Impact of ductwork airtightness and conduction losses on heat recovery efficiency

We have developed a simple model to estimate ductwork leakage and heat conduction losses in steady-state conditions for a balanced ventilation system. Implemented in a spreadsheet, it allows us to calculate their impact on heat recovery efficiency consistently with EN 15241 without the need for a dynamic simulation tool. One case study shows that the global heat recovery of a balanced ventilation system with a nominal heat recovery of 80% can be reduced to less than 50% if the ductwork leakage and thermal resistance are poor. These large energy impacts and today’s field data suggest that these aspects should be considered in energy performance calculations and that building professionals will have to pay particular attention to duct leakage and thermal resistance with the trend towards nearly zero-energy buildings.