NS Reizigers has carried out long-term measurements with provisional CO2-controlled ventilation equipment in two trainsets. The annual savings (assuming a normal Dutch winter) amounted to about 7250 kWh per coach. NS planned to include demand-operated ventilation based on CO2 sensors in one of the refurbishment projects of rolling stock for suburban service. However, the additional investment costs (ca 5000 EURO per coach) specified by the supplier were considered as too high and the feature was not realised.