China’s total energy consumption control and improve the efficiency of energy systems,so as to achieve the goal of energy conservation and environmental protection.We must optimize the traditional heat and cold energy supply system of hotel buildings.Aiming at the problems of insufficient energy utilization and low system integration in the traditional cold and heat energy supply system of hotel buildings,this paper proposes a new type of system:cold and heat supply system based on two-stage compression.This is based on the cascade utilization principle of physical energy.According to the characteristics of temperature and heat distribution in the refrigerant condensation process,the superheat recovery device,condenser and supercooled device are used to realize the heat matching in the condensation heat recovery process,so as to reduce the irreversible loss in the heat transfer process.Among them,the use of supercooler not only increases the heat recovery,but also improves the unit refrigeration capacity of the refrigerant;the use of two-stage compression intercooling instead of the traditional high compression ratio single-stage compressor can reduce the power consumption and discharge temperature of the compressor,at the same time,it can also preheat steam boiler feed water to achieve full utilization of heat energy and effectively reduce fuel consumption for steam production;In addition,in order to solve the problem of cooling in the inner zone in winter,an evaporator is connected in parallel after the expansion valve I,which not only meets the cooling demand in the inner zone in winter,but also can increase the evaporation temperature of the system and increase the heat capacity.In this study,the first and second laws of thermodynamics were used as the performance evaluation criteria of the system.Firstly,the traditional heat recovery heat pump unit under the same input condition was used as the reference system,and the steady-state performance analysis of the cold and heat supply system based on two-stage compression system and reference system was conducted with Aspen Plus software.The calculation results show that in the cooling and heat recovery operation mode,the COP of the cold and heat supply system based on two-stage compression can reach 7.6,and the exergy efficiency is 54.6%.Compared with the reference system,the total compressor power consumption and the exergy loss are respectively reduced by 10.6%and 20.2%,the system’s total performance coefficient COP and cooling performance coefficient COP_cincreased by 16.9%and 9%,respectively.In the heat pump water heater and cooling mode,the COP of the cold and heat supply system based on two-stage compression can reach 4,and the exergy efficiency is40.5%.Compared with the reference system,the total compressor power consumption and the exergy loss are respectively reduced by 10.3%and 20%,the system’s total coefficient of performance COP increased by 33.3%.Then,deeply analyze the impact characteristics of key integration parameters on the thermal performance of the cold and heat supply system based on two-stage compression,that is,determine the weak links of the system according to the exergy loss rate of each equipment of the proposed system.and on this basis to choose the middle pressure,condensation pressure,refrigerating agent supercooling degree,refrigerating superheating temperature,evaporation temperature and cold supply ratio parameters such as depth analysis.The results show that the COP of the system gradually decreases with the increase of condensation pressure and increases with the increase of evaporation temperature.Under the determined evaporation and condensation pressure,the COP of the system increases first and then decreases with the increase of the intermediate pressure,and there is an optimal intermediate pressure value.In different operating modes,subcooling the refrigerant can effectively improve the COP of the system.As the degree of subcooling increases,the COP of the system increases.Among them,the change of supercooling degree has a greater impact on the system with higher condensing pressure;In the heat pump water heater and cooling operation mode,when the evaporation temperature is as low as-24℃,the compression ratio of the two compressors of the system is lower than 4,the maximum discharge temperature is 118℃,and the compressor is in good operating condition;The cooling supply ratio has a great influence on the system performance.With the increase of the cooling supply ratio,the COP of the system increases linearly,but the cooling supply ratio cannot be increased blindly,which needs to be determined according to the amount of cold needed in the inner area of the building.In general,the system proposed in this study integrates and optimizes the air conditioning unit and hot water unit in the system,which can reduce the use of fuel,rationally use the heat of condensation,increase the system cooling capacity,and increase the equipment utilization rate.Compared with the traditional independent system,this system can meet a variety of energy needs,with better energy saving effect and higher recovery rate of waste heat,so it is very suitable for hotels with a large number of cold and hot needs.