The calculation of the performance coefficient of the heat pump system with the load ratio can also obtain the same calculation result from the angle of the different load output of the heat pump system. Set the cooling capacity, heat release and power consumption of the heat pump system at full load to Qc0, Qh0 and W0, respectively. Introducing the cooling load ratio to the heating load ratio Kc, Kh, QcQC0=Kc, QhQh0=Kh according to QcQC0=(n0)m=Kc and QhQh0=(n0)p=Kh, the relationship between the speed ratio and the load ratio is K= K1mc, K=K1ph, that is, the speed ratio is proportional to the power corresponding to the load ratio.
Thus, the ratio of the coefficient of cooling performance coefficient to the coefficient of heating coefficient can be expressed as COPc=Km-Rmc(7a)COPh=Kp-Rph(7b), and the first two derivatives are used to obtain the first derivative of the corresponding load ratio Kc(Kh). COPc|'Kc=(m-Rm)K-Rmc(8a)COPh|'Kh=(p-Rp)K-Rph(8b)3.
The calculation results can be seen that the two calculation results can be seen: when m>R COPc|'K>0, COPc|'KC>0, that is, as K or Kc increases, COPc value increases, and vice versa; For example, when P>R, COPh|'K>0, COPh|'Kh>0, that is, as K or Kh increases, the COPh value also increases, and vice versa.
The indices m, p and R are characterized by the degree of change in cooling capacity, heat supply and compressor power consumption with compressor speed when other factors are constant. The larger their values, the higher the Qc, Qh and W with the speed. The faster the increase.
The above calculations show that: (1) the influence of the heat pump performance coefficient with the compressor revolution ratio and the load ratio is equivalent in effect, that is, the load change can be satisfied by changing the compressor speed, and the speed adjustment ratio is The corresponding exponential relationship of the load ratio changes; (2) The change of the heat pump performance coefficient with the speed ratio depends on the comparison between the compressor power consumption and the cooling capacity (or heat supply) affected by the load change (speed change). During cooling, when the load change (speed change) has a greater effect on the power consumption of the compressor than on the cooling capacity, the heat pump refrigeration performance coefficient decreases during the variable load condition, otherwise it rises. If the two effects are equivalent, the load changes. The effect on the COP value is negligible, as is the case with heating.
Calculation example This article uses a gas engine heat pump as a calculation example. The gas engine heat pump is a compression heat pump that uses a gas-burning internal combustion engine as a driving force. When the load of the gas engine heat pump system changes, the engine and heat pump unit need to be adjusted. The engine drives the compressor through a belt drive and a coupling. Changing the engine speed can change the speed of the compressor, thereby changing the piston displacement of the compressor and completing the capacity adjustment of the heat pump.
According to the experimental curves of the refrigeration capacity, the heat of the condenser and the change of the compressor speed of the compressor in the gas heat pump system, the influence curves and fitting formulas of the evaporation temperature at a certain (11 ° C) are obtained.
The relationship between the cooling capacity, the heat of the condenser and the power consumption of the compressor and the rotational speed. The experimental results show that the indices m and p are slightly smaller than R, although according to the above analysis, the COPc and COPh decrease slightly with the increase of the rotational speed (load). However, since |mR| and |pR| are small, they are all on the order of 0.1. From equations (5) and (7), both COPc and COPh are changed according to a low index, that is, in a larger range. The internal load characteristics remain basically the same; it is also seen that since the indices m and p are almost equal, the load change characteristics of COPc and COPh are the same.
It is assumed that the rotational speed n0 at full load is the maximum rotational speed of 3000 r/min in the test range of 800 to 3000 r/min, and the load ratio Kc (Kh) is taken as 0. 25, 0.5, 0.75 and 1, causing COPc, The relationship between COPh, and. The results of this study are consistent with the conclusions of [4].
The relationship between heating load ratio Kh and COPh value 5 Conclusion Changing the compressor speed is one of the feasible technical solutions for realizing the heat pump variable load. The research shows that the effect of load change on compressor power consumption is slightly greater than the heat pump heating/cooling capacity. Therefore, when the load increases, the COP value of the heat pump decreases, but the decrease is small. The change is gentle over a wide range, which indicates that the system can adjust the energy input and the cold and heat output in real time according to the load requirements in the whole season to achieve the corresponding optimal performance, and achieve the good operation of the variable load of the variable speed adjustment.
Ungrouped,High Quality Ungrouped,Ungrouped Details, CN
KYD Automatic Mask Machine Factory , https://www.kydultrasonic.com