Ursula Eicker

Thermal modelling of a building with an integrated ventilated PV façade

This paper presents a dynamic thermal model based on TRNSYS, for a building with an integrated ventilated PV facade/solar air collector system. The building model developed has been validated against experimental data from a 6.5 m high PV facade on the Mataro Library near Barcelona. Preheating of the ventilation air within the facade is through incident solar radiation heating of the PV elements and subsequent heat transmission to the air within the ventilation gap. The warmed air can be used for building heating in winter. Modelled and measured air temperatures are found to be in good agreement. The heating and cooling loads for the building with and without such a ventilated facade have been calculated and the impact of climatic variations on the performance such buildings has also been investigated. It was found that the cooling loads are marginally higher with the PV facade for all locations considered, whereas the impact of the facade on the heating load depends critically on location.

3D City modeling for urban scale heating energy demand forecasting

An urban energy management tool was developed, which is able to predict the heating energy demand of urban districts and analyze strategies for improving building standards. Building models of different Levels of Detail are investigated and analyzed according to their suitability for forecasting energy demand. Based on the specific 3D city model, an input file is generated, which can be read by the building simulation model. Special focus is put on a method for modeling the heating energy demand of the buildings with the fewest input parameters possible, but one which will give reliable forecast results. A simple transmission heat loss method and an energy-balance method were tested. In both cases, there was a good correlation between the measured and calculated annual values for a case study area of over 700 buildings in Ostfildern, Germany. The results also show that a 3D city model (with low geometrical detail) can be used for energy demand forecasting on an urban scale.

The influence of data quality on urban heating demand modeling using 3D city models

Abstract 3D city models are rich data sets for urban energy analyses, providing geometrical and semantic data required to estimate the energy demand of entire districts, cities and even regions. However, given the diverse availability, uncertainty and Level of Details of these data and the resources required to collect them, managing data quality is a common challenge of urban energy modeling. Knowing the influences of the different input data for different configurations and applications enables to control the result accuracy and recommend intelligent and adequate data collecting strategies, by assigning resources on the most important parameters. This paper investigates the influences of geometrical, meteorological, semantic and occupancy related data quality on the heating demand estimated by the urban energy simulation platform SimStadt, applied to the City of Ludwigsburg in Germany. A focus on a district with consumption data available at building block level allows for a critical comparison between estimated and measured energy demands. Although the quantified information presented in this paper is specific to a case study, the main trends and developed methods are transferrable to other urban energy analysis studies based on 3D city models.

Influence of Condenser Conditions on Organic Rankine Cycle Load Characteristics

A 7 MWth combined heat and power plant (CHP) based on an organic Rankine cycle (ORC) with 5.3 MWth and 1 MWel nominal output is analyzed. A district heating system serves as heat sink; the entire system is heat-led. Two examples for winter and summer operation are shown. The observed characteristics of the condenser are compared to results of a theoretical model. Variable mass flows, temperature levels (72 °C–95 °C) and temperature spreads result in varying condensation temperatures and pressure levels in the condenser (90 mbar to 150 mbar). High mass flows on the secondary side and related low temperature spreads improve the heat transfer and increase the condensation rate in the condenser. The monitoring data support the findings of a steady-state condenser model. As a consequence, advantageous load profiles according to the pressure characteristic of the system can be reached. Live steam pressure, pressure difference across the turbine, and flow rate increase. The effect on the electric efficiency is one percentage point in summer and 1.5 percentage points in winter, which translates to a difference in the electric yield of the cycle of about 10%. Furthermore, the data show that the transient sink conditions cause unsteady operation for the entire cycle.

A method to quantify the energy performance in urban quarters

This study aims to derive an estimating method for the energy performance of urban quarters. To quantify the energy performance of city quarters, the influence of the surrounding urban form must be considered, for instance, the street distance, height of the neighboring buildings, or urban site coverage. In this work, the lighting, heating, and cooling performance of urban districts with different urban forms was simulated in detail using software tools such as EnergyPlus, Radiance, and Daysim. Interrelations between those effects are analyzed with respect to thermal and visual comfort condition. Electric lighting consumption is calculated first, and the thermal effect of artificial lighting is set as an input to the heating and cooling performance calculation. The analyses show that the site thermal performance depends on the arrangement of the urban geometry according to solar gains, and there is a correlation between energy savings and efficient urban design. The simulation results are validated with measured data from a case study in Stuttgart, Germany.

Optimization and Economics of Solar Cooling Systems

Abstract The two main market-available thermal cooling technologies with regeneration temperatures below 100°C are evaluated in this chapter. For closed cycle absorption chillers and open desiccant cooling systems, efficiencies, costs and optimization potentials are analysed. Measurements and simulation studies from realized demonstration projects are presented. If properly designed, both technologies offer significant primary energy savings. However, as coefficients of performance (COPs) are generally lower than for electrically driven compressor chillers, care has to be taken to reduce auxiliary energy demand. While measured average thermal COPs are between 0.6 and 0.7 for absorption chillers, desiccant units can reach higher values, as they often operate with evaporative cooling only. The electrical COPs can be as high as 11 for absorption systems with efficient cold distribution and recooling units and is about 7–8 for desiccant systems with an air-based distribution system. The total costs of both desiccant and absorption cooling systems are dominated by capital costs so that high full-load hours are crucial for an economic performance.

Potential of roof top PV-systems for supplying electricity in residential area Scharnhauser Park

This study is a part of a large scale urban development project called POLYCITY dealing with how to make cities more energy efficient. The project is already in progress in three different countries like Italy, Spain and Germany. We will keep our analysis focused only on German part Scharnhauser Park, which is located in Stuttgart. In this project the working and living places are integrated in order to get a sustainable city quarter with special emphasis on minimum travel distance and low energy consumption. As renewable energies are an additional source to conventional ones, they are more and more important for the production of the energy. The interesting feature is that a great deal of the necessary energy will be provided from roof top PV-systems and wood fired cogeneration plants. Laser Scanning data along with GeoMedia are used for finding the potentials of roof top. The analysis is also supported with Web Application to disseminate the information to the public. This approach will set a good example for supplying green energy in residential quarters and will provide a basis for the sustainability of similar communities.

Passive and Low Energy Cooling of Office Buildings

Abstract In this work, the cooling performance of night ventilation systems and different earth heat exchange technologies were experimentally analysed in three office buildings in Southern Germany. One of the first passive energy standard office buildings in Europe was extensively monitored over a three year period to analyse the summer performance of a highly insulated and well shaded building in which night cooling ventilation was based on stack effect and cross ventilation. This was combined with a mechanical ventilation system incorporating a ground coupled heat exchanger to supply daytime fresh air. For comparison, an energy analysis was made of a mechanically driven exhaust air night ventilation system and a supply and exhaust air system in the other two buildings. The first of these was a passively cooled refurbished building in Tübingen which utilises mechanical night ventilation to effectively discharge ceilings with phase change material. In addition, fresh air cooling is achieved using a horizontal brine-earth heat exchanger. The second comparison building was a low energy office building in Freiburg which uses water based ground coupled heat exchangers for fresh air cooling and an exhaust air ventilation system for night cooling. During a typical German summer, in which the number of hours that the ambient air temperature exceeds 25°C is less than 160, the passively ventilated building performed excellently, even with relatively high internal heat loads of 200 to 400 Wh.m−2.day−1. However, when the ambient air temperature was significantly higher, such as in the summer of 2003 (i.e. 3 K higher than the average summer temperature), nearly 10% of all office hours recorded room air temperatures above 26 °C. In the case of the two buildings that were night cooled by mechanical ventilation, cooling performance was limited by the rather low air exchange rate of 2 h−1. This resulted in overnight room temperature reductions of just 2–3 K during hot summer nights. Also the coefficient of performance (COP) was relatively low for this approach at between 4 to 6. All the earth heat exchangers showed excellent energy performances with COPs between 20 and 50. However, due to the limited fresh air volume flow in such buildings, the earth heat exchanger only removed a small part of the total load.

A Real-World Lab Approach to the Carbon Neutral Campus Transition: A Case Study

Universities, with their complex systems, influence on local economies and socio-cultural place-making, serve as a framework for the sustainable development (SD) transformation within communities. In support of Germany’s Energy Transition and the goal of climate neutral state governance by 2040, the state of Baden-Wurttemberg selected seven universities to create real-world lab projects addressing various sustainability-related themes. This paper presents a case study of the University of Applied Sciences (HFT) Stuttgart’s EnSign real-world lab, which employs transdisciplinary research methods to find transferable solutions for the transition to a climate neutral inner-city campus. EnSign’s approach includes the development of an iterative, optimization-based, knowledge capture process that is inclusive of both external and internal stakeholders. Goals are to catalyze the campus transition, adjust user behavior, and increase energy efficiency by developing new building operating concepts, public building renovation financing models, stakeholder integration methods, and institutional management structures. A brief review of the supporting policy framework, theoretical foundations, and topical areas of implementation are presented. Initial findings are described with regard to communication strategies, civil society integration, and institutional preparedness for the transition. Conclusions reflect on the relevance for real-world lab experiments.

Planning Tools to Simulate and Optimize Neighborhood Energy Systems

This section introduces different energy modeling tools available in Europe and the USA for community energy master planning process varying from strategic Urban Energy Planning to more detailed Local Energy Planning. Two modeling tools used for Energy Master Planning of primarily residential communities, the 3D city model with CityGML, and the Net Zero Planner tool developed for the US Department of Defense installations are described in more details.