Impact of ventilation non conformities: calculation methodology and on-site examples

Energy efficient buildings are getting more and more airtight to avoid thermal losses through uncontrolled air leakage and rely more and more on mechanical ventilation to ensure a good indoor air quality. In practice ventilation systems are however not always perfectly installed, and several problems are often encountered on-site. 
In France the new environmental regulation for new buildings RE2020 now includes a mandatory inspection of ventilation systems for non-residential buildings.  
This study is part of an on-going French research project PromevenTertiaire aiming at improving the reliability of inspection of ventilation systems protocols in non-residential buildings. A survey addressed to various professionals of this sector allowed to identify 5 particular non-conformities that are both often encountered in existing ventilation systems and which can rather easily be quantified. This paper presents the calculation methodology to evaluate the impacts, from simple on-site measurements, of 4 of these non-conformities: filter clogging; inadequate fans settings; non-insulated duct sections and inadequate AHU scheduling. Another paper specifically details the calculation methodology for leaky ductwork [1]. 
On-site inspections of ventilation systems were performed on three non-residential buildings: two secondary schools located in two different French climatic zones and one office building. The data and visual observation collected were used to quantify the extra costs related to each of these non-conformities encountered in one of the buildings. This allows to give practical examples and orders of magnitude in order to raise awareness on these issues and their consequences.   
In particular, it is estimated that an AHU of 13 500 m3/h with a leaky ductwork (2.5 class A) induces yearly thermal losses of 815 kWh (122€) and a fan overconsumption of 2281 kWh (342€); that the fan overconsumption due to filter clogging is higher from the second year of use than the price of a new filter; and that in an office equipped with two 2.5kW AHU a ventilation not switched off at night and not regulated with sensors induces respectively a yearly overconsumption of 22100 kWh (3315€) and 8424 kWh (1263€).