Application Of Ground-source Heat Pump System In Guang 'an Area

The ground source heat pump has been promoted in China as a new energy utilization method with high energy efficiency and low pollution.In the southwestern regions,the ground source heat pump system is used,and there is an imbalance in the heat extraction and release of soil,Most of them use a compound system.There are many technical issues that need to be studied,including load calculation,cold and heat source system design,unit selection,unit group control scheme design,underground heat exchanger design,and system performance evaluation and prediction..This paper studies the application of the soil source heat pump compound system in an industrial park in Guang'an area.The project includes 36 buildings with a heating and cooling area of 246,391m2 and a domestic hot water heating area of 48,729m2.(1)Collect building parameters and user information,simulate calculation of user air conditioning load and domestic hot water load.(2)Research literature,design cold and heat source system using ground source heat pump technology(3)Design the underground heat exchanger scheme with the soil thermal response report parameters;(4)Establish the soil heat transfer model of the underground heat exchanger(5)Proposed unit group control scheme to solve the problem of imbalance between users' cold and heat;(6)Based on the underground heat exchanger model,conduct rapid simulation test on the performance of the cold and heat source system and group control schemeThis article uses the Designbuilder software with EnergyPlus as the core to model and simulate the user's hourly cooling and heating loads throughout the year.The air conditioner summer peak load is 18448.79 KW summer total load 89139.51KWH;winter peak load9095.20 KW winter total load 5871218.79 KWH,winter and summer load imbalance rate is34.13%.The thermal load of domestic hot water for the whole year is 1849462.92 KWH.This paper proposes a composite system plan of "heat recovery soil source heat pump+ soil source heat pump + chiller ".Choose 3 2900KW(cooling power)/ 3100KW(heating power)ground source heat pump units,1 960KW(cooling power)/ 1020KW(heating power)heat recovery ground source heat pump unit,4 2200 KW chiller units;1 unit 750 KW high temperature ground source heat pump hot water unitIn order to simulate the long-term performance of the system,a one-dimensional finite element numerical heat transfer model of a vertical U-tube underground heat exchanger is proposed.The input parameters are borehole hourly load and borehole hourly flow,and the output parameters are hourly temperature distribution of the soil and hourly water temperature of the borehole.Comparison with TRNSYS shows that the maximum difference between the results for the entire year does not exceed 1 ° C,the deviation is less than 0.2 ° C in 52.85%and less than 0.6 ° C in about 80%.It can be considered that the annual simulation accuracy of this model is equivalent to TRNSYS.The calculation time of the model is about 13 min throughout the year,which can quickly obtain results and is suitable for long-term performance prediction of multiple schemes.The "heat pump-underground heat exchanger coupling calculation model" for testing the group control scheme and the corresponding underground heat exchange scheme is proposed.Its input parameters are: hourly unit load,hourly chilled water flow,hourly cooling water flow,Initial heat pump unit evaporator side outlet water temperature,borehole initial outlet water temperature,underground heat exchanger parameters(number of boreholes,hole spacing,hole depth,borehole thermal physical parameters).The output parameters are borehole heat absorption,borehole water temperature,and borehole soil temperature distribution.Three types of unit group control schemes are proposed:(1)Group control scheme one is to give priority to ground source heat pump units in summer to bear the summer load.After all heat pump units are fully loaded,turn on the chiller unit to bear the remaining load.(2)The second scheme of group control is that in summer,the load not greater than 960 KW is fully borne by the full heat recovery ground source heat pump,the chiller unit is responsible for the50% of the load greater than 960 KW.ground source heat pump is responsible for the remain 50%.(3)Group control scheme three is that the operation rules of the first four years of the unit operation are the same as scheme one.Starting from the fifth year,the cooling tower is connected to the underground heat exchanger tube group during the transition season(March,April,May,and October).When the temperature difference between the tower outlet temperature and the borehole wall temperature is greater than 1 ?,turn on the cooling tower to cool the soilReferencing the soil thermal response experiment and the plan of the underground heat exchanger corresponding to the three group control schemes,3 group control schemes were proposed.Group control scheme 1 initial underground heat exchanger scheme 1: the number of boreholes is 2300,the borehole depth is 100 m,and the hole spacing is 6m.Group control scheme 2 initial underground heat exchanger scheme: the number of boreholes is 2100,the borehole depth is 100 m,and the hole spacing is 6m.Group control scheme 3 initial underground heat exchanger scheme: the number of boreholes is 2300,the borehole depth is100 m,and the hole spacing is 6m.The above scheme adopts the "heat pump-underground heat exchanger coupling calculation model" dynamic simulation for 30 years continuous operation.The first annual cumulative heat absorption is 5339716.8KWH,the cumulative heat release is9485923.95 KWH,and the annual soil-side cumulative cooling heat The unbalance rate is about 43.70%.In the 12 th year of continuous operation of the unit,the outlet water temperature of the buried pipe will reach 32 ° C,and the ground source heat pump unit will not be able to operate normally.Scheme 2,the cumulative heat release of the underground heat exchanger throughout the year is 5394108.23KWH;the cumulative heat absorption is 5243896.20 KWH.The cumulative imbalance rate of cold and heat throughout the year is about 2.78%,and the cold and heat balance is better.The outlet water temperature of the unit's underground heat exchanger in the 30 th year of unit operation is 23.5 ° C,and the unit can be operated continuously for at least 30 years.Scheme 3 The average heat dissipation of the single hole in the underground heat exchanger during the cooling season is 4111.95 KWH,and the heat dissipation in the heating season is 2042.09 KWH.The heat absorption of the single hole in the recharging season gradually increases with the year of recharging,and the average single hole absorbs heat2612.12 KWH.This scheme can guarantee the unit to run continuously for 25 years.In the25 th year,the effluent temperature of the underground heat exchanger has exceeded 32 ?,and the unit cannot be operated.It is recommended to adopt the group control scheme 2 and its underground heat exchanger scheme and the group control scheme 3 and its underground heat exchanger scheme.In summary,this paper calculates the cooling and heating load of the project,studies the configuration of the ground source heat pump composite system,establishes a rapid calculation model for the heat transfer of the underground heat exchanger,designs and optimizes the underground heat exchanger,and proposes and verifies the three unit group control Through dynamic simulation,a long-term group control scheme is obtained.The work of this paper has a good demonstration effect on the optimization design of the ground source heat pump composite system in the cold winter and hot summer area.