A method of controlling the temperature of a thermal load within a structure (50), including providing a structural member (10) which has a high thermal mass, the temperature of the thermal load being controlled by permitting thermal energy transfer between the structural member (10) and the thermal load, the method including providing the structural member (10) with at least one duct (18) for receiving a supply of air, and an outlet (26) for enabling the supply of air to flow from the duct (18) to the thermal load, so as to enable convective thermal energy transfer between the air passed along the duct (18) and the thermal load, wherein the thermal energy transfer between the air passed along the duct (18) and the thermal load is controlled by adjusting the temperature of the air passed along the duct (18), the method further including providing a conduit (32) for carrying thermal energy transfer fluid in the duct (18), the conduit (32) being in thermal contact with the duct (18) of the structural member (10) and the air passing through the duct (18).