Steady-state heat transfer in an insulated, reinforced concrete wall: theory, numerical simulations, and experiments

In this paper, we focus on the steady-state heat transfer in an in situ con structed, insulated, reinforced concrete wall. The wall consists of two rei nforced concrete slabs that sandwich an insulation layer. The two halves of the wall are joined by a series of steel wires to provide the needed struc tural integrity but unavoidably act as thermal shunts that increase the hea t transfer rate. Nonetheless, the thermal performance of the wall surpasses that for an uninsulated wall because of the presence of the insulation. We compare the heat transfer rates predicted by a three-dimensional, numerica l model with laboratory test data. The results from these data, and from nu merous sensitivity studies performed with the model, show that the steady-s tate heat transfer in the wall may be approximated by the isothermal planes model. A more accurate estimate is obtained by a weighted average of the i sothermal planes result and a simple parallel path model in which the isoth ermal-planes result is weighted by the factor 0.85. An appropriate value of the weighting factor, specific to a particular wall panel configuration, m ay be obtained using a correlation and graphical results that are presented in the paper. These quantitative results for the steady-state panel conduc tance are expected to be useful in exploring manufacturing strategies that would improve the thermal resistance of the panel, in designing energy-cons erving buildings that employ such panels, and in establishing accurate ener gy standards and energy code compliance methods. (C) 1999 Elsevier Science S.A. All rights reserved.