Sustainable ventilation systems in multi story residential buildings in the conflict areas of hygiene and costs

The goal of this project was to develop guidelines for hygienic and cost-efficient mechanical ventilation systems in residential buildings, in which maintenance and cleaning demands are described. These guide­lines are based on existing literature as well as practical experience of the property owners, finally they are based on results of hygienic measurements in existing ventilation systems conducted in this research project.

Short Description




Starting point / Motivation

In the last years the low energy and passive house standards for high volume residential buildings were intensively promoted both on national as well as on regional level. Correspondingly the number of ventilation systems with energy recovery increased. They are an integral part of energy efficient buildings, play an important role in the operation of these buildings and assure a good indoor air quality.

Inadequate constructional measures and undefined or inexplicit attendance processes or intensities lead in the past to more or less (un)satisfactory solutions resp. to unnecessary high costs for (structural) maintenance.

Due to lacking investigations the reasoning for the necessity for regular cleaning intervals of auriferous components of the ventilation system could not be answered sufficiently.

Both the project promoter as well as the property developer must ensure the operation of ventilation systems with energy recovery with­out complications. Both demand clear statements and guide lines to issues like long-term hygiene, operation costs etc.

Content and Objectives

The goal of this project was therefore, based on the hygienic and technical analysis of existing ventilation systems, existing literature, the practical experiences of the project partners, the expert panel, notable property developers and industrial partners, to develop clear guidelines and recommendations for a hygienic flawless and cost efficient ventilation system with energy recovery for high volume residential buildings.

These results should in particular support project promoters, property developers, industrial partners as well as the standardisation and legislation processes to describe maintenance and cleaning requirements and possibilities and to give answers to the related life cycle cost issue.


This project consists - beside project management - of four parts:

  1. the development of a detailed research design
  2. the examination of selected ventilation systems with energy recovery
  3. the analysis and interpre­tation of the measuring results
  4. the development of conclusions and guidelines including their dissemination

A panel of external experts and notable property developer were integrated in the development of the project design. This was the basis for the later detailed analysis of the ventilation systems. The key aspects were on investigating the real operational mode and the configuration, the hygiene of these systems (sample taking on the surfaces of air-ducting components and measurements of the indoor air quality) and cleanability.

The results of the investigations were documented in detail, appraised and analysed. Subsequently the conclusion and recommendation of this report were developed within the project team under inclusion of the above mentioned expert panel and the target groups.

Results and conclusions

The project results are available in the public research report. There recommendations for a code of best practise, for standardisation and legislature as well as supplementary working devices for identified key target groups (technical bulletin for property developers, check lists for ventilation engineers and craftsmen, information sheet for ventilation system cleaning) can be found.

18 representative ventilation systems with energy recovery in Austria were researched. The results show on the one hand the robustness of this ventilation concept, on the other hand optimization potentials, which should be utilized in any case.

From a hygienic perspective all investigated ventilation systems show a significant reduction of fine dust and fungal spores in the incoming air compared to outdoor air - thus an indoor air quality improvement due to the ventilation system compared to window ventilation. This reduces the allergenic resp. irritative potential compared to outdoor air, which is in particular worth mentioning from a human health perspective.

The intake air ducts were predominately in hygienically clean conditions. When the ventilation system was realized in a proper form with correct air filtration and when regular maintenance was done, there is usually no critical germal reproduction of bacteria or mold on the surface of intake air ducts. The degree of dust aggregation tended to increase over the time of operation and with low filter quality. The benchmark for a median cleanness quality class according to OeNORM EN 15780 trended to be exceeded by older ventilation systems and lower filter classes (range of approx. 10 years of operation). The limit value of dust aggregation in exhaust air ducts was many times exceeded in all examined and before 2006 constructed systems.

The cross section necking due to these depositions can lead to a considerably increased electricity demand of the ventilator. Therefore the cleaning of the system has an energy saving potential. Furthermore dust aggregations, beside thermal load, leads to a reduction of the volume flow rate in the contaminated section and can cause undesired constraint of the ventilation operation.

The basic requirement of replaceablity and cleanability of all plant components was not met by the researched systems. Frequent changes in profile, e.g. from rectangular to circular ducts, lacking revision vents and generally limited access to duct sections complicates cleaning operations. In addition currently only few companies have experience with the cleaning of ventilation ducts of apartment buildings.

The investigations showed practically at all 18 installations easily avoidable material, planning resp. construction shortcomings, which medium or long term will significantly affect maintenance costs of the ventilation systems. Life cycle cost analysis show that cleaning and maintenance are considerable cost portions.

Therefore it is also from this perspective indispensable to look in detail at the issue of cleanability of ventilation systems for a high quality, hygienically flawless and cost optimal performance already in the planning phase as well as during construction.


There is no way to bypass the requirement for ventilation systems with energy recovery taking hygienic and comfort reasons into account. The project results clearly show the necessity to intensify research on ventilation systems with energy recovery. This applies to the planning and construction of the systems as well as on maintenance issues. These are important preconditions for the aimed market penetration of energy efficient, life cycle optimized building concepts.

Project Partners

Project management

DI Beatrice Unterberger - bauXund Forschung und Beratung GmbH

Project or cooperation partners

  • e7 Energie Markt Analyse GmbH
  • IBO Innenraumanalytik OG
  • leit-wolf Luftkomfort e.U.

Contact Address

DI Beatrice Unterberger
bauXund Forschung und Beratung GmbH
Ungargasse 64-66 / Stiege 4 / 2.Stock
A - 1030 Wien
Tel.: +43 (1) 360 70 - 831
Fax: +43 (1) 360 70 – 808