The aim of the thesis was to plan a more energy efficient way to execute ventila-tion for two business areas which have different opening hours, and to count the refund of the change. These business areas are located in a shopping mall in Seinäjoki and the same air conditioning unit TK/PK 57 serve them both. The challenge of the work was that the current ventilation was not planned to serve the stores with current serving times and space divisions. Also old documents for the ventilation changes were or missing or not updated.