TVOC concentrations measured in Belgium dwellings and their potential for DCV control

Over the last decade, TVOC sensors have been touted as an interesting alternative to CO2 and RH sensors in DCV systems. Nevertheless, there is little evidence on the nature and the profile of TVOC concentrations in modern dwellings.
In this project, metal oxide TVOC sensors were installed in the local exhaust ducts in 3-4 bedroom low energy social housing dwellings equipped with a DCV exhaust ventilation system in Belgium. The TVOC and CO2 concentrations as well as RH levels were measured during operation and 2 control strategies were compared: the DCV was controlled based on the measured CO2 concentration for 2 weeks and subsequently, the same system was controlled based on the TVOC concentration.
From the observed concentrations, it is shown that, due to occupant activities such as cooking, bathing and cleaning, high, short peaks in TVOC concentrations are a typical feature of residential IAQ. This makes TVOC concentration an especially useful parameter for ‘event’ related or purge ventilation control. Nevertheless, the relative frequency of these peaks also raises the question whether it is necessary to raise ventilation rates in response to such normal instances such as eating an orange. The average ventilation flow rate during TVOC control is about 50% larger and the system operates at a higher flow rate compared to the CO2 control 40% of the time on average.
A further observation is that there is only a very weak correlation between the TVOC concentration and the CO2 concentration at lower concentrations, most likely due to faster secondary reactions of the TVOC compared to the virtually inert CO2. This limits the use of TVOC as a control parameter for non-purge related events.
In conclusion, highly peaked TVOC concentrations were observed in low energy dwellings, demonstrating the use of TVOC sensors as a control parameter for purge ventilation in DCV systems.