Carbon fiber cloths are stretched among heat transfer tubes to extend the heat transfer area in latent heat thermal energy storage tanks. The thermal responses of the tanks into which paraffin wax as the thermal energy storage material is packed are experimentally investigated. The experimental results show that the carbon fiber cloths of only 0.4 vol.% improve the heat exchange rate in the tanks. A numerical model describing the heat transfer in the tank well predicts the experimental results. Moreover, the effect of the carbon fiber cloths on the thermal performance for a practical scale tank is numerically discussed. (c) 2007 Elsevier B.V. All rights reserved.