In the recently announced national energy sector long-term plan, we put forward the idea of ​​energy technology development in 2020, that is, to save energy in the first place and promote the establishment of an energy-saving society; to take coal as the main body and take power as the center to accelerate the development of hydropower and nuclear power. To ensure the safety of oil and gas; adhere to the combination of far and near, and actively promote the development of renewable energy and new energy. One of the priority themes is to strengthen the development of energy-saving and energy-efficient technologies. The development and promotion of new advanced air-conditioning systems and equipment is one of the key technologies for energy-saving technologies in the construction sector. The gas heat pump air conditioning system is an air conditioning system that uses natural gas as the main energy and drives the vapor compression heat pump with an engine. The primary energy utilization rate is up to 1.4 or more, and it has high efficiency, environmental protection, power peaking and gas filling. The advantage is that the energy utilization in the heating mode is about 50% higher than that of the air source heat pump.
1 Hybrid gas heat pump air conditioning system and its energy analysis model 1. Hybrid gas heat pump air conditioning system In the operation of gas heat pump air conditioner, the gas engine is usually operated under partial load conditions, when the operating conditions frequently change with the heat pump air conditioning load When the engine is usually deviated from the calibration condition, the change of the engine operating condition is mainly achieved by controlling the fuel flow. As the fuel flow changes, the operating conditions of the engine frequently change, the engine running stability deteriorates, the thermal efficiency decreases, and the discharge increases. Based on the research of existing hybrid technology and gas heat pump technology, this paper proposes a new hybrid gas heat pump air conditioning system (Hybrid Power GHP, HPGHP) that combines hybrid power system and heat pump. In the power system of the system, the reasonable matching of the two power sources of the gas engine and the battery pack can keep the gas engine in the optimal fuel economy zone, and at the same time improve the gas engine emissions, achieve low system emissions and fuel economy. Good goal.
1 Parallel hybrid gas heat pump air conditioning system principle 1. 2 HPGHP system gas engine dynamic load characteristics In the parallel hybrid gas heat pump system, the shortcoming of the traditional gas engine startup is overcome by the motor starting, under the specified working conditions The control strategy always controls the engine to operate in an efficient area as shown.
The engine high efficiency zone has an upper critical power P t and a lower critical power P d , and the critical power of the gas engine start and stop is P 0 . When the compressor demand power P c is in the range of P t～+∞, the gas engine operates under the P t condition, and the insufficient power is borne by the battery pack; when the compressor demand power P c is in the range of P d～P t When the gas engine automatically adjusts the speed to adapt to P c; when P c is in the range of P 0 to P d , the gas engine operates under the P d condition, and the rich power charges the battery; when P c is 0 to P When the range is 0, the gas engine is stopped, and P c is completely borne by the battery pack.
1. 3 HPGHP system battery dynamic load characteristics similar to gas engines, in order to improve battery cycle life and charge and discharge performance, the battery also has a state of charge (SOC) upper and lower critical point (20% ~ 80%) As shown. During the operation of the system, the state of charge of the battery must always be within the critical range of the SOC. When the SOC approaches the lower critical point, the discharge should be stopped immediately. Otherwise, the battery will be over-discharged and affect the performance of the battery. The engine is responsible for the compressor load and charging the battery; when the SOC approaches the upper critical point, the charging needs to be stopped immediately, otherwise the battery will be overcharged and the performance of the battery will be affected.
Through the control of the gas engine working area and the battery SOC state, while meeting the air conditioning load, the relevant control strategies and methods are established, and the system minimum fuel consumption and the optimal heat pump air conditioning system performance are the control targets, which can achieve energy saving and fuel improvement. The purpose of utilization.
1. 4 Two kinds of dynamic energy coupling simplified mathematical model in HPGHP system Compared with the conventional gas heat pump air conditioning system (GHP) engine, the HPGHP system engine has lower calibration power, because in the HPGHP system, the battery pack is gas. The power of the engine acts as a peak-filling valley. The power required by the compressor that meets the air-conditioning load can exceed the maximum power of the engine. In a conventional GHP system, the power required by the compressor that meets the air-conditioning load must be within the power range of the engine. The two energy coupling processes in the HPGHP system are shown.
In order to simplify the calculation, the following assumptions are made: 1) Assuming that the battery pack in the HPGHP system passes a compressor demand load cycle, the state of charge SOC returns to the initial state of charge, that is, the battery pack is charged during a compressor demand load cycle. All the electricity is discharged, all the electricity is discharged from the charged electricity; 2) the heat dissipation of the battery pack during charging and discharging is not considered; 3) It is assumed that the compressor demand load is in accordance with the load rate during a compressor demand load cycle 100%, 75%, 50%, 25% phase jump change, and their respective probability factors are A, B, C, D; 4) Assume that the engine always operates at 75 % to 100 during a compressor demand load cycle Within the % output power range, the engine's rated output power matches the maximum required load of the refrigeration system.
According to the above assumption, the thermal efficiency ηh of the hybrid gas heat pump system to the compressor delivery power is ηh = {β+η12η2η3η4(1 -β) }η5(1) The thermal efficiency ηc of the conventional gas heat pump system to the compressor delivery power is ηc = Η11 A +η12 B +η13 C +η14 D(2) Formula (1), (2) η11, η12, η13, η14 are the thermal efficiencies of the engine output load of 100%, 75%, 50%, 25%, respectively; β is the ratio of the power directly delivered by the engine to the compressor to the total compressor power; η2 is the efficiency of the AC/DC converter of the inverter; η3 is the generator efficiency; η4 is the motor efficiency; η5 is the power synthesis device and the compressor Axis efficiency between.
2 Simulation results and analysis 2.1 Parameter selection In the HPGHP system, η2 is taken as 0. 85, η3 is taken as 0. 9 , η4 is taken as 0. 9 , η5 is taken as 0. 98. Engine load rate is 100%, 75%, 50% The thermal efficiency at 25% is 0.38, 0.36, 0.32, 0. 28.
2. 2 Calculation Results Analysis To compare the performance of the GHP system and the HPGHP system, it is only necessary to compare the thermal efficiencies of the two heat pumps to power the compressor. It can be seen that when the probability factors A, B, C, D are constant, the β value has a critical value β0, when β = β0, ηh = ηc, and when ββ0, ηh > ηc. It is shown that in the HPGHP system, when β is above a certain critical value, the thermal efficiency ηh of the HPGHP system is higher than the thermal efficiency ηc of the GHP system.
The relationship of change (A = 0. 25, B = 0. 25, C = 0. 25, D = 0. 25) indicates that the critical value β0 varies with the values ​​of the probability factors A, B, C, D. The larger the value of A and B is, the larger the critical value β0 is. It indicates that in the HPGHP system, when the compressor power high load operation condition is dominant, β should be relatively large, otherwise the thermal efficiency ηh of HPGHP system will be lower than that of GHP system. The thermal efficiency ηc; conversely, when the compressor power low load operating conditions account for the majority, when β takes a small value (that is, when the battery pack delivers a larger proportion of the compressor's power to the compressor's total required power), It is possible to make the thermal efficiency ηh of the HPGHP system higher than the thermal efficiency ηc of the GHP system.
In summary with the change of different partial load probability factors and β, in order to improve the thermal efficiency of the power system in the hybrid gas heat pump air conditioning system, the key problem to be solved is the dynamic load matching between the power synthesis device and the refrigeration system compressor. Effective energy management of battery pack and gas engine power is an effective way to solve the problem. The battery pack capacity is not only related to the power system, but also related to the heat pump air conditioning load, the initial investment of the system, and the heat loss of the battery pack. How to determine the matching between the battery pack capacity and the engine power is an issue that needs to be studied in depth.
3 Conclusions 3.1 In the HPGHP system, reasonable and effective energy management of the state of charge SOC and engine output of the battery pack is an effective way to obtain the best fuel economy of the whole system.
3. In the HPGHP system, the ratio of the power directly delivered by the engine to the compressor and the power of the entire compressor is one of the key factors affecting the thermal efficiency of the powertrain. Only when this ratio is above a certain threshold, the power of the HPGHP system The thermal efficiency of the system is higher than that of the conventional GHP system.
3. In the HPGHP system, when the compressor demand power and low load operating conditions account for the majority, the battery pack increases the power delivered by the compressor within a certain proportional range, which can ensure that the thermal efficiency of the HPGHP system is higher than that of the HPGHP system. The power system of the GHP system.
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