A transport refrigeration unit, comprising: an engine; a refrigeration cycle comprising: a compressor; a condenser; an expansion valve; an evaporator; first piping configured to fluidly couple an outlet of the compressor and an inlet of the condenser; second piping configured to fluidly couple an outlet of the condenser and an inlet of the expansion valve; third piping configured to fluidly couple an outlet of the expansion valve and an inlet of the evaporator; and fourth piping configured to fluidly couple an outlet of the evaporator and an inlet of the compressor; wherein the transport refrigeration unit further comprises: a fluid loop to produce heated fluid from the engine, the engine configured to drive operations of the compressor; a heat exchanger disposed along the fluid loop and in the refrigeration cycle between the condenser and the expansion valve such that the heated fluid thermally interacts with refrigerant of the refrigeration cycle; and a hot gas bypass valve to control a quantity of the refrigerant removed from the first piping and supplied to the second piping between the condenser and the heat exchanger. an engine; a refrigeration cycle comprising: a compressor; a condenser; an expansion valve; an evaporator; first piping configured to fluidly couple an outlet of the compressor and an inlet of the condenser; second piping configured to fluidly couple an outlet of the condenser and an inlet of the expansion valve; third piping configured to fluidly couple an outlet of the expansion valve and an inlet of the evaporator; and fourth piping configured to fluidly couple an outlet of the evaporator and an inlet of the compressor; a compressor; a condenser; an expansion valve; an evaporator; first piping configured to fluidly couple an outlet of the compressor and an inlet of the condenser; second piping configured to fluidly couple an outlet of the condenser and an inlet of the expansion valve; third piping configured to fluidly couple an outlet of the expansion valve and an inlet of the evaporator; and fourth piping configured to fluidly couple an outlet of the evaporator and an inlet of the compressor; wherein the transport refrigeration unit further comprises: a fluid loop to produce heated fluid from the engine, the engine configured to drive operations of the compressor; a heat exchanger disposed along the fluid loop and in the refrigeration cycle between the condenser and the expansion valve such that the heated fluid thermally interacts with refrigerant of the refrigeration cycle; and a hot gas bypass valve to control a quantity of the refrigerant removed from the first piping and supplied to the second piping between the condenser and the heat exchanger. a fluid loop to produce heated fluid from the engine, the engine configured to drive operations of the compressor; a heat exchanger disposed along the fluid loop and in the refrigeration cycle between the condenser and the expansion valve such that the heated fluid thermally interacts with refrigerant of the refrigeration cycle; and a hot gas bypass valve to control a quantity of the refrigerant removed from the first piping and supplied to the second piping between the condenser and the heat exchanger.