smartEXT - extended application boundaries for proven passive house technology

The present study aims to explore the application options for compact units (ventilation devices including micro heat pumps, developed for passive houses) in low energy buildings. Compact ventilation units for heat recovery, heating and domestic hot water shall bear the basic heating load, whereas peak loads shall be covered by newly-developed auxiliary heating equipment combined with intelligent control algorithms. This allows increased energy efficiency as well as cost effectiveness together with higher living quality and lower ecological load.

Short Description




Starting point / motivation

The company drexel und weiss gmbh – passive house technology – is producer of sustainable environment-friendly compact units comprising heat recovery, heating and domestic hot water possibilities, suitable for buildings involving passive house standard (eg. heating energy demand < 10-15 kWh/m²/a) as overall systems.

Today’s buildings sometimes fail to match passive house requirements entirely however, due to cost monitoring reasons over lifetime typically. Then compact units currently cannot be applied (for these so called low energy consuming buildings) in an economic way.

Contents and Objectives

The present study aims to extend the application boundaries of compact units towards 20-25 kWh/m²/a, to bring the above mentioned technology of comfort ventilation into low energy consuming buildings and increase their dissemination therefore. To this end newly developed, locally placed auxiliary heating systems to cover peak loads are to be evaluated, while basic heating load is still beared by conventional compact units as a central ventilation system.

It has to be clarified whether under these conditions distribution losses can be minimised and energy efficiency as well as living quality will go up.

Methodological approach

To achieve the mentioned goals, auxiliary heating systems for three building blocks were selected, specified and dimensioned supported by simulation of heat flow, resulting temperature distribution and response times including parameter variation studies due to computational optimization. Furthermore development of control strategies resp. algorithms and single room control circuits, together with build-up of lab systems to combine auxiliary heating equipment and comfort ventilation.

Data sensing and recording equipment was implemented leading to comprehensive monitoring and verification of the expected results. User behaviour was recorded at the same time, making data comparison (with phpp studies) and evaluation possible in an easier way.


This investigation demonstrates (in its distinctiveness) hardly foreseen results and valuable findings. Among others, it shows – especially in this certain case of peak load covering – that in every case an overall system, including the user, has to be evaluated. Only then reasonable prediction is possible. It can therefore be assumed what we have to take into account when utilising the findings gained for low energy consuming buildings, resp. which kind of investigations are required further.

Passive house technology is suitable in low energy consuming buildings too, under certain conditions. We gain enhanced living quality and are able to achieve economical as well as ecological goals.


  • Simplified concept of ventilation, heat recovery, room heating and for domestic hot water
  • Reduction of financial expenses concerning building envelopes through extension of application boundaries of proven passive house technology towards 20-25 kWh/m²/a
  • Distinctly lower financial investment compared to customary (water driven) solutions
  • Equal or even lower energy consumption due to avoidance of storage and distribution loss as well as single room control circuits
  • Reduced maintenance and repair efforts because of less equipment parts.
  • Enhanced living quality due to the possibility of individual climates in every single room and utilizing radiation heat
  • Contribution to ecological as well as economic targets

Prospects / Suggestions for future research

Monitoring and feedback of preliminary findings show preconditions to successfully utilise this technology, as well as which items need further attention or investigation.

  • Suitable sensor technology to detect presence.
  • Deduced optimization of control strategy.
  • Compliance with rules developed during this study wherever possible (no loss of comfort, because of only usualness mostly)

Project Partners

Project management

drexel und weiss - Energieeffiziente Haustechniksysteme GmbH

Project partners

Contact Address

drexel und weiss
energieeffiziente haustechniksysteme gmbh
Ing. C. Drexel, GF
Achstraße 42, A-6922 Wolfurt
Tel.: +43 (557) 447 895 0
Fax: +43 (557) 447 895 4