A heat pump includes a refrigerant loop. The refrigerant loop includes a first heat exchanger, a first region of a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a compressor, a vapor generator, an accumulator, a first expansion valve, and a first three-way valve. The compressor includes a low-pressure inlet, a mid-pressure inlet, and an outlet. The vapor generator is positioned downstream of the outlet of the compressor and upstream of both the low-pressure inlet and the mid-pressure inlet. The vapor generator includes a first region and a second region. The accumulator is positioned immediately upstream of the compressor. The accumulator includes an inlet and an outlet. The first expansion valve is positioned upstream of the accumulator. The first expansion valve includes an inlet and an outlet. The first three-way valve is positioned immediately downstream of the first expansion. valve and immediately upstream of the accumulator.