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Methodical error rectification and optimisation sequence.
© Plenum

Simplified scheme of the multiple boiler system in the LANUV Düsseldorf.
© Plenum

Comparison of old and new system operation: after optimisation the desired supply temperature is adhered to.
© Plenum
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Tools for energy-efficient building operation

Within the scope of the energy-optimised construction (EnOB) subsidy programme, a joint project between the ISE Fraunhofer Institute for Solar Energy Systems and partners from the scientific and industrial fields will continue until the end of 2013 to promote the detection of this optimisation potential in good time, and to access it in the long term. The model-based quality assurance (ModQS) project researches methods and tools for the building operation of the future. For this purpose, methods for commissioning and monitoring building services equipment systems are being developed based on as much measured operating data as possible. In order to be able to realise the method in practice, studies are also being conducted as to which measurement data is necessary for the different optimisation stages. The wide ranging approaches are currently being tested in seven larger office and school buildings.

The method sequence in Figure 2 for error rectification and subsequent operation monitoring shows the general approach. First, data such as flow rates, pressures, controller positions, pump rotational speeds and additional consumption information – possibly also with mobile measuring devices – is measured. Then, models are used to decide which information items are needed for the subsequent operational monitoring. For this data, controllers are being developed in order to be able to detect deviations from the target behaviour at an early stage. On the basis of a model and a dynamic simulation, the characteristics of the installed heating system are determined, and the controller parameters are calibrated in accordance with the measurement results (e.g. the pressure distribution in a hydraulic system). This is designed to enable continuous operation monitoring, in order to ensure energy-efficient operation in the long term.

Optimised multiple boiler control in the LANUV Düsseldorf

In the building housing the Landesamt für Natur, Umwelt and Verbraucherschutz in North Rhine-Westphalia, it became necessary to optimise the control of the multiple boiler system without hydraulic switches. Inadequate hydraulic compensation of the static radiators and defective thermostatic valves meant that high volume flows were required, while the temperature difference was low. The set supply temperature could at first not be maintained, and the heat consumers were undersupplied. This led to complaints by staff. It was also observed that the boilers started up very frequently, which led to a high degree of wear, a high thermal load and excessive consumption.

The building complex comprises a high-rise administrative building, two laboratory buildings and a workshop building with garages. Heat is supplied to the building via a multiple boiler system which is installed in the attic of the high-rise building, and which consists of two gas condensing boilers with outputs of 370 and 720 kW, and a low-temperature boiler with an output of 780 kW. The two condensing boilers are designed to provide the normal supply, while the low-temperature boiler only starts operation when large amounts of heat are required. All boilers are equipped with modulating burners. One single volume flow-controlled heating pump supplies four distributors. The heat is emitted via both radiators and ventilation systems. The boilers also provide hot water for the canteen and laboratories. The system was last modernised in 2006. The gas boilers were replaced, the distribution was simplified and the current building control system was installed. This reduced the generation output from 3 MW to 1.9 MW.

During the winter of 2011/2012, researchers began monitoring operations and found several major faults. The burner outputs failed to meet the anticipated values, the modulation areas were not used and the boiler temperature monitors were set too low. Taking comprehensive measurements as a guide, a central controller was developed on the basis of a model and the entire system operation was simulated. The input values for the simulation were the measured volume flows, outside temperatures and heat consumption levels. The controller was designed and simulated using Matlab/Simulink software. The new control is designed to maintain the specified supply temperature without changing the burner – although with as few burner starts as possible – and without hydraulic compensation of the consumers. This required a special controller concept. It was needed since in this system, subsequent standard boiler circuits failed to give a satisfactory result. In April 2011, the new central controller from Neuberger was put into operation. The parameters were adopted from the previous settings for the heating system and from the simulation results. The system operation functioned smoothly after the first adjustments had been made. Currently, the required supply temperature is maintained during system operation (Figure 4), while the number of burner starts has been reduced by a factor of 10.

Experience with the demonstration building at the LANUV in Düsseldorf shows that the method developed also functions when no hydraulic decoupling occurs between the generator and the consumer. The simulation allows potential errors to be detected and rectified in advance. During later operation, it also enables fast monitoring and error analysis, and can therefore be used for automatic monitoring of the system operation.

What is meant by operation optimisation?

Operation energy optimisation covers all areas which are of relevance to building operation, from an up-todate functional description through to effective energy management, and from the management of fault rectification through to user training. Alongside energy efficiency, studies are also conducted as to whether the atmosphere in the buildings is beneficial to the performance of the users. Existing buildings present far more complex challenges than new buildings. For example, in addition to the optimisation of the building operation itself, servicing, the replacement of individual components, retrofitting of building automation, the renewal of individual systems or the refurbishment or even dismantling of the entire building may be required. No investment should be made in a monitoring infrastructure until these obstacles have been removed.

From ModBen to ModQS

ModQS is based on the results of the ModBen research project at the Fraunhofer ISE. With the ModBen, a method and also a tool has been developed for analysing and optimising energy-related problems for building operation management. Typical problems which occur in practice are taken into account, such as a lack of data available and cost limitations. ModBen is able to identify potential savings and to monitor optimised operation with a low time delay on a largely automated basis. However, it became clear that in order to commission and optimise building services equipment systems, such as a hydraulic distribution system, further analyses are necessary. The goal with the ModQS is to extend the ModBen method to include measured value-based commissioning and operation monitoring, as well as the model-supported operation of heat generators. Here, the focus is on systems for the supply, transfer and distribution of heat in existing non-residential buildings.

Projektinfo 05/2013:
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Addresses

Project coordination, method development
Fraunhofer ISE

Data recording and measurement, realisation in demonstration buildings
PLENUM Ingenieurgesellschaft

Development of hardware and software
ennovatis Schweiz AG

Development of building commissioning methods
HAW Hamburg

Scientific consultation on modelling and control technology
Energieagentur Regio Freiburg GmbH

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