An environmental control system comprising: a comfort unit (100, 400, 400a-c, 802a-d, 900, 910, 920, 940) constructed to create a thermal microenvironment (614, 614a-b) around one or more users (300, 612, 612a-b), the thermal microenvironment having a temperature different from that of an environment surrounding the microenvironment, the comfort unit comprising: a thermal regulation module that heats or cools air for the thermal microenvironment; and an air delivery module that directs the heated or cooled air to the one or more users to create the thermal microenvironment, wherein the thermal regulation module includes a heat exchanger (118, 408, 408a-b, 450, 946) and a thermal storage material (TSM) (122, 406, 406a-c, 812a-f, 922, 954) thermally coupled to the heat exchanger, the TSM is constructed to store heat therein, and the thermal regulation module is configured as a vapor compression system (VCS) , characterised in that : the environmental control system is configured to operate the VCS to provide onboard generation during certain times to recharge the TSM such that: in a first mode of operation, to cool the air for the thermal microenvironment, the heat exchanger is a condenser of the VCS and the VCS operates to store waste heat from the condenser in the TSM, the TSM changing temperature and/or phase to store the waste heat therein, and in a second mode of operation, to recharge the TSM, the VCS operates as a thermosiphon such that heat stored in the TSM is released via the heat exchanger of the VCS, thereby recharging the TSM. a thermal regulation module that heats or cools air for the thermal microenvironment; and an air delivery module that directs the heated or cooled air to the one or more users to create the thermal microenvironment, wherein the thermal regulation module includes a heat exchanger (118, 408, 408a-b, 450, 946) and a thermal storage material (TSM) (122, 406, 406a-c, 812a-f, 922, 954) thermally coupled to the heat exchanger, the TSM is constructed to store heat therein, and the thermal regulation module is configured as a vapor compression system (VCS) , characterised in that : the environmental control system is configured to operate the VCS to provide onboard generation during certain times to recharge the TSM such that: in a first mode of operation, to cool the air for the thermal microenvironment, the heat exchanger is a condenser of the VCS and the VCS operates to store waste heat from the condenser in the TSM, the TSM changing temperature and/or phase to store the waste heat therein, and in a second mode of operation, to recharge the TSM, the VCS operates as a thermosiphon such that heat stored in the TSM is released via the heat exchanger of the VCS, thereby recharging the TSM. in a first mode of operation, to cool the air for the thermal microenvironment, the heat exchanger is a condenser of the VCS and the VCS operates to store waste heat from the condenser in the TSM, the TSM changing temperature and/or phase to store the waste heat therein, and in a second mode of operation, to recharge the TSM, the VCS operates as a thermosiphon such that heat stored in the TSM is released via the heat exchanger of the VCS, thereby recharging the TSM. <EOS>