Kylsystem i en kontorsbyggnad : Funktionsanalys av ett ventilationssystem i en modern kontorsbyggnad ur energi- och termiskkomfort synpunkt under en sommarperiod

Sammanfattning: In this master thesis, cooling systems are studied in a modern office building in Umeå during a summer period. The project has been done in collaboration with the municipality of Umeå and aims to analyze the cooling system’s task in the building depending on the various systems that makes up the ventilation system. This was done by examining its operation and determining where improvements could be made. The ventilation system is equipped with two types of geo-energy systems for preheating and cooling the outdoor air, Earth to Heat Exchanger (EAHE) and Borehole Heat Exchange (BHE). The ventilation system also includes a thermal wheel and a heat battery that handles the building’s heating demands. In order to get an idea of how these systems contribute to the ventilation system, cooling effects and temperature relationships for each system were investigated. The study showed that the various systems that make up the ventilation system complement each other well to meet the cooling needs during the summer period. The building’s ventilation system contributed to a total temperature reduction of the outdoor air up to 8 ◦C. The BHE system seems to be the one that contributed most to the cooling system with air temperature reduction of 4 ◦C. However, the system was constantly running and contributed to unnecessary cooling of the incoming air. This could have been avoided by programming the system to switch off at specific outdoor temperatures. The air intake that is a part of the EAHE system contributed to high cooling effects in the morning, which corresponds to large temperature reductions of the outdoor air. A conceivable reason may be due to the material property of the air intake. The air intake that is made of steel is cooled by the cold summer nights and has the ability to preserve the cold. When the ventilation system starts operating in the morning, the outdoor air flows through the cooled air intake and leads to large temperature reductions. Contrary to this, when it is hot outside, the air intake can contribute to large temperature increases. This is a concern because the air intake acts primarily as an air filter for the EAHE system and heating the already hot outdoor air before it reaches the ventilation units is not beneficial. To study this, a model of the air intake was built in COMSOL and simulated. The simulation showed that the air intake heats up significantly and leads to uneven temperature distribution through the surface when the outdoor temperature is 28 ◦C and the sun shines straight on the surface. It was also found that the air temperature inside the air intake is affected by the surface temperature. To see if there is a difference with the temperature distribution, the air intake was then simulated with other material types such as brick, wood and PEX. This resulted in the distribution of temperature through the surface becoming more uniform and the air temperature inside the air intake barely being affected by the surface temperature. Therefore, it is recommended to change the material type of the air intake in order to avoid unintended heating of the outdoor air before it reaches the ventilation unit.