Forschungsprojekt - SLIM Semizentrale Lüftung und intelligentes Betriebsmonitoring; Teilbericht 5: Ventilatortausch bei Bestandsanlagen - Betriebspunktanalyse und Wirtschaftlichkeit

Abstract

This sub-report 5 sets out to develop an automated operating point analysis for fans in ventilation and air-conditioning systems (HVAC systems). The aim is to accurately determine the actual operating conditions in order to systematically assess and improve the energy efficiency of existing systems. The basis for this is the specially developed fan tool (Operating Point Analysis Tool, BaT), which models fan characteristic curves based on a small amount of input data - such as measured or manufacturer-provided values - and thereby enables the precise determination of air flow rate, pressure and power consumption. The tool uses cubic spline interpolation with four characteristic control points on the pressureairflow characteristic curve. Operating points for different rotational speeds are calculated using the proportionality laws between rotation speed, pressure and airflow. The influence of the motor, V-belt and frequency converter is modelled via partial efficiency values and partial load factors. To this end, three established models (ILK Dresden, VDI 6014, EBM-Papst) are integrated into the tool to simulate a realistic overall behaviour of the drive system. A key innovation is the ability to generate characteristic maps from measurement data where only electrical power, pressure difference and flow rate are measured. Aerodynamic efficiencies and operating points are derived from this data through iterative calculations. Alternatively, existing manufacturer characteristic maps can also be entered directly into the tool. If a fan characteristic map is known, the operating point of a system can thus be determined solely on the basis of pressure and rotational speed measurements during actual operation. For validation, the method was tested on five HVAC systems at the University of Kassel, which featured different fan types and control strategies. The measurement results show that the developed method can reliably map both performance curves and actual operating behaviour. The tool enables the analysis of existing systems, the identification of inefficient operating points and the quantification of energy-saving potential. Further development is required, particularly in refining the motor partial-load models and taking real installation conditions into account. Overall, the study demonstrates that automated operating point analysis is an effective tool for assessing energy efficiency and for data-driven operational optimisation in existing buildings. In addition, the technical feasibility as well as the energy and economic potential of replacing fans was investigated. To this end, the energy-saving potential of replacing existing fans with modern EC fans was assessed for five central units. The replacement was carried out on a suitable unit as an example. The subsequent test measurements with the new EC fans show that the theoretically calculated savings are achievable in practice and illustrate the conditions under which economic benefits can be achieved through fan replacement. A further focus was on the implementation of semi-centralised ventilation in the DIN standard 18599 "Energy efficiency of buildings". In the revised version of 2025, an additional value for the constant-pressure fraction of fp = 0 for semi-centralised ventilation has been included in Table 8 of DIN/TS 18599 - Part 7. This makes it possible to reflect the energy savings achievable through semi-centralised ventilation within the scope of the standard calculation. Furthermore, the report outlines approaches for the further development of the standard’s content, with a view to enabling ventilation systems to be assessed more systematically and accurately in future. A supplementary area of focus concerns the evaluation of contracting models for the implementation of energy-efficient ventilation systems. In particular, energy-saving contracting and air supply contracting are identified as suitable financing and operating models. For HVAC systems with high renovation potential, these models enable the implementation of efficiency measures without investment by the owner. This reduces the risks for the operator and ensures continuous operational optimisation throughout the entire contract period. The economic analyses show that the combination of efficient fan technology and monitoring systems enables shorter payback periods and long-term energy and cost savings. Contracting is therefore generally recommended as a tool for the cost-effective and sustainable implementation of the developed technical solutions in the existing building stock.