A system for controlling temperature in a passenger compartment of a vehicle, the system comprising: at least one passenger air channel configured to deliver a passenger airflow to the passenger compartment of the vehicle, at least one thermal energy source, at least one heat transfer device connected to the passenger air channel, at least one thermoelectric device, a first fluid circuit configured to circulate coolant to the thermal energy source and the TED, a second fluid circuit separate from the first fluid circuit, the second fluid circuit configured to circulate coolant to the TED and the heat transfer device, at least one bypass circuit configured to connect the thermal energy source to the heat transfer device, at least one actuator configured to cause coolant to circulate in the bypass circuit instead of the first fluid circuit and the second fluid circuit, the system for controlling temperature being characterised in that: the TED is operatively connected to the first fluid circuit and to the second fluid circuit in order to transfer thermal energy between the first fluid circuit and the second fluid circuit when the system is operated in a start up heating mode before it is determined that the thermal energy source is ready to provide heat to the passenger airflow, and in that at least one control system configured to operate the at least one actuator when it is determined that the thermal energy source is ready to provide heat to the passenger airflow, thereby causing coolant to circulate in the bypass circuit instead of in the first fluid circuit and the second fluid circuit. at least one passenger air channel configured to deliver a passenger airflow to the passenger compartment of the vehicle, at least one thermal energy source, at least one heat transfer device connected to the passenger air channel, at least one thermoelectric device, a first fluid circuit configured to circulate coolant to the thermal energy source and the TED, a second fluid circuit separate from the first fluid circuit, the second fluid circuit configured to circulate coolant to the TED and the heat transfer device, at least one bypass circuit configured to connect the thermal energy source to the heat transfer device, at least one actuator configured to cause coolant to circulate in the bypass circuit instead of the first fluid circuit and the second fluid circuit, the system for controlling temperature being characterised in that: the TED is operatively connected to the first fluid circuit and to the second fluid circuit in order to transfer thermal energy between the first fluid circuit and the second fluid circuit when the system is operated in a start up heating mode before it is determined that the thermal energy source is ready to provide heat to the passenger airflow, and in that the TED is operatively connected to the first fluid circuit and to the second fluid circuit in order to transfer thermal energy between the first fluid circuit and the second fluid circuit when the system is operated in a start up heating mode before it is determined that the thermal energy source is ready to provide heat to the passenger airflow, and in that at least one control system configured to operate the at least one actuator when it is determined that the thermal energy source is ready to provide heat to the passenger airflow, thereby causing coolant to circulate in the bypass circuit instead of in the first fluid circuit and the second fluid circuit.