Abstract

This thesis project features an energy survey at Vallbacksskolan, a multipurpose educational facility comprised of two joint buildings located in the city of Gävle, in eastern Sweden. This kind of research has gained remarkable interest during the last decade given the continuously increasing energy prices and the global need of turning to a more sustainable energy model. The study at Vallbacksskolan was particularly interesting given the existing prompt refurbishment plans for the building, from which a more efficient construction that is more respectful towards the environment is to be obtained.

The first part of the research has focused on portraying the actual state of thermal energy at the facilities by establishing an energy balance and quantifying the different input and output flows via various calculation methods inside the energy transmission area of knowledge. Such study has shown that energy purchased from the local district heating grid, of around 1085 MWh/year, represents around 50% of the total input to Vallbacksskolan, while free heating sources like solar radiation through the windows and internal generation mechanisms are responsible for the remaining half. Regarding the outputs, transmission losses have resulted to be the highest contributors with 1323 MWh per year that represent 63% of the total. Amongst such losses, walls have been spotted to have the highest outward flow with annually 555 MWh; however, windows have been concluded to be the weakest link given their highest heat flow density of more than 0,31 MWh/m², so it has been stated that they should be one of the pivotal points of any future refurbishment. As far as the remaining output mechanisms are concerned, mechanical ventilation has resulted to contribute with more than 600 MWh for 29% of the total losses, while natural ventilation and hot tap water sum up for the remaining 8%.

The second part of the thesis work has dealt with providing different ways of improving system efficiency at Vallbacksskolan, along with a feasibility and economic effect analysis for each of them. It has been concluded that the most effective measure decreasing indoor temperature settings in order to reduce transmission and ventilation heat losses, which would save the building an estimate annual 96 MWh and 75.000 SEK at no significant investment. The installation of additional glazing in the windows has been considered as the second best option, saving nearly 75 MWh every year with an economic positive effect of more than 4000 SEK/year, given the required investment. The design of a solar collector system for covering hot tap water needs has been given third degree priority, helping prevent the expense of more than 3.500 SEK every year. Finally, a full window renewal has also been proposed but it has turned out to be unprofitable, mainly due to the fact of dealing with a protected heritage building that must preserve its original aspect; the previously mentioned additional glazing has proved to be the right choice for this kind of constructions. If all the affordable efficiency measures were to be implemented, over 200 MWh would be saved every year at Vallbacksskolan, resulting in a reduction of the annual energy expense of over 80.000 SEK. However, it has been stated that further technical analysis is recommended before any final decisions are made in this matter given the approximate nature of the study.