ECOS: Integrated and practical energy planning for new districts

In this paper, we propose a unified method for the integrated energy planning during the development of new districts for all involved actors. Taking energy related problems such as equipment choice and size, costs and environmental impact early into consideration avoids confronting engineers later on with difficult to resolve problems. We provide a method that has been proven during the bidding process of the Metamorphose project in Lausanne. During the planning of new districts, different stakeholders such as politicians, architects or urban plan- ners are involved in the definition of the requirements. Each actor has its own set of methods with its specialized tools to assure reaching his goals. Bringing the actors together and integrating their tools into the decision process from the beginning on helps finding a sustainable solution and economizes time for each actor. Based on the initial demand of the City of Lausanne, the following set of indicators is used: • operation and investment costs, • primary energy: renewable and fossil fuel usage, • greenhouse gas emissions and • exergy efficiency. A dynamic building simulation software, CitySim, defines the energy demand and estimates the solar irradiation on the roof tops. This demand is converted into a composite curve using EnerGIS. Applying process integration techniques identifies the best equipment size and type which will then be used to calculate the different indicators. The City of Lausanne defined the square meters to be constructed for each category. In addition to the private program with big multi-story dwellings and office buildings, the city included a public program with an Olympic swimming pool and a football stadium. Our proposed method considers both programs and evaluated systematically each proposal based on the criteria mentioned in the bidding process. Compared to the last public bidding process during the metamorphose project, this time, the winner was scored among the top scored proposals in the energy field. Besides energy, the jury used other criteria such as mobility and architectural design to identify their winner. Using expertise from different laboratories at EPFL, the City of Lausanne was able to consider a com- plex set of indicators to identify their winner.

Novel models towards predictive control of advanced building systems and occupant comfort in buildings

Nikolaos Zarkadis

People in developed countries spend today most of their time inside buildings as part of the modern way of life. As a result, the building sector accounts for almost 40% of the total energy consumption and a big part of the energy bill goes to maintain the visual and thermal comfort of their occupants. At the same time, awareness is being raised during the last decades about the greenhouse gas emissions and the possibly irreversible effects of global warming; both linked to excessive use of non-renewable primary energy sources which still power most of the world, including our buildings. Thus, moderating the energy consumed in them is a top priority. However, this does not imply a horizontal cut in energy consumption that would result in a drop of user comfort. Instead, we suggest that improving energy efficiency in buildings while maintaining or even improving the user comfort is the optimal solution. It is indeed the core of this thesis that there is a great energy saving potential in refining the control of building systems such as electric lighting, heating, cooling and ventilation, which more than often consume a lot of energy without delivering the analogous amount of visual and thermal comfort. In this direction, this thesis proposes the development of a novel predictive control algorithm for the control of electrochromic glazing using a low cost sky scanner using a simple web camera. The developed algorithm demonstrated an average prediction accuracy of 92% and integrates and controls the blinds and electric lighting to maximise visual comfort taking into account outdoor and indoor conditions, presence and user actions. Measurements and extensive simulations showed that the elaborated algorithm improves thermal and visual comfort when compared to standard glazing coupled with blinds and exhibits acceptable levels of energy consumption for space heating and electric lighting. In the same subject of improving building control, a novel approach for controlling building systems by using state-based stochastic data-driven models to identify "season" is defined and developed. We reason that the season variable is unique to every building and it depends on weather conditions, user behaviour and building construction. The developed models identified "season" with an accuracy that ranged from 69 to 91% and it was shown through simulations that a controller based on Hidden Markov Models can reduce energy demand for heating and improve the thermal comfort of occupants in different building construction types. Finally, the use of Hidden Markov Models was further explored in this thesis by suggesting a novel model for the estimation of occupants' visual comfort in buildings. The proposed model is based on horizontal workplane illuminance measurements using ceiling-mounted sensors as well on vertical illuminance monitoring at the observer's eyes plane (pupillary illuminance) by means of wearable portable sensors. We argue that the proposed model improves greatly over the various existing discomfort glare indices and metrics and it is also convincingly demonstrated that it can be seamlessly integrated and used in building automation systems based on fuzzy logic.

EPFL2015

Potential of refrigerant based district heating and cooling networks

Samuel Henchoz

Urban areas represent an ever increasing challenge in terms of energy use and environmental impact associated with it. Projections from the United Nation expect this number to reach 66% by 2050. In Europe 40% of the final energy consumption and 36% of the emissions of greenhouse gases are caused by buildings. The building sector is also one of the area where there is a great potential of reduction of the greenhouse gases emissions and of the dependence on fossil fuels. Among the measures that can help realise this potential, efficient energy conversion technologies supplying thermal energy services could play an important role. The present thesis aims at demonstrating the potential of a new type of district network, capable of delivering indistinctly cooling and heating services using a two-pipe network and in which the transfer of energy across the network is done by exploiting the evaporation/condensation of a refrigerant. The main research question is: "Is it possible to build and operate safe, reliable, energy efficient and economically profitable district heating and cooling networks that use a refrigerant as a transfer fluid?" The demonstration followsthree axes, the first being a thermoeconomic analysis. Thisanalysis focuses on a test case area in Genevaâs city centre where 5 variants of refrigerant based district heating and cooling networks, one cold water network and the mix of conversion technologies currently in use are compared on the basis of their energy and exergy performances and on the economic profitability. Considerations on economic uncertainty, safety and technical issues are also included in the analysis. The key findings are: â¢ All the variants of network can potentially reduce the final energy consumption of over 80% as compared to the current situation. â¢ All the variants of network have rather similar exergy efficiencies comprised between 39.5% and 45%. â¢ The most profitable variant uses CO2 as a transfer fluid and an open cycle CO2 heat pump at the central plant. It costs initially between 27 and 35 mio â¬ , reaches break-even in 4 to 6 years and the net present value after 40 years is comprised between 40 and 80 mio â¬. â¢ A cold water network is the second best option, although more expensive initially and thus less profitable, it has several advantages in terms of safety and availability of components. â¢ The CO2 variants exhibit a much better compactness than the cold water network. The second axis is the design, construction and testing of a lab scale refrigerant network. First a description of the design process and of the test facility is provided. It is followed by a presentation of the results of the test campaign. The tests aimed at demonstrating the practical feasibility of the concept, mostly by assessing the controllability of the network. Overall the good behaviour of the test facility and its ability to be smoothly and automatically controlled could be demonstrated, which further improved confidence in the practicality of the concept. The third axis is the development of dynamic models of simulation. These models are described in the present manuscript. They include, heat exchangers, pipes, pumps and valves. A short comparison between experimental and simulation results is also provided. The comparison between experiment and simulation showed that at their current stage of development the models cannot simulate accurately enough a refrigerant based network.

EPFL2016

Exergy assessment of future energy transition scenarios with application to Switzerland

Matteo Allais, Victor Codina Gironès, Daniel Favrat, François Maréchal, François Richard Vuille

Using an exergy based indicator is highly desirable to compare future national energy strategies. A new web- based information platform called energyscope.ch, informing the general public on the Swiss energy transition was presented at ECOS2016. This paper presents a new extension of the approach that we plan to call exergyscope.ch, clearly stating exergy and distinguishing between primary exergy, final exergy and useful exergy. This allows for a graphical interpretation of the exergy efficiency of each conversion step from primary exergy to final exergy, all the way to useful exergy. Different future energy scenarios for Switzerland are compared to illustrate the gain in exergy efficiency between different strategy choices. Monthly variations in exergy supply are considered by using an average reference temperature for each month. The analysis assesses the useful exergy requirement for all energy services including building and transportation. For heating and cooling services, the proposed framework is coherent with the introduction, reported earlier, of an exergy efficiency indicator in a Law on energy. Accordingly the global exergy efficiency for providing a given useful exergy service can be calculated by multiplying the individual exergy efficiency of each conversion steps. The useful industrial thermal exergy is introduced in a simplified manner with an average service temperature.