AstraZeneca is one of the largest biopharmaceutical companies in the world, and one of the facilities they have is located in Gärtuna, Södertälje. The facility itself is very big with a floor area of 560.000m2 and has a complex energy system. Caverion holds a facility management contract at AstraZenca, hence operates some of the energy system. The energy investigation of this thesis is part of the work of Caverion to ensure a sustainable energy system in Gärtuna. The energy investigation will include mapping of the energy distribution, seeking for potential of improvements and carry out suggestions for energy optimizations. The methods used during the investigation was a literature study, interviews with personnel of both Caverion and AstraZenca, study of the energy system and calculations relevant to the field of study. The mapping of the energy system includes the heat, steam and cooling distribution. When the mapping of the system was done it was clear that the areas with most potential for improvements were the steam and cooling distribution.The mapping of the steam distribution shows a loss of nearly 46% of the steam at year 2014 and the corresponding cost of about 13,640,000 SEK. Even though the steam distribution showed great potential for improvements, it was found that the work of investigating the system would be too difficult for the scope of the thesis. The cooling distribution however is more accessible and the potential is still high due to low coefficient of performance. Two suggestions for energy optimizations were carried out. The first suggestions involves upgraded electric fan motors for some of the cooling towers, and the second suggestion is to modify existing dry coolers in benefit to utilize free cooling during winter period. The fan motor upgrade based on calculations is estimated to result in a yearly energy saving of at least 1526 MWh and a corresponding cost saving of at least 800,000 SEK per year after the pay-off time (9 months). The dry cooler modification based on calculations is estimated to result in a yearly energy saving of 3053 MWh and a yearly cost saving of 2,083,449 SEK after the pay-off period of 5 months. The investigation carried out in this thesis is relevant to both Caverion and AstraZeneca as it points out the areas with potential of improvements and also gives suggestions on energy optimizations that will reduce energy consumption and result in energy cost savings.