Dynamic analysis of the low-temperature district network "Suurstoffi" through monitoring

The Lucerne University of Applied Sciences has been analysing and monitoring the low- temperature district heating and cooling network (LTN) “Suurstoffi” since 2012. The analysis showed that heating demand was twice as high as expected. On the other hand, waste heat from free cooling was much lower than expected. The higher heating demand and the lower heat recovery combined resulted in a negative energy balance and hence in an average temperature decrease of the ground storage over the last two years. First of all, a pellet oven was installed as an interim solution in order to supply additional heat to the LTN. Secondly, direct electric heating was used to support the domestic hot water production in order to reduce the energy demand out of the LTN. These temporary measures were only set up until the first part of the planned hybrid solar panels (PVT) were taken into operation in summer 2014. The upcoming data of the monitored summer 2015 will help taking the decision if the temporary measures have to be extended and if additional PVT panels need to be installed. So far, the measured electricity demand to operate the LTN and the connected heat pumps was more than twice as high as expected. This is mainly due to the high electricity demand for temporary electrical heating for domestic hot water, circulation pumps and heat pumps. Thanks to the monitoring, hydraulic shortcoming, which caused the high electrical consumption of the circulation pumps, could be identified. The heat pumps consumed more electricity than planned due to the excess space heating demand and domestic hot water of the consumers. If, in addition to the electricity demand for the heat pumps, the electricity demand of the circulation pumps is taken into account, the overall network efficiency (yearly COP measured = 4.6) is lower than expected (yearly COP planned = 6.8). As a result of the monitoring analysis over the last two years, the following outputs and outcomes could be provided:

The real efficiency of the thermal network has been calculated and benchmarked
Design mistakes have been identified and guidelines for planning have been developed
The energy efficiency has been improved by optimizing the system operation
The accuracy of the monitoring has been improved
The influence of the user on the energy efficiency has been quantified.

The real efficiency of the thermal network has been calculated and benchmarked
Design mistakes have been identified and guidelines for planning have been developed
The energy efficiency has been improved by optimizing the system operation
The accuracy of the monitoring has been improved
The influence of the user on the energy efficiency has been quantified.

Energy integration of CO2 networks and Power to Gas for emerging energy autonomous cities in Europe

Luc Girardin, François Maréchal, Raluca-Ancuta Suciu

The concept of urban CO2 networks has been developed to deploy heat pump based district heating and cooling systems in dense urban areas. The use of the CO2 phase change reduces the cost of the heat distribution while allowing to recover waste heat that is typically rejected to the environment. The use of heat pumps to harvest heat from the environment and to supply heat to buildings allows one to propose district systems with COP as high as 6. Heat pumps can use the electricity produced by photovoltaics already providing up to 60 % of the total consumption. This paper studies the integration of fuel cell based power to gas for the seasonal storage of the excess electricity produced in the summer by PV panels. The methane stored in liquid form is used in the winter to balance the electrical needs by fuel cell based co-generation, making therefore the city 100% supplied by renewable energy. The present work evaluates the integration of CO2 district energy network including power to gas systems on a compact urban block considering heating, cooling, electricity, e-mobility and waste management for different European climatic zones. In order to reach fully autonomous blocks using solar PV and municipal and industrial waste heat, a PV area of 10 to 35 m2/cap would be needed. The rooftop area available appears to be sufficient in areas like Southern Europe, while more area or alternative renewable sources such as wind or hydro are needed for other climatic zones. Regarding the economic feasibility of the system, the results show that an investment of 900 to 1300 euro/cap would be needed, with a payback time between 11 and 14 years, depending on the different climate zones in Europe.

2018

Key Energy and Technological Aspects of Three Innovative Concepts of District Energy Networks

Patrick Chatelan, Daniel Favrat, Samuel Henchoz, François Maréchal

Energy needs in urban areas are heterogeneous by their nature, spatial distribution and temperature level required. Three concepts of district energy networks that could provide the energy services efficiently to a city centre are compared. The focus is on the energy and technological aspects. These networks are characterized by similar temperature levels; between 9.5 °C and 18 °C, rely on free cooling for most of the cooling services and use a combination of centralized and decentralized heat pumps to provide the heating services. Two of these concepts exploit the latent heat of evaporation/condensation of CO2 and of the refrigerant R1234yf to store and transfer heat. The third concept is more conventional and uses the sensible heat of liquid water, however with a small temperature spread. The proposed networks allow the waste heat emitted by the users requiring cooling to be transferred and valourised by the users requiring heating, thus reducing the load on the central plant. For the area considered, where the annual heating and cooling demand are 53.1 GWh and 49.4 GWh respectively, the annual electricity required to supply the thermal services amounts to 10.87 GWh for CO2, 10.52 GWh for water and 9.60 GWh for R1234yf. © 2016 Elsevier Ltd. All rights reserved.

2016

Integration of Organic Rankine Cycles for Waste Heat Recovery in Industrial Processes

Matthias Bendig

Developing a methodology that allows identifying maximumelectricity production with the help of Organic Rankine Cycles (ORC) from the waste heat of an industrial process, at the lowest specific cost, without jeopardising the increase of the industrial process’s thermal efficiency. Such is the goal of this thesis. In order to reach this goal, a software tool which is able to identify the most suitable cycle for a heat source regarding electricity production and cost efficiency is developed and explained in detail. Threemain areas of research can be identified, the definition of waste heat, the analysis of experimental data with the help of data reconciliation and the identification of a suitable working fluid and operation parameters of an ORC for any given heat source. A method for identifying, characterising and quantifying the available waste heat, which can be converted into a useful form, for any industrial system, is presented. A distinction is made between avoidable and unavoidable waste heat. Combined pinch analysis and exergy analysis is used to characterise the waste heat potential of a given process. Based on the study of two industrial processes, it will become clear how the constraints of a waste heat analysis influence the outcome and the potential for the integration of ORCs. The studies illustrate how the increase in energy efficiency and degree of heat recovery and integration of a process can be contradictory to the production of electricity with ORCs. The concept of data reconciliation is needed for the measurements, collected from two ORC demonstrators. Apart from "classical" data reconciliation, a new method is presented, which consists in including parameters as virtual measurements and time dependency of measurements. This increases the redundancy of the system and thus the overall accuracy of the reconciled values. A methodology, capable of choosing the designpoint, a suitable working fluid and a cycle configuration, for the lowest specific investment cost while at the same time maximising the electricity output, for a given process environment is developed. The new methodology uses a multi objective optimisation (master optimisation) andMixed Integer Linear Programming (MILP) problem (slave optimisation). A novel approach of combining multi objective nonlinear master optimisations with single objective linear slave optimisations is introduced, increasing the reliability of the algorithm.

EPFL2015

Integration of Organic Rankine Cycles for Waste Heat Recovery in Industrial Processes

Matthias Bendig

EPFL2015