Infiltration Heat Recovery in Residential Buildings

Air infiltrating (left side) and exfiltrating (right side) through cracks in the insulated walls of a room. (Click here to see a recent conference paper (in PDF format) on this work.)

The purpose of this work is to determine the energy impact of air leakage through the external envelope of residential buildings. The traditional means of predicting this effect is to merely add another term in the energy balance to account for air infiltration. The conduction heat loss remains the same as for the case without infiltration, and the infiltration heat loss is represented as the product of the mass flow rate of infiltrating air, its heat capacity, and the temperature difference between inside and outside.

In reality, there is heat transfer between the infiltrating air and the wall. Infiltrating air is warmed by heat conducting through the wall from the warm interior to the cold exterior. Because infiltrating air flows into the room, it is said that the air "recovers" some of the heat lost by conduction. This process changes the thermal profile in the wall and the temperature of the air entering the room from infiltration. This results in different values for the conduction, infiltration, and total heat losses than are predicted by the traditional method. A similar effect is seen in the exfiltration process where warm air leaks from inside to outside.

This study is being performed via computational fluid dynamics (CFD) simulations with the commercial software FLUENT. Initial results are being compared with experimental data for validation. Further studies with different geometric designs under several environmental conditions are underway to provide heat recovery data for a variety of general situations. This CFD data is being used to develop a simplified mathematical model for prediction of infiltration heat recovery in buildings.

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Last Modified: June 27, 2000