Preliminary Measurements of the Energy Impact of Infiltration in a Test Cell

Abstract

All existing computer models for calculating energy consumption of buildings assume that infiltration increases the heating and cooling load on a building by an amount equal to the mass flow rate of the infiltration times the enthalpy difference between the inside and outside air - with the latent portion of the enthalpy difference sometimes neglected. Recent theoretical and empirical evidence suggests that this approach sometimes, and perhaps often, overstates the energy cost of infiltration. Calorimetric measurements have been conducted on a small test cell with measured amounts of infiltration introduced under conditions: a) where the existing model is expected to give correct results; and b) where the existing model is expected to overstate the energy cost of infiltration significantly. The preliminary data obtained convincingly show that infiltration can lead to a much smaller change in the energy load than is customarily calculated; changes as small as 10 per cent of the calculated value have been measured in a test call. The data also suggest that the phenomenon occurs in full-sized houses as well. This leads us to introduce the infiltration Heat Exchange Effectiveness (IHEE) as a measure of the effectiveness of a building in 'recovering' heat otherwise lost (or gained) due to infiltration. Preliminary investigation of possible correlations between the pressure coefficient determined from fan pressurization data and the infiltration heat exchange effectiveness factor suggest that the fan pressurization results may be useful in predicting the infiltration heat exchange effectiveness factor for buildings.