| With the continuous development of China’s urban integration,the volume of the building industry continues to increase,building energy consumption and building carbon emissions continue to increase,building energy efficiency while increasing the proportion of renewable energy in building energy is the fundamental way out to alleviate the contradictions of building energy and resource constraints.The requirement of air tightness in near zero energy buildings is more stringent,which leads to the indoor air quality of buildings heavily dependent on the guarantee of fresh air system.In early 2020,the sudden outbreak of the epidemic(COVID-19)caused people to pay attention to the indoor air quality.In addition,the poor outdoor air quality in recent years,which has seriously affected indoor air quality.In view of the design and operation regulation of the fresh air of the semi-centralized air conditioning system widely used in actual projects,and from the perspective of building energy saving and improving indoor air quality,this paper proposes a variable fresh air volume design method for the semi-centralized air conditioning system.First,the research significance of variable fresh air volume design for semi-centralized air conditioning system is introduced,and the advantages of variable fresh air volume design in saving energy and improving indoor air quality are illustrated by comparing the differences with traditional semi-centralized air conditioning from the design of fresh air volume to each stage of operation regulation.Subsequently,a fresh air control method based on indoor and outdoor enthalpy as the control variables is proposed for realizing the variable fresh air volume operation of the semi-centralized air conditioning system,and a joint operation control strategy for the air conditioning fresh air system is given.In the transitional season and summer,when the enthalpy of fresh air is less than that of indoor air,the new air system increases the introduction of fresh air to eliminate the building load by using natural outdoor cooling sources,thus achieving the purpose of reducing building energy consumption and improving indoor air quality at the same time.Secondly,we study the method of determining the design fresh air volume of semicentralized air conditioning system with variable fresh air volume operation,give the calculation steps of design fresh air volume and the corresponding solution algorithm,and further form the calculation procedure of optimal design fresh air volume.The energy-saving effect of variable fresh air volume design is also analyzed through specific cases.Compared with the traditional semi-centralized air conditioning system,the cumulative cooling load reduction rate of residential buildings in Dalian area can reach 48.0% after adopting the variable fresh air volume design,and the electricity saving rate of the cooling system is 26.8%.The energy saving effect of variable fresh air volume design of office building is better,the cumulative cooling load reduction rate is 32.0% when the fresh air system is a single fan,and the electricity saving rate of the cooling system is up to 27.7%.Then,the additional investment payback period method is used to analyze the economics of the variable fresh air volume design of the semi-centralized air conditioning system,and the initial investment and operation cost of the two air conditioning system solutions are obtained through the design analysis and simulation calculation of the two cases,and finally it is obtained that: the initial investment increased by the variable fresh air volume design compared with the traditional semi-centralized air conditioning system can pay back the cost within the use cycle(20 years)of the air conditioning system,and the additional investment payback period for the residential building and the office building are 20 years.The additional investment payback periods for residential buildings and office buildings are 9.31 years and 11.68 years,respectively.Finally,the climate suitability of the semi-centralized air conditioning system design method was evaluated in China’s cities by proposing a three-level index zoning method,in which the total number of hours of fresh air available for cooling and the total number of hours of dehumidification were used to represent the climate suitability of the design method for the area.The four types of different climate suitability partitions can be used to judge the applicability of the variable fresh air volume design method in a city,and also the applicability of other energy-saving means that directly use outdoor air to reduce indoor heat and humidity loads,such as mechanical ventilation and natural ventilation. |
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