Two advanced valve control configurations were tested, the MSEV with the manufacturer default APID and the MSEV with a cascaded controller (MSEV+CC), as shown in Figure 6.
Significant efficiency gains in the cyclic COP were observed with the use of the MSEV with a default controller (+35%) as compared to the TXVs.
The fast response of the MSEV enables an additional refrigeration migration control strategy to be evaluated.
Because refrigerant migration is assumed to have an effect on start-up efficiency, the MSEV valve is used to evaluate whether the benefits of preventing refrigerant migration outweigh the benefits of the residual cooling achieved in the OFF cycle.
In this case, note that the MSEV offers no discernible improvement compared to the TXV, as its primary means of improving efficiency (i.e., reducing compressor runtime) is not allowed for these tests.
Performance Comparison for Thermostat Controlled Cycling Expansion Valve and Controller Cooling, Cooling, kW tons Thermostatic expansion valve (TXV) 26.2 7.4 MSEV with default controller (MSEV+APID) 34.9 9.9 MSEV with cascade controller (MSEV+CC) 41.2 11.7 Expansion Valve and Controller Power, Power, COP kW tons Thermostatic expansion valve (TXV) 15.1 4.3 1.7 MSEV with default controller (MSEV+APID) 15.3 4.4 2.3 MSEV with cascade controller (MSEV+CC) 15.8 4.5 2.6 Expansion Valve and Controller COP Improvement Thermostatic expansion valve (TXV) -- MSEV with default controller (MSEV+APID) 35% MSEV with cascade controller (MSEV+CC) 53% Table 3.
Figure 4 shows the performance of the designed cascaded controller with MSEVs on a multi-evaporator refrigerant system.
To compare system performance using different control strategies, MSEVs are installed in parallel with the factory -installed TXVs.