ProKlim - Optimisation of Energy Efficiency of automated indoor climate systems by using weather forecasts
Using current weather information, such as outdoor temperature, to control heating and air conditioning in buildings has become standard procedure in building services engineering.
However, only few facilities within research or pilot projects use in addition weather forecasts for controlling the indoor climate, even though this can help existing systems to save energy and reduce CO2 emissions relatively easily and inexpensively.
Contents and Objectives
In collaboration with its project partner, the Austrian Institute of Technology (AIT), UBIMET analysed the basic energy savings potential for industrial buildings by including weather forecasts as a variable. The magnitude of the savings potential (in form of saved energy, costs and CO2 equivalent) was calculated. In this way, the savings potential could be separated regarding the factors forecast quality and savings owing to the building's geographical position. For the investigation, AIT carried out thermodynamic simulations for a test building in different regions of Austria (ENERGYbase). From the results, index numbers could be derived, quantifying the significance of the factors in terms of the energy saving potential.
Additionally, the topic of integrating the weather forecasts into the building automation was of interest. Consequently, in the second part of the study, a complete concept for integrating weather forecasts into the climate control systems of buildings was drafted. Within the scope of the feasibility study, the project partner ee-consult conducted a detailed analysis of the technological possibilities.
One of the most intricate parts of this project was the thermodynamic simulation of the investigated ENERGYbase building. For this reason, the AIT developed a very detailed model of the building including 68 thermal zones with approximately 750 ceiling and floor elements and altogether around 150 window panels. The thermal simulation was performed using the simulation software TRNSYS 17 and was validated with the actual monitoring data from the building. Already the first simulated scenarios demonstrated that the meteorological parameter influencing the indoor climate most is the direct solar radiation. In contrast, the outdoor air temperature has only a minor role due to the efficient insulation of passive houses.
Since weather stations only measure the total global radiation, UBIMET successfully developed a method for separating the measured global radiation into direct and diffuse radiation. Depending on the location the weather forecast achieved an accuracy of 38% to 98% when comparing the daily measured global radiation to the predicted.
By varying the prediction quality, the geographical location and the weather situation different scenarios were simulated. In this way, the influence of the various parameters describing the building, weather and internal loads on the tempature inside the building were determined.
The analysis of the building standard and the market potential of integrating the weather forecasts into the building automation was investigated by ee-consult with the help of public data and studies. Within Austria a large amount of data with respect to residential building could be identified. However, there was only an insufficient amount of data available for non-residential buildings within Austria. The only data being ascertained by 'Statistik Austria' within the last population census. For this reason, the ProKlim investigation is based on the results of the German energy agency which were used as well by the klim:aktiv programme in Austria.
For analysing the standard of infrastructure for building control there was no public data available. Therefore the market potential of integrating weather forecast in this case was investigated by establishing a direct dialogue with building control suppliers. On the basis of this and a publicly available Swiss study it was possible to obtain a profound approximation of the current market potential.
Over the whole observation span one recognizes a tendency that weather forecast based building control has a potential for cost reduction due to a more efficient use of the heating energy. Considering different regions and single days with different weather conditions, the amount of energy saving varies. In one single case the energy consumption had exceed the one for buildings without building control (about 2%). In summary, we find that there is a potential for saving heating energy of up to 40% assuming ideal predictions for the direct solar radiation and strong variations of the radiation during the day. Using more realistic predictions instead, heating energy savings of up to 20% are still possible. Averaged over a whole year we expect the potential amount for energy savings to be lower.
Additionally, we find that when using realistic instead of ideal weather predictions to estimate the energy saving potential it makes not, as originally expected, a difference whether one considers mountainous or plain regions. Although, in general, the energy consumption for heating depends on the geographic location, it is not possible to find a location dependence for the energy saving potential. However, our study shows that even for mountainous regions including weather predictions may save heating energy. Transforming the expected amount of energy savings due to predictive building automation into equivalent CO2-emission we find a value of up to 850 kg CO2 for ideal and up to 620 kg CO2 for realistic weather predictions where we considered the sum over all eight scenario days.
Based on the investigations of this project, we conclude that for buildings with a high insulation standard, as e.g. is the case for passive houses, the outdoor temperature plays a minor role in weather prediction based building control. In contrast to this, the direct radiation and thus the solar component has a strong impact on the building automation.
Consequently, the use of predictive building automation becomes important for intertial heating and/or cooling systems and in case of solar architecture. Hence, such systems are best to be applied in cases with a complex interplay between thermal inertia and controlled use of solar energy.
Prospects / Suggestions for future research Due to the projects character as basic research, the energy saving potential of predictive building control was only analysed marginally. Among others the results found have not considered the complex interplay between automation, heating system and solar architecture. The analysis is mainly based on the simulation of one building allowing us only a limited transfer of the findings to more general types of buildings in Austria. Additionally, it was not possible to integrate weather forecast operationally into existing building control systems yet. Nevertheless, the results underline the importance of further analysing the energy saving potential within a future project.
For a more thorough consideration it is required to find new methods as well as calculation tools. In particular the TRNSYS 17 software used for the thermodynamic building simulation will fail to analyse more complex situations. Only with an alternative approach and software, it will be possible to integrate weather forecast directly into automatic building control. In addition, future projects should, apart from heating and cooling systems, include a consideration of energy saving due to the buildings's own production of solar and wind energy.
Project managementDI Mario Kahn
Project or cooperation partner
- DI Christian Hettfleisch, Ing. Emanuel Gstach
AIT Energy Department
- Dr. Daniela Knorr