Enhancement of a double-effect absorption cooling system using a vapor recompression absorber

Abstract

One of the limitations of aqueous lithium bromide (LiBr/Water) single-effect absorption chillers is their inherently low COP and their inability to take advantage of the availability of high temperature heat to achieve higher COPs. Recent efforts to develop triple or even quadruple-effect absorption chillers appear unlikely to find adequate support in the current deregulated utility marketplace because of their first-cost premiums, corrosion problems associated with high temperature operation, and an oversize footprint. Double-effect cycles, on the other hand, are beginning to capture a significant portion of the heat activated cooling marketplace. This study investigates the effect of adding a Vapor Recompression Absorber (VRA) to a double-effect machine. The VRA, which can be retrofitted into an existing or constructed as part of a new double-effect absorption chiller, is an adiabatic component and uses heat released by condensation to evaporate more refrigerant. This causes an increase in the refrigerant flow rate in the refrigerant circuit, increasing the cooling capacity of the system. Hence, a system utilizing a VRA can achieve higher COPs. This paper presents methods to mathematically characterize the VRA and numerical simulations of a double-effect absorption system employing the VRA unit. The performance enhancement is investigated and the benefits in terms of improving COP and capacity are documented. Also, the impact of design parameters is documented.