CiQuSo - City Quarters with optimised solar hybrid heating and cooling systems
Cities, as the main users of energy and polluters of greenhouse gas emissions, need to play a decisive role in shaping and implementing the necessary energy transformation in order to achieve the ambitious political targets and Austria's formulated climate and energy goals. Consequently, neighborhood planning with the objectives of implementing urban energy efficiency, the urban use of renewable energy sources and the use of ecological building materials is an effective lever and is currently subject to an intense discourse in science, politics and practice. Cities are currently far from exploiting their sustainability potential (reduction of greenhouse gas emissions, reduction of final energy consumption and increase in the share of renewable energy sources). Cities are those places where the great transformations are triggered and lived, where innovation comes to bear, and which have a substantial density of actors to implement the necessary actions and measures.
In this context, the comprehensive use of solar energy plays an essential role in urban planning. The Energy Research and Innovation Strategy for Austria 2017 clearly describes the vision for buildings and neighborhoods: "Plus-energy neighborhoods are the building standard and at the same time an integral part of attractive and livable urban areas and cities. Getting closer to this vision requires research and implementation projects that provide a solid basis for technical system solutions that make greater use of the urban solar energy potential. This final report of the project CiQuSo is intended as a contribution to providing the first foundations for possible technology system solutions with solar heating and cooling at the urban district level in the early development phase of neighborhood planning.
Contents and Objectives
The main objective of this completed "Stadt der Zukunft" project of the first call for proposals was the development, evaluation and optimization of system solutions for solar heating and cooling at city district level. To this end, the focus was on developing a method that quickly identifies optimal urban solar system solutions at neighborhood level. Thanks to this method developed, the potential for optimized solar energy use for urban heating and electricity supply is to be quantified in the early development phase of neighborhood and district projects, with special consideration being given to innovative solar hybrid heating and cooling systems and energy exchange across buildings.
Finally, the neighborhood optimizations of many possible technology combinations of suitable solar hybrid heating and cooling systems for a defined building neighborhood (quarter) should identify the one that leads to the best results with regard to a selected target parameter, taking into account the energy exchange across buildings (electricity and heat). The feasibility of the developed method for solar neighborhood optimization is to be demonstrated by an investigation of an exemplary building neighborhood from the Salzburg district of Itzling.
In general, a quarter is characterised by the diversity of its different building types, its energy supply systems and its energy management through complexity. The modelling approach determines the necessary simulation time and the achievable result quality for neighbourhood optimisation with computer-aided methods. According to the state of the art, the co-simulation of suitable expert tools is a possible solution for computer-aided neighbourhood optimisation. This methodological approach entails a high modelling effort and long computational time for the identification of optimal technology combinations is to be expected.
In contrast, the developed CiQuSo method of solar neighbourhood optimisation is based on three main blocks:
- Simplified RC building models: These are simplified substitutional models and reflect the thermal building behavior of selected building types.
- BlackBox models: These are substitutional models and reflect the energetic system behavior of the defined solar hybrid heating and cooling systems.
- Network algorithm: Assigns an HVAC system to each building in a city quarter and executes an optimization algorithm.
- In particular, new territory was entered for the creation of substitutional models for the simplified mapping of the dynamic operating behaviour of solar heating and cooling systems and artificial neural networks and decision trees were used, analyzed and improved for BlackBox modelling. Furthermore, a quarter algorithm was developed, which assigns a solar heating and cooling system to each of the buildings in the district and executes an optimization algorithm. Quarter optimization can simultaneously calculate the following optimization goals independently of one another:
- Optimization of heat self-consumption, i.e. obtaining as little thermal demand as possible from the grid for the quarter
- Optimization of electric self-consumption, i.e. obtaining as little electricity as possible from the grid for the neighborhood
- Primary energy optimization, i.e. where is the lowest primary energy required
- CO2 optimization, i.e. where is the CO2 emission lowest
- Economic optimization, i.e. which configuration can be used to achieve the above goals with minimum costs (annuities)?
In summary, the following results were achieved:
- Investigated, evaluated and optimized energy-efficient system solutions for solar energy supply at building and city district level: These were modelled in a corresponding simulation environment and the energetic operating behavior was simulated and evaluated. For each calculated solar system solution, the thermal or electrical load shift potential is quantified, and the system was evaluated ecologically, energetically and economically.
- Generated and modelled novel, solar hybrid energy systems based on photovoltaics and solar thermal energy for city districts.
- Developed method for neighborhood optimization considering energy exchange between buildings (heat and electricity). To create simplified substitutional models and to execute them for the neighborhood option, the reference data had to be omitted due to insufficient imaging quality. The CiQuSo method was adapted and the network algorithm uses the basic models and their result time series of the simulation environments EnergyPlus (buildings) and TRNSYS (SHC systems) for optimization.
- Feasibility study for the solar heat supply of the Salzburg Goethesiedlung by a large solar collector system. The results include a dimensioning proposal and the integration of a seasonal storage tank with thermal heat pump on the one hand and the energetic evaluation on the other.
- Demonstrated applicability of the developed CiQuSo method by selected building neighborhoods within the Salzburg city district of Itzling. To demonstrate the functionality and performance of the alternatively implemented CiQuSo optimization method, six buildings were selected as representatives from the Itzlinger Quarter. From several tens of thousands of possible combinations, the city quarter optimizer has identified those technology solutions that lead to the lowest CO2 emissions, the lowest primary energy demand (non-renewable share) and the lowest electricity and heat imports into the neighborhood. Comparison scenarios were defined and compared with the optimization case using the best data sets at building level. The modelled solar-hybrid heating and cooling systems deliver promising results for district solutions.
- A working web-based CiQuSo visualization tool (prototype) for the interactive demonstration of the developed method for neighborhood optimization and illustration of the pre-calculated results was developed.
Outlook & Recommendation for future research
In general, the functionality of the developed CiQuSo framework could be proven. For future research and development work, the further development of the CiQuSo-Framework 2.0 through the development of simplified mathematical-physical models for mapping the thermal building behavior and the energetic operating behavior of the building technology systems appears to be purposeful. The general challenge is to find an acceptable compromise between acceptable calculation time and sufficient calculation quality of the simplified models.
Due to the national funding priorities in the "Stadt der Zukunft" programme towards plus-energy neighborhoods, it is to be expected that neighborhood projects with solar-hybrid technology solutions and the associated infrastructures for cross-building energy exchange are in preparation and demonstration projects will be launched. The question of energetic neighborhood optimization will come up and methodical approaches and selected basic results of the CiQuSo project will form an initial knowledge basis.
AIT Austrian Institute of Technology GmbH, Energy Department