Abstract

The research center of Zero Emissions Buildings (ZEB) has a goal of eliminating the greenhouse gas emissions associated with all phases of building development and use. This is achieved through more sustainable building construction and more efficient energy use. The Norwegian government has a similar goal of achieving zero energy buildings as a standard by 2020. This has led to proper investigation in technological solutions that can help to achieve these goals. In a net-ZEB perspective, combined heat and power (CHP) is considered as a potential energy supply solution for buildings. CHP is seen as an emerging technology which has the potential to reduce primary energy consumption and the associated greenhouse gas emissions. This is achieved through concurrent production of electricity and heat using the same fuel. However, since the thermal output of CHP is substantially larger than the electrical output, the potential offered by CHP systems depend on their suitable integration with the thermal demand of the building. In this thesis, a simulation model is used to investigate the performance of a CHP system compared to a conventional gas boiler system in a multi-family building that complies with the Norwegian building norm, TEK10. Different operational strategies are applied to the CHP model to investigate its optimal integration in domestic dwellings. Analyzing the simulation results indicates that the CHP system gives primary energy savings in all operational strategies, but operating the system in follow thermal mode represents the greatest savings. Applying load management resulted in further savings, and the fuel efficiency did increase, achieving a value of 75.1% on a higher heating value (HHV) basis. The CHP device is more capable of covering the electricity demand as peaks are shaved. This implies that CHP is better suited for buildings with stable electricity and heat demand. Electric demand following operation did however result in poorer primary energy savings and the corresponding CHP efficiency did decrease due to poorer heat recovery efficiency and frequent part load operation. Using renewable upgraded biogas as fuel in thermal following mode did result in the highest primary energy savings. Primary energy consumption was reduced by 34.3%, and the corresponding system efficiency based on primary energy was 70.7% on a HHV basis. From an environmental perspective, it has been found that the CHP system is more favorable when the CO2-emission factor for electricity is high. This is due to the reduction in electricity imports from the grid, and the part substituted electricity covered by the electricity exports from the CHP system. The greatest reduction in grid imports was seen when the CHP-device was set to follow the electrical demand of the building without restriction in thermal surplus. The CHP was able to cover 88.27% of the electricity demand, but the system efficiency decreased as significant amounts of heat was wasted due to overproduction. The highest amount of exports was seen when load management was implemented in thermal demand following mode, and represented 76.61% of the produced electricity. Using the current CO2-emission factor for the UCPTE electricity mix, a reduction in CO2 emissions was seen for all CHP configurations. The use of renewable fuel resulted in the greatest savings, and emissions were reduced by 71.91% compared to the gas boiler, representing a tremendous reduction. The use of natural gas as fuel resulted in significantly lower savings. The best case achieved a 26.58% reduction compared to the reference system. When using the net-ZEB definition, only CHP fuelled on renewable fuel did achieve CO2-savings. This questions the environmental viability of today’s CHP systems as the CO2-emission factor for electricity is expected to decrease over the coming years due to an expected increase in use of renewable fuels. Further research should therefore be done in order to enable an efficient CHP technology based on renewable fuels. This will decrease the emissions significantly, making CHP more competitive.

The building enclosure plays a relevant role in the management of the energy flows in buildings and in the exploitation of the solar energy at building scale. An optimized configuration of the façade can contribute to reduce the total energy demand of the building. Traditionally, the search for the optimal façade configuration is obtained by analyzing the heating demand and/or the cooling demand only, while the implication of the façade configuration on the energy demand for artificial lighting is often not considered, especially during the first stage of the design process. A global approach (i.e. including heating, cooling and artificial lighting energy demand) is instead necessary to reduce the total energy need of the building. When considering the total energy use in building, the optimization of a façade configuration becomes not straightforward, because non-linear relationships often occur. The paper presents a methodology and the results of the search of the optimal transparent percentage of a façade module for office buildings. The investigation is carried out for the four main orientations, on three "average" office buildings (with different surface-area-to-volume ratio), and with different HVAC system's efficiency, located in Frankfurt. The results show that the optimal configuration, regardless of the orientations and the surface-area-to-volume ratio, is achieved in an "average" office building when the transparent component of the façade module is between 35% and 45% of the total façade module surface. The north-exposed façade is the one that presents the highest difference between the "optimal configuration" and the worst one, while the south-exposed façade is the one which suffers less in case of the "worst" configuration.

Abstract

The paper presents a case study of an office building with a façade integrated PV system in Norway. Due to the urban surrounding the PV system is subject to significant overshadowing. The aim is to optimize the solar energy potential of the building in order to propose improved alternatives to the current system applying a multi-level simulation approach. The first level is performed to calculate the maximum solar potential on the building envelope in an unobstructed scenario. The second level examines the shading effect on the building in its urban context. The analyses allow localizing the areas of the building with the highest solar potential. In the third level, the energy output of different solar technologies (solar thermal and PV) is evaluated. The results demonstrate that the solar potential analysis in the early stage is important for choosing the most performing system.

The building enclosure plays a relevant role in the management of the energy flows in buildings and in the exploitation of solar energy at a building scale. An optimized configuration of the façade can contribute to reduce the total energy demand of the building.

Traditionally, the search for the optimal façade configuration is obtained by analyzing the heating demand and/or the cooling demand only, while the implication of the façade configuration on artificial lighting energy demand is often not addressed.

A comprehensive approach (i.e. including heating, cooling and artificial lighting energy demand) is instead necessary to reduce the total energy need of the building and the optimization of the façade configuration becomes no longer straightforward, because non-linear relationships are often disclosed.

The paper presents a methodology and the results of the search for the optimal transparent percentage in a façade module for low energy office buildings. The investigation is carried out in a temperate oceanic climate, on the four main orientations, on three versions of the office building and with different HVAC system’s efficiency. The results show that, regardless of the orientations and of the façade area of the building, the optimal configuration is achieved when the transparent percentage is between 35% and 45% of the total façade module area. The highest difference between the optimal configuration and the worst one occurs in the north-exposed façade, while the south-exposed façade is the one that shows the smallest difference between the optimal and the worst configuration.