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We are currently facing a global climate crisis, which demands that we decrease our energy consumption and carbon footprint. An essential area of focus is the energy optimization of buildings. Purpose: The objective of this study was to assess the current indoor climate within the office building Vråken in Västerås and investigate different measures for the ventilation system and identify potential energy and cost savings. Method: A literature review was carried out to establish the theoretical foundation and examine previous research in the subject area. The staff's perception of the indoor climate within the office building was evaluated through a survey. Relevant information was collected to understand the building's construction and current ventilation system. Further on, a model of the office building was established in IDA ICE to simulate the two selected ventilation measures. Finally, a life cycle cost calculation compared the profitability of the studied measures. Results: The results indicate that the measures have a minor impact on the indoor climate compared to the reference case. Assessing the changes in the indoor climate is challenging due to multiple climate parameters and the simulation results of this study are considered uncertain. The results show that the energy consumption of ventilation can be reduced by 46 or 51%. This corresponds to an annual energy savings of either 122 or 110 MWh, depending on the chosen measure. The first measure, which involves installing zone dampers on each floor, has an estimated investment cost of 92 531 SEK. The second measure, which entails equipping one of the floors with a separate air handling unit, is estimated to cost 388 650 SEK. The profitability assessment shows that the reduction in the total life cycle cost is 2 683 332 SEK for the first measure and 2 631 543 SEK for the second measure. In total, both measures result in a cost savings of 45 or 44% over a period of 25 years compared to the buildings current ventilation system. Conclusions: The results from this study are influenced by several factors with varying degrees of impact, including the existing ventilation system, building model and the assessment of the indoor climate. Despite this, the results indicates that the studied measures can maintain an acceptable indoor climate and at the same time save both energy and costs for the ventilation in the office building.