This assignment is realised as a part of the collaborative project Sustainable Energy and Environment in Western Balkans that aims to develop and establish five new internationally recognized MSc study programs for the field of Sustainable Energy and Environment , one at each of the five collaborating universities in three different WB countries. The project is funded through the Norwegian Programme in Higher Education, Research and Development in the Western Balkans, Programme 3: Energy Sector (HERD Energy) for the period 2011-2013.In this paper, a low-energy office building in Norway has been analyzed. The case building is located in Trondheim at the address Professor Brochs gate 2, as shown in Figure 1. The building is rented as an office building to nineteen different companies. This master thesis aims to define the possibilities for use of the condenser heat in building by analyzing a cooling plant which provides both heating and cooling to the building at the same time.The paper explains the optimization of the heat pump, responsible for the cooling of rooms in the building. The optimization is used for defining the parameter values which give the greatest energy saving and, besides that, their mutual influence has been shown in the optimization process, as well as the influence of the parameters to the energy saving