Currently, most vehicles use waste heat to warm the cabin. Hybrid and electric vehicles (xEV) rely on electric elements to provide much of the heat needed to keep the occupants comfortable. These elements draw energy from the battery, which significantly reduces electric drive range.

Delphi’s HPAC minimizes this draw by recovering heat from the electric motors, batteries and power electronics. Since the system also has an air conditioning capability, one single, compact unit can efficiently heat and cool the cabin as required.

The Unitary vapor compression system is driven by an electric compressor. Heat rejected by the liquid condenser is absorbed by the coolant. The hot coolant travels to the heater in the HVAC module for cabin heating. It can also be directed to the battery pack if it requires heating. The low temperature coolant is directed to the inverter and drive motor where it can scavenge additional heat. There is also the potential to scavenge heat from the cabin air exiting by incorporating a recovery heat exchanger at the body relief valve.

In cooling mode, the cold coolant from the chiller goes to the cooler in the HVAC module for cabin cooling. It can also be directed to the battery pack, inverter, and drive motor for cooling. Waste heat within the system is rejected by the low temperature radiator.

Heating mode. Click to enlarge.		Cooling mode. Click to enlarge.

This strategy, Delphi notes, is quite different from that used in current plug-in hybrid vehicles. In ambient conditions below 0°C, vehicles that generate little combustion heat, such as PHEVs, rely on electric or Positive Temperature Coefficient (PTC) heaters to provide adequate cabin heating and demisting. By not being as dependent on these heat sources, HPAC reduces the energy required for its operation.

Fitting Delphi’s Unitary HPAC to such a vehicle could significantly reduce the energy needed for heating in very cold conditions. Testing has shown that the reduced energy draw from the battery pack could increase the electric drive range by up to 10 percent at low-mid ambient temperatures.

—James Bertrand, president, Delphi Thermal Systems

Rig tests on a plug-in hybrid vehicle system have also demonstrated a reduction in CO₂ emissions equivalent to 3.8 grams per mile. The system currently is semi-hermetic—the heat exchanger joints are hermetic while the TXV and compressor joints are not. This system would have approximately 3.0 grams/year of refrigerant emissions per SAE J2727, 50% less than the lowest leakage rates of current production vehicles. The next generation of this system will be hermetic—without elastomeric seals at the TXV and compressor.

The high efficiency of the system allows it to be extremely compact. It is also suited to a range of refrigerants, providing flexibility in refrigerant cost and supply. Because the refrigerant circuit is contained entirely within the engine compartment, the refrigerant choice is also less compromised by flammability constraints.

Additionally, Delphi’s HPAC requires only half the refrigerant volume of a conventional system and can be shipped and installed fully-charged. Delphi expects to begin production of HPAC for the 2015 model year.

New A/C evaporator for stop-start vehicles. Delphi is also bringing to production a new Phase Change Material (PCM) Evaporator to keep the cabin of start-stop vehicles cooler longer. The system, which is a direct replacement for the original air-conditioning evaporator, will also extend the electric range of hybrid/electric vehicles.

Delphi’s system integrates a reservoir of PCM within the air-conditioning evaporator. During normal operation, thermal energy is removed from the material which solidifies or freezes. When the air conditioning system is stopped, the PCM gradually liquefies or melts, drawing heat from the air to keep passengers cool and comfortable. The system can typically maintain target air temperature at the cabin vents for one to two minutes—depending on the volume of PCM specified—keeping occupants comfortable throughout periods of stop-start driving.

Several families of materials possess phase change properties, including hydrated salts, organic and inorganic eutectic mixtures, paraffins and fatty acids. Delphi selected paraffin-based PCMs for their combination of thermal properties and robust, long-term reliability.

Extensive analysis has enabled Delphi to use the PCM in current evaporators with few additional parts to create a thermosiphon effect with the refrigerant already present within the evaporator, eliminating any moving parts and simplifying the installation.

This technology is now moving from testing to its first vehicle development program and is expected on the road by 2015.

Resources

• Kowsky, C., Wolfe, E., Leitzel, L. and Oddi, F., (2012) Unitary HPAC System, SAE Int. J. Passeng. Cars - Mech. Syst. 5(2) doi: 10.4271/2012-01-1050