Research On Selection Of Outdoor Design Temperature For Air Source Heat Pump System In Severe Cold And Cold Regions

With a large number of low-temperature air source heat pump(ASHP)products adopting new technologies arising,the application of ASHPs is prevailing in severe cold and cold regions of China.However,the heating capacity of the ASHP unit during application is actually affected by the temperature fluctuation and the degree of frost formation.So,there is some doubt as to whether the heating capacity is reduced,and the non-guarantee days are prolonged if the outdoor design temperature used for the selection of conventional heat source is adopted when selecting ASHP units,and whether it is necessary to re-select the outdoor design temperature for the selection of ASHP units.This is the focus of this thesis.In this thesis,11 typical cities in severe cold and cold regions of China are selected,the hourly outdoor temperature and relative humidity in the heating periods of these 11 typical cities are analyzed,and the low-temperature adaptability and frost severity of ASHPs in these 11 typical cities are evaluated.Subsequently,a power function model is used in this thesis to determine the relationship between the heating performance and outdoor temperature and quantify the influence of outdoor temperature on the heating capacity of ASHP unit.Furthermore,in order to quantify the influence of frost formation on the heating capacity,the concepts of frostingdefrosting heat loss coefficient and nominal heating capacity loss coefficient are quoted,and the calculation models of these loss coefficients are established.Then,a typical building is set as a research object in this thesis.In the beginning,the nominal heating capacity of the ASHP unit is preliminarily selected based on the outdoor design temperature for heating as the design condition.And then,the hourly actual heating capacities are calculated according to the calculation model.At last,heat supply and heat demand are compared to determine whether the equilibrium is achieved.As a result,when the outdoor average temperature is equal to the outdoor design temperature for heating,the heat supply can counterbalance the heat demand without considering the frost formation.But after the frost formation is taken into consideration,the heat supply cannot answer to the heat demand in some cities.When the outdoor average temperature is equal to the outdoor design temperature for winter ventilation,the phenomenon of insufficient heat supplying in the ASHP heating system is more obvious than that in the conventional heating system.Then,the indoor temperature conditions are analyzed,and the it is found that the minimum indoor daily average temperature in the ASHP heating system is significantly lower than that in the conventional heating system.Combined with the statistical result of the number of non-guarantee days,the result indicates that the number of non-guarantee days is universally increased after the ASHP heating system is applied.Therefore,the outdoor design temperature for heating is re-selected specifically for ASHP units so that the new ASHP unit can meet the equal comfort requirement of conventional heating system(The non-guarantee days are 5 days).And the appropriate auxiliary heat source is configured in the form of electric heater and heat pump,respectively.Finally,in order to further improve indoor thermal environment,the feasibility of heating when the outdoor temperature is below 8?(?8? heating mode)is put forward,and the increase of energy consumption after adopting ?8? heating mode is analyzed and in the thesis.The result shows that the increase of energy consumption is generally not very large in the most area of severe cold and cold regions,but it will be a significant increase of energy consumption in some cities where the latitude is relatively low,and the heating season is relatively greatly prolonged after adopting ?8? heating mode.So,the increase of operating cost should be taken into consideration in these cities.