Compression chillers are a common technology used in district cooling networks, with fluctuating cooling loads and consuming different electricity mixes at different times. This work aims to study these effects on the CFs of operating three compression chillers in a district cooling plant in Austria, using LCA-based CF modelling. Electricity consumption dominates the chillers’ CFs. While using the annual average electricity mix overestimated the CF for two warm-season and mixed-season chillers by 12% and 1%, respectively, it underestimated the CF for a mainly cold season chiller by 6%. Seasonal changes in electricity mixes and cooling loads were well suited to explain the calculated CF deviations and should be accounted for in carbon footprints dominated by renewables-rich electricity consumption.

Tighter legal emission limits require means to prevent releasing harmful substances into the atmosphere during the combustion of biomass. Economic considerations suggest to meet these restrictions by improving the ability to predict and therefore prevent emissions, which can be done by improved control algorithms. This work presents different methods to obtain models for the prediction of carbon monoxide emissions in a small-scale biomass combustion furnace for wooden pellets. The presented models are intended for an application in model based control, either as part of the underlying model or for carbon monoxide soft sensing and fault detection. The main focus is on simple structures which can be handled by the already existing hardware of the furnaces. Different black-box models and a kinetic process model are introduced and compared. The black-box models are based on the measured flue gas oxygen concentration and the combustion temperature, since these measurements are typically available even for smaller plants. The obtained models are validated with measured data in order to find the most suitable structures, of which combined fuzzy black-box models show the most promising results. The presented methodology can be readily applied to the investigated furnace. However, the model parameters have to be adapted for other plants.

In contrast to water-steam Rankine cycles, the ORC process uses organic working fluids. For working fluids of the dry class, a recuperator heat exchanger is frequently installed to increase the cycle efficiency. This paper analyses an improved ORC process with these features: A liquid working fluid stream is injected into the vapour flow between the high-pressure and the medium-pressure stage of the turbine. Furthermore, the recuperator is replaced by a spray condenser. The main objective is to increase efficiency with moderate changes in the process layout. A thermodynamic comparison of the improved process with a state-of-the-art ORC process is carried out by simulations and optimisations. A significant efficiency gain for the improved ORC process is obtained by a combination of the aforementioned features, mainly because of an increase of the mass flow in the economiser of the vapour generator (better heat utilization) and a corresponding mass flow in the medium stage of the turbine (additional power production). As a use case, waste heat utilization from clinker cooler at a temperature level of 275 °C was simulated. The improved process would lead to a significant increase in the overall net efficiency by up to 14%, compared to a state-of-the-art ORC process.

It is in the DNA of district heating (DH) systems that low temperatures are crucial for efficiency, guaranteeing cost competitiveness and integrating alternative heat sources. The general conviction within the DH community is, that reduced temperatures have positive effects for the whole system and economic benefits can be expected. However, there is a lack in evidence-based data to evaluate these effects in monetary terms. The innovative approach of this work is to analyze key characteristics for different technologies by means of energy-economic assessments to show evidence-based energy-related and monetary benefits of reduced system temperatures. The proven benefits should increase the motivation and conviction of utilities and customers in low-temperature systems, both for reducing system temperatures in existing networks and for new networks. The key indicator cost reduction gradient (CRG), introduced in previous work, was applied for the energy-economic assessment of reduced system temperatures. In total, investigations of nine heat generation technologies, the DH network itself and four storage types are presented. The CRGs for the heat generation technologies varies from 0.08 to 0.67 €/(MWh·°C). In the case of alternative heat generation technologies such as heat pumps and solar thermal, a higher sensitivity of the monetary effects compared to traditional heat generation technologies can be observed. Here, higher economic benefits and monetary savings can be expected in future DH networks.

Organic Rankine Cycles (ORC) are a modification of the classical water-steam process and are particularly suitable for electricity generation from low and medium temperature heat sources, e.g., industrial waste heat or geothermal energy. In contrast to the water-steam process, the ORC process uses organic fluids as working fluids. When using working fluids of the dry class (e.g. n-pentane), a recuperator is frequently installed in state-of-the-art ORC processes to increase the cycle efficiency. This paper analyses an improved ORC process design: A liquid working fluid stream is mixed with the vapour flow between the high-pressure stage and the medium-pressure stage of the turbine. Furthermore, the recuperator is replaced by a spray condenser. These two improvements were analysed by thermodynamic process simulations. As a use case, electricity production from clinker cooler waste heat at a temperature level of 275°C was simulated. The improved process as described would lead to an increase in the overall net efficiency up to 14%, compared to a state-of-the-art ORC process.