Continuous mechanical ventilation in housing - understanding the gap between intended and actual performance and use.

Improved air tightness and mechanical ventilation systems are regarded as vital elements of low energy strategy in housing. Mechanical ventilation (MV) has become part of the heating energy load optimization model due to its capacity to secure recommended air change levels without depending on daily active control by inhabitants or uncontrolled air leaks. Numerous in-use issues related to continuous mechanical ventilation systems have been identified through field studies. They relate to underperformance of the as built system compared to design targets as well as unintended operation modes. The gap between design intention and actual performance and use of continuous MV in housing context is generally regarded as a threat to expected energy savings or inhabitant's health and as such it should be narrowed as far as possible. Reducing the gap partly depends on the improvement of the continuous MV model to allow for better match with inhabitants needs. This paper proposes a dynamic framework linking factors that influence the emergence of this gap. The framework is based upon findings of previous studies as well as results of a one year-long in-depth Building Performance Evaluation of 40 households in two UK developments. Organizing the pitfalls of embedding MV design into practice in a sequence as well as indicating important links within the process can help to make the complexity more comprehensive and possible to tackle efficiently. Importance of natural ventilation design to backup for MV to increase redundancy and resilience is also highlighted. (C) 2015 The Authors. Published by Elsevier Ltd.