Latent heat thermal energy storage tanks, where carbon fiber brushes are inserted to improve the heat transfer rates in the phase change materials, arc installed in an air conditioning system of a building as a space heating resource. The measured outlet fluid temperatures are compared with the numerical ones predicted by a previously developed three dimensional heat transfer model. The preliminary numerical results had unallowable prediction errors, which probably resulted from poor contact between the brushes and the heat transfer tubes due to an installation problem of the brushes. However, the numerical results predicted by a corrected model agree well with the experimental ones under various operating conditions. The effect of the brushes on the thermal outputs of the tanks is then investigated using the corrected model. The result shows that the brushes contribute to saving space and reducing the cost of the tanks. (c) 2005 Elsevier Ltd. All rights reserved.