A split liquid desiccant air conditioning system for heating and humidifying an air stream flowing into a space in a building, the split liquid desiccant air conditioning system comprising: a conditioner located inside the building, said conditioner including a plurality of first structures arranged in a substantially vertical orientation, each structure having at least one surface across which a liquid desiccant can flow, each structure also including a passage through which a heat transfer fluid can flow, wherein the air stream can flow between the structures such that the liquid desiccant humidifies and heats the air stream, the conditioner further comprising a sheet of material positioned proximate to the at least one surface of each structure between the liquid desiccant and the air stream, said sheet of material permitting transfer of water vapor between the liquid desiccant and the air stream; a regenerator located outside the building connected to the conditioner by liquid desiccant pipes for exchanging liquid desiccant with the conditioner, said regenerator including a plurality of second structures arranged in a substantially vertical orientation, each structure having at least one surface across which the liquid desiccant can flow, each structure also including a passage through which a heat transfer fluid can flow, said regenerator causing the liquid desiccant to absorb water from an air stream flowing through the regenerator; an indirect evaporative cooling unit coupled to the conditioner for receiving the heat transfer fluid that has flowed through the first structures and a portion of the air stream that has been humidified and heated by the conditioner, said indirect evaporative cooling unit including a plurality of third structures arranged in a substantially vertical orientation, each structure having at least one surface across which water can flow, each structure also including a passage through which the heat transfer fluid from the conditioner can flow, wherein the air conditioning system is configured so that the portion of the air stream received from the conditioner flows between the structures such that the water vapor is evaporated from the water, resulting in humidification of the air stream, and so that the air stream treated by the indirect evaporative cooling unit is exhausted inside the building; an apparatus for moving the air stream through the conditioner and the indirect evaporative cooling unit; an apparatus for circulating the liquid desiccant through the conditioner and regenerator; an apparatus for circulating heat transfer fluid through the conditioner and the indirect evaporative cooling unit; and a heat source for heating the heat transfer fluid in the conditioner and the indirect evaporative cooling unit. a conditioner located inside the building, said conditioner including a plurality of first structures arranged in a substantially vertical orientation, each structure having at least one surface across which a liquid desiccant can flow, each structure also including a passage through which a heat transfer fluid can flow, wherein the air stream can flow between the structures such that the liquid desiccant humidifies and heats the air stream, the conditioner further comprising a sheet of material positioned proximate to the at least one surface of each structure between the liquid desiccant and the air stream, said sheet of material permitting transfer of water vapor between the liquid desiccant and the air stream; a regenerator located outside the building connected to the conditioner by liquid desiccant pipes for exchanging liquid desiccant with the conditioner, said regenerator including a plurality of second structures arranged in a substantially vertical orientation, each structure having at least one surface across which the liquid desiccant can flow, each structure also including a passage through which a heat transfer fluid can flow, said regenerator causing the liquid desiccant to absorb water from an air stream flowing through the regenerator; an indirect evaporative cooling unit coupled to the conditioner for receiving the heat transfer fluid that has flowed through the first structures and a portion of the air stream that has been humidified and heated by the conditioner, said indirect evaporative cooling unit including a plurality of third structures arranged in a substantially vertical orientation, each structure having at least one surface across which water can flow, each structure also including a passage through which the heat transfer fluid from the conditioner can flow, wherein the air conditioning system is configured so that the portion of the air stream received from the conditioner flows between the structures such that the water vapor is evaporated from the water, resulting in humidification of the air stream, and so that the air stream treated by the indirect evaporative cooling unit is exhausted inside the building; an apparatus for moving the air stream through the conditioner and the indirect evaporative cooling unit; an apparatus for circulating the liquid desiccant through the conditioner and regenerator; an apparatus for circulating heat transfer fluid through the conditioner and the indirect evaporative cooling unit; and a heat source for heating the heat transfer fluid in the conditioner and the indirect evaporative cooling unit.