Vapour-compression heat pumps that use absorption technology with two-stage and three-stage solution circuits are investigated by simulation. Ammonia-water is the working fluid. The cycle performance is evaluated for high-temperature-lift applications. The applications include three cooling cases, four heating cases, and a combination of cooling and heating. The two- and three-stage cycle performance is compared with that of the vapour-compression cascade cycle and the single-stage vapour absorption cycle. For the combined cooling and heating case (a temperature lift of about 172degC (310degF)) and the heating cases, the single-stage cycle is seen to operate at supercritical pressures (i.e., at pressure between the critical pressures of ammonia and water). The two- and three-stage cycles operate below the critical pressure of ammonia and at significantly lower pressure ratios. With a view to improving the coefficient of performance (COP), certain modifications are introduced in the configuration of the cycles. These include passing the vapour from the lowest temperature desorber into and through the next higher temperature desorber instead of mixing separate vapour streams. Similarly, the compressed vapour is absorbed in subsequent absorbers instead of splitting the discharge vapour stream. These changes reduce the irreversibilities associated with the internal heat transfer processes in the cycle and thereby improve the COP. The cooling COP of the two-stage cycle is found to improve by about 27%, while that of the three-stage cycle improves by more than three times as compared with the original versions of these cycles.

KEYWORDS: year 1996, calculating, heat pumps, dual source heat pumps, absorption refrigeration, vapour compression heat pumps, cyclic, ammonia, water, temperature lift, high temperature, cooling, heating, performance, comparing, performance, cascade refrigeration, coefficient of performance, heat flow