This paper describes a short term thermal energy storage (TES) unit based on an enclosed phase change material (PCM) in polyethylene film bag. As a storage medium, paraffin wax (RII-56) was used. The paper presents experiment results, which include charge, discharge and pressure drop characteristics of the tested unit. The total enthalpy storage in the module depends on the PCM temperature change and ranges from 240 to 262 kJ/kg. The investigations data show that the PCM RII-56 can be successfully used in heat storage applications. (c) 2006 Elsevier Ltd. All rights reserved.