Design architecture and performance analysis of automotive heat pump systems

In this case, the energy cost of the HP ATA architecture is slightly lower than that of ATW (ΔΕ ~-3%) at the same battery charging speed.

The changes in the average cell temperature and coolant temperature are shown in Figure 9: It can be seen that there is no difference in the temperature characteristics of ATA and ATW.

Figure 7 Example of current curve for fast charging of electric vehicle battery

Figure 8 Battery heat release and chiller cooling power changes during rapid charging of pure electric vehicle batteries

Figure 9. Changes in battery and coolant temperature during simulated battery fast charging. There is no difference between ATW and ATW in terms of coolant and battery temperature behavior.

Cabin and battery cooling

In the cabin and battery cooling configuration, the HP ATA architecture performs slightly better than ATW (ΔE ~ -4%, see Figure 11). With the same cabin and battery performance, ATA proves to be the most energy-efficient solution, as shown in Figure 10.

Cabin heating

In the cabin heating configuration, the HP ATA architecture consumes less energy than the ATW, as shown in Figure 11.

As the ambient temperature increases, the following changes can be observed:

The energy consumption of HV-HTR is zero when the ambient temperature is 0℃;

HV-PTC reduces energy consumption;

The relative energy consumption of E-CMP increases: the absolute contribution increases before 5°C and then decreases, because when the ambient temperature T＞5°C, the HV PTC is in the OFF state.

Figure 10 Cabin and battery cooling In terms of COP and energy consumption, the ATA architecture performs slightly better than the ATW

Figure 11 Comparison of cabin heating ATA and ATW shows that ATA has lower energy costs in terms of total energy consumption. The figure also reports the percentage contribution of each component to the total energy consumption.

When the exhaust temperature reaches the target, E-CMP starts to adjust to absorb less energy.

When the ambient temperature T＞0℃, the energy absorption of E-CMP overcomes the energy consumption of the electric heater.

The energy contribution of fans and blowers does not change in absolute conditions because they operate at maximum power.

Furthermore, due to the lack of a coolant loop, in the HP ATA architecture, the cabin heats up faster than in the ATW due to the additional intermediate CBN HTR heat exchange efficiency of the ATW (Figure 12).

Finally, consider the variation of the HP system COP in Figure 13 with increasing ambient temperature: the system COP increases due to the reduced cabin heating demand.

Figure 12 Cabin heating. The air temperature curve at the cabin exhaust port shows that the ATA structure can achieve faster and higher cabin air temperature.

Figure 13 Cabin heating. As the ambient temperature increases, the cabin heating demand decreases and the range of both systems increases. The COP evolution of the ATA architecture at different ambient temperatures is slightly higher than that of the ATW architecture.

The COP of the ATA system is higher than that of ATW, so ATA is definitely more energy-efficient.

The COP difference between the two architectures is getting bigger and bigger.

Battery heating

In the battery heating configuration, the control strategy of the thermal management system aims to achieve and maintain the maximum temperature difference between the coolant and the battery throughout the simulation. The purpose of this control is to avoid the possibility of too high a temperature difference, which may cause premature battery aging due to thermal stress phenomena and/or thermal expansion.

In this case, the HP ATW system architecture consumes less energy than the ATA architecture to a large extent (Figure 14). In fact, in the ATW architecture, the action of the HP reduces the activation of the HV HTR; the HV HTR and the HP initially work at maximum power to reach the maximum ΔT between the cell and the battery as quickly as possible, and then the HV HTR starts to adjust to maintain the ΔT.

In the proposed ATA architecture, only the coolant HV HTR works to heat the battery, so it works at maximum power to achieve the target ΔT of the cell-to-battery. Therefore, the huge difference in energy consumption between ATW and ATA in this case is related to the HV HTR, which in ATA runs more than the HV HTR in ATW to achieve the same effect, absorbing more power and releasing less heat energy (efficiency < l) to the coolant. < p="" style="margin: 0px; padding: 0px;">

As the ambient temperature increases:

The total power absorption is reduced for both architectures;

In ATW, due to the shorter integration time, the absolute contributions of CMP and HV HTR decrease, while the relative contribution of CMP increases and the contribution of HV HTR decreases.

Figure 14 Battery heating. Comparison of ATA and ATW shows that ATW has lower energy costs in terms of total energy consumption. The percentage contribution of the individual components to the total energy consumption is also reported in this figure.

Figure 15 Battery heating. The average temperature change of the battery during the simulation shows that the battery heating speed is faster in the ATW architecture than in the ATA architecture.

Another interesting result is that the maximum ΔT of the cell-battery is reached faster in ATW than in ATA (Figure 15). In fact, the simultaneous action of HP and HV HTR at maximum power ensures more heat energy to the coolant than the action of HV HTR at maximum power alone in the case of ATA. Therefore, the battery heats up faster in ATW than in ATA.

Cabin and battery heating

In cabin and battery heating modes, ATW performs slightly better than ATA at ambient temperatures up to 5°C.

At Tamb = 10°C, the operation of both systems switches to cabin heating mode, so ATA is more effective than ATW.

Fig. 16 Cabin and battery heating. The comparison between ATW and ATW shows that the total energy consumption is lower for ATW within 5°C of ambient temperature. The percentage contribution of each component to the total energy consumption is also reported in the figure.

At the same outlet temperature, as the ambient temperature increases

Reduced total power consumption

The absolute contribution of HV HTR is constant before 0°C (it always works at maximum power, increasing its relative contribution), then decreases (it works in regulation), and finally becomes zero at Tamb = 10°C.

HV PTC contribution decreases

E-CMP contribution increased

In ATW architecture, additional HV HTR consumption for preheating the coolant at Tamb - 0°C.

In addition, as the ambient temperature increases (Figure 17):

System COP increases due to reduced heating demand;

In the range of Tamb = 5℃, the COP of the ATA system is lower than that of ATW; then at Tamb = 10℃, ATA is more efficient than ATW because battery heating is not required and both architectures operate only in cabin heating mode.

ATW is more efficient than ATA architecture only when battery heating is required.

The COP value also includes the heat exchange efficiency at:

Heating fluid and panels (convection heat transfer)

Electric plates and cells (conduction heat transfer)

For this reason, the efficiency values ​​are lower than expected for an analysis limited to the heating fluid.

Figure 17 Cabin and battery heating. The variation of system COP at different ambient temperatures shows that ATW is more effective than ATA only when battery heating is required. For comparison, the COP of a standard thermal management system without HP is shown.

Cabin dehumidification

In cabin dehumidification mode, the HP ATA architecture consumes less energy than ATW because in this case no coolant pump is running and the cabin air is heated directly by the ACond without the additional inefficient coolant CBN HTR.

Therefore, in this case, the HP system is more efficient for the ATA architecture. At the same outlet temperature of about 50°C, as the ambient temperature decreases:

The EL energy consumption was reduced for each configuration.

E-CMP contribution reduction (CMP in the regulations)

Fig. 18 Cabin dehumidification. The comparison between ATA and ATW shows that ATW has lower energy costs in terms of total energy consumption, and the percentage contribution of each component to the total energy consumption is also reported in the figure.

Figure 19 Cabin dehumidification. The change in the air temperature curve at the cabin outlet shows that the ATA architecture can reach a faster and higher in-vehicle air temperature.

The absolute contribution of PTC decreases due to lower cabin heating demand.

The contribution of the electric fan and the air conditioning blower remains constant in absolute terms but increases in percentage due to maximum power operation.

A positive effect of the lack of a coolant loop in the ATA is that the exhaust temperature target is reached more quickly (Figure 19); the rate of temperature increase increases with increasing ambient temperature.

WHR cabin heating from batteries

In cabin heating mode using battery waste heat recovery, the ATA architecture heats the cabin faster than the ATW due to the absence of an intermediate coolant loop (Figure 20).

Figure 20 Cabin heating with WHR. The cabin vent air temperature curve shows that the ATA architecture can reach faster and higher air temperatures in the cabin.

Fig. 21 Cabin heating with WHR. Comparison of ATA and ATW shows that ATA has slightly lower energy costs in terms of total energy consumption. The percentage contribution of each component to the total energy consumption is also reported in the figure.

At Tamb = 10°C and the same cabin vent temperature, ATA absorbs less electrical energy than ATW; compared to ATW configuration, E-CMP absorbs more energy due to the higher refrigerant pressure, but the energy contribution of high-pressure PTC to air heating in the ATA heat pump system is much lower.