The study presented in this paper originated from observations made regarding the thermal conditions during winter in highly insulated dwellings with mechanical ventilation with heat recovery (MVHR). Previous observations indicate an oversupply of heat to bedrooms and a successive extensive window ventilation, which leads to an increased space-heating demand.
Detailed simulations were conducted to explain the causes for the observed thermal conditions and to elaborate improved solutions for heating and ventilation during winter. Various MVHR solutions and control strategies, as well as building design solutions, were investigated regarding their impact on the thermal conditions in bedrooms and on the space-heating demand.
The results clearly illustrates that the supply-air temperature and the temperatures in the living room and bathroom have substantial effects on the thermal conditions in the bedrooms. A one-zone MVHR solution, with approximately the same the supply-air temperature to all rooms, has clear limitations regarding the provision of thermal comfort in bedrooms.
The clear potential of a two-zone MVHR solution, where the supply-air temperature to the bedrooms is controlled independently from other rooms, was observed. With a two-zone MVHR solution, the thermal conditions in bedrooms can be improved and the space-heating demand can be reduced.
This paper presents an analysis of how the design of a photovoltaic (PV) system influences the greenhouse gas emission balance in a net zero emission building (nZEB). In a zero emission building, the emissions associated both with the energy required in the operation of the building (operational emissions) and the energy used to produce the building materials (embodied emissions) are offset by renewable energy generated on-site (avoided emissions). The analysis is applied to a nZEB concept for a single-family building, developed by the Norwegian Research Centre on Zero Emission Buildings. Previous analyses have shown that the installation of a PV system accounts for a significant share of the embodied emissions of a nZEB. The objective of this paper is to assess how the PV system design choices influence the embodied and avoided emissions, in order to determine how the environmental impact can be minimised. Four different PV technologies (Si-mono, poly-Si and CIS, and high-efficiency Si-mono) in four different system designs for flat roofs are evaluated using two different grid emission factors. The installations are compared by means of net avoided emissions, greenhouse gas payback time (GPBT), greenhouse gas return on investment (GROI), and finally the net emission balance of the building. The results show that the system with the largest area of high-efficiency Si-mono modules achieves the best lifetime emission balance, but that the greenhouse gas return on investment is highest for the optimally oriented CIS modules.
The net-zero emissions building (nZEB) performance is investigated for building operation and embodied emissions in materials for Norway’s cold climate. An nZEB concept for new residential buildings was developed in order to understand the balance and implications between operational and embodied emissions over the building’s life. The main drivers for the CO2 equivalent (CO2eq) emissions were revealed for the building concept through a detailed emissions calculation.
Previous investigations showed that the criterion for zero emissions in operation is easily reached by the nZEB concept (independent of the CO2eq factor considered). Nevertheless, embodied emissions from materials appeared significant compared to operational emissions. It was found that an overall emissions balance, including both operational and embodied energy, is difficult to reach and would be unobtainable in a scenario of low carbon electricity from the grid i.e. low CO2eq factor for electricity. In order to make these conclusions robust, a sensitivity analysis was performed on the dominant sources of CO2eq emissions, as well as, on how it impacts the emission balance during the building lifetime. In the baseline work, embodied emissions were evaluated using the EcoInvent database in order to get a consistent life cycle assessment (LCA) method for all the building materials. The first step of this sensitivity analysis is therefore performed to compare embodied emissions when specific Norwegian Environmental Product Declarations (EPD) were used instead of generic data from EcoInvent thus making data more representative for the Norwegian context. In addition, the photovoltaic (PV) system, which supplies renewable electricity to the building, also contributes significantly to the embodied emissions. The second step of the analysis evaluates different PV system design options in order to find the one with highest net emissions reduction. Finally, since the building concept was based on a highly-insulated building envelope, the dominant source of emissions during building operation turned out to be electric appliances. The third step of the analysis thus discusses the energy consumption of electric appliances and how it could be reduced through more efficient products, especially the so-called hot-fed machines (i.e. washing machines, tumble dryer and dishwasher).
Co-publication with StableWood
In highly-insulated buildings such as passive houses, the space-heating distribution subsystem can be simplified by reducing the number of heat emitters. In this context, the bi-directional flow through open doorways is known to be an efficient process to support the heat distribution between rooms. This process is therefore investigated using field measurements within a Norwegian passive house. The so-called large opening approximation proves to model fairly the mass flow rate, but also the convective heat transfer if the thermal stratification is accounted for. Furthermore, the discharge coefficient appears to be independent of the heater type and location in the room.
New and refurbished buildings have to relate to ever increasing standards regarding energy efficiency and energy consumption. This results in well insulated building envelopes with low air leakages offering reduced heating demands. One of the downsides of this is that these buildings are easily warmed up to such a degree that in order to sustain an acceptable indoor climate, removal of excess heat becomes a necessity. The removal of surplus heat is often done through means of mechanical cooling. However, energy consumption related to mechanical cooling is considered incompatible with achieving zero energy buildings (ZEB). As a response, the use of Ventilative cooling (VC) solutions is settling, and it is by many considered crucial in realizing ZEB. Ventilative cooling refers to the use of ventilation air in order to reduce or eliminate the need for mechanical cooling. VC can be applied through both mechanical and natural ventilation strategies, as well as a combination. To achieve efficient VC while ensuring an acceptable thermal climate, the first step is to include measures that provide minimization of heat gains.
This paper examines the application of ventilative cooling solutions in cold climates through simulations of an already existing kindergarten in Norway. This kindergarten has a mixed-mode ventilation system integrating mechanically balanced ventilation with natural ventilation from motor controlled windows. In this paper this kindergarten has been analyzed by means of energy use and thermal comfort with IDA ICE program. The validated simulation of the kindergarten has been compared to simulations of the same kindergarten using DCV and VAV (both without cooling) and hybrid window ventilation and exhaust fan and only window controlled natural ventilation(these two last with night set back allowed). Results show important energy savings when using ventilative cooling as outcome of the low outdoor temperatures and the same applies for night cooling. Simulation results indicate that solutions like hybrid could cut the annual energy consumption by as much as 13 % compared to conventional mechanical ventilation. When looking at the thermal environment and indoor temperatures, it is found that for really warm days, it is hard to sustain acceptable temperatures without the use of night set back or mechanical cooling otherwise. Ventilative cooling is proven to be relevant to highly occupied buildings and will be crucial to achieving energy targets for renovated or new zero energy buildings while the indoor climate is maintained.