Ductwork design flaws and poor airtightness: a case study about a ventilation system reconditioning in a sealed building

In a sealed building with tight facades, conditions for a good indoor air quality and comfortable conditions must be guaranteed all the time especially for employees. This paper deals with the case of a specific retrofitted building without any openings that immediately shows many difficulties to maintain good indoor air quality in some parts of the occupied volume. An assessment of ductwork and HVAC system performance was first realized, conducted by the SNIA (National Airport Engineering Service). This analysis enabled to explain both the poor performance of the ventilation system observed by facility managers at the building scale, and the local Indoor Air Quality (IAQ) discomfort mentioned by occupants. 
This paper presents the method and results based on an experimental approach with measurements (pressure and airflow rate in the ductwork, airtightness testing of the ductwork), calculation of pressure drops, and observations (duct and internal envelope leakages search, airflow pattern) in order to identify the causes of the current ventilation dysfunction. 
The diagnosis showed that the major problem was due to the poor performance of two supply ventilation ducts (leakages and pressure drops) called A & B, with impact on the fan blowing pressure and on pressure along ducts. Reconditioning measures were proposed by SNIA, including the near-full replacement of ventilation ductwork A and its Air Handling Unit (AHU - 2200 m3/h), the use of a duct sealing solution for ventilation ductwork B and the installation of a fan speed controller on its AHU (1900 m3/h). 
This paper also illustrates the results based on commissioning period after the 2017 upgrading to check all the installation with duct pressure test, airtightness testing, airflow measurements, electric power input for fans and sound pressure level.