Absorption heat pump systems for solution transportation at ambient temperature — STA cycle

This paper proposes an efficient method of energy transportation using an absorption system called “solution transportation absorption system (STA)”. The solution is transported at an ambient temperature so that tube-insulation is not required in the STA system. Absorption cycles using aqueous LiBr and NH3–H2O solutions are compared to the STA applications. A concentration shift to the left occurs in the LiBr–H2O STA system which reduces the crystallization temperature lower than 25°C. A wide range of concentration is obtained in the NH3–H2O STA system which results in a low solution mass flow rate leading to a larger cooling capacity for a given mass flow rate of the solution. In the LiBr–H2O STA system, the overall conductance (UA) has greater effect on the system capacity than it does on the COP. The UA of the rectifier has the most significant effect on the COP and the capacity of the NH3–H2O STA system. The tube diameters of the LiBr–H2O and NH3–H2O STA systems are reduced to six and eight times smaller than that of the conventional chilled water transportation system, respectively. A cooling capacity of 5000 RT can be transported as far as 115 km and 510 km with a tube diameter of 10 cm using LiBr–H2O and NH3–H2O STA systems, respectively. The NH3–H2O system is a better choice than the LiBr–H2O system for the STA applications from the viewpoints of pumping power and the maximum transportation distance.