A novel run-around membrane energy exchanger (RAMEE) system is designed, built, and tested for heating, ventilating, and air-conditioning applications. The RAMEE system consists of two counter-cross-flow liquid-to-air membrane energy exchangers, one located in the supply and the other in the exhaust air streams of a building. Inside each exchanger, a micro-porous membrane separates the air and desiccant solution streams. This membrane allows heat and water vapor exchange between the two streams. The RAMEE system thus exchanges sensible and latent energy between the supply and exhaust air streams by using a desiccant solution as the energy carrier that is pumped in a loop between the two exchangers. The RAMEE performance is evaluated by testing the system with various air and desiccant solution flow rates during standard summer and winter operating conditions. During summer test conditions, the total system effectiveness increases with increasing desiccant flow rate, but decreases as the air flow rate increases. Under winter test conditions, the total effectiveness changes little with changes in the air and desiccant flow rates. For some test conditions, the maximum total effectiveness of the system is between 50 and 55%. The effectiveness data are compared to available correlations and reasons for discrepancies are discussed. (C) 2010 Elsevier B.V. All rights reserved.