Small capacity absorption systems for cooling and power with a scroll expander and ammonia based working fluids

Up to now, the use of ammonia/water absorption cycles has been mainly limited to the production of refrigeration or air conditioning but due to the relatively high generator pressure some authors have proposed the integration in parallel of an expander to produce cooling and power simultaneously. This feature could provide many benefits in the future such as the use of solar thermal energy to partially cover the heating, cooling and electricity demand of a building. In the other hand the life cycle cost of the absorption system is improved because of the increase in the number of running hours in periods in which there is no demand for cooling but the demand for electrical power is still important. This paper shows a new combined absorption system using a scroll expander and three different working fluids using ammonia as refrigerant: ammonia/water, ammonia/lithium nitrate and ammonia/sodium thiocyanate. The scroll expander performance maps were obtained experimentally and modeled to predict the power production, rotational speed and exhaust temperature of the expander and included in the complete absorption cycle model build using Engineering Equation Solver (EES) Software. This system produces different amounts of cooling and power at the desired power/cooling ratio to cover varying demand profiles.