A concept of a hybrid adsorption cooling unit for vaccine storage utilizing solar energy as a main power supply and a gas burner as an alternative power supply has been developed. The components of the cooling unit have been designed to work under the weathering conditions of Burkina Faso, West coast of Africa according to the requirements of the World Health Organization. For the first adsorber, which is driven by a gas burner, zeolite-13X has been selected. For the second adsorber to be driven by solar energy selective water sorbent SWS-2L has been applied. Water is selected as a refrigerant for both adsorbents. Theoretical investigations of the expected performance of the designed cooling unit have shown a coefficient of performance (COP) of 0.28 for the solar-operated sy,stem based on the heat input to the adsorption unit, at the design conditions of T-evap = -5 degrees C, T-con = 55 degrees C, T-ads = 38 degrees C, T-des(max) = 122 degrees C. For the gas-heated system, also a COP of 0.28 has been estimated at the design conditions of T-evap = -5 degrees C, T-con = 55 degrees C, T-ads = 38 degrees C, T-des(max) = 280 degrees C. The variations of COP, cooling capacity and the heating power required to operate both systems have been estimated for a broad range of desorption temperatures. It turns out that the SWS-2L/water system is much more sensitive to the operating conditions than the zeolite-13X/water system. The obtained results should serve in designing both control and heating components of the cooling unit. (c) 2006 Elsevier Ltd. All rights reserved.