Passive House

Content of the presentation

This paper presents a thermal simulation validation study of the typical precision that a trained thermal simulation engineer can expect to obtain for the simulation of a room connected to a naturally ventilated double skin facade. The open source building thermal simulation tool EnergyPlus is used to predict air and surface temperatures in a free running weather exposed test cell.

The increasing number of highly insulated and air tight buildings leads to the concern of indoor environment overheating and related comfort and health issues. This can already happen in a temperate climate as found in the Netherlands. This work studies the ventilative cooling process as a possibility to avoid overheated dwellings. A monitored dutch passive house was modelled in Trnsys and the impact of increasing air flow rates on indoor temperatures was simulated. The most overheated zone was chosen to be analysed.

Highly energy efficient buildings such as ones built to the Passive House standard, require a very airtight building envelope and the installation of a mechanical ventilation with heat recovery (MVHR). MVHR systems incorporate ambient air filters, which reduce the introduction of particulate matter (PM) from outdoor sources into the dwelling. However, indoor PM sources, e.g. cooking, can also contribute substantially to occupants’ exposure and need to be accounted for when designing ventilation or deriving recommendations for filter classes. 

An airtight building envelope ensures not only the energy-efficiency of a building, but also a damage free construction. Important to achieve optimal airtightness are the planning, implementation and materials. Long-term airtightness requires efforts in all three aspects. Airtightness products are being tested under lab conditions but these results cannot be transferred one-on-one onto buildings.

In response to the European Energy Performance Buildings Directive 2010/31/EU and the Energy Efficiency Directive 2012/27/EU, buildings have increasingly become more insulated in order to reduce the heating losses to a minimum. However, this could also lead to the problem of indoor high temperatures during warm and transition seasons. Furthermore, the Intergovernmental Panel on Climate Change (IPCC) warns about increases in temperature of more than 4 ºC by the end of the century.

The paper investigates the possibility for using a traditional ventilation system with ceiling mounted diffusers to provide heating under winter time conditions in relatively cold climates – in buildings with low transmition losses such as “passive houses”. The analysis is done through a number of CFD simulations of a simplified office. It is shown that even small over-temperatures reduce the Air Change Efficiency substantially. On the other hand even very small internal heat sources increase the efficiency.

The future is well-isolated buildings with low heating demand. The first office building in Norway satisfying the passive house standard, the GK environmental house in Oslo, was taken into use in August 2012.

The impact of over-tempered air on the perceived indoor climate was evaluated by questionnaires filled in by the users of the first office building with passive house standard in Norway. In this building, the heating demand is covered entirely by warm air supplied into the rooms through the ventilation system.

The Marienlyst School is the first educational building in Norway built according to the passive house standard. This building benefits from a super-insulated and airtight envelope. While this reduces the heating demand largely, it also enhances the risk for poor indoor air quality and overheating compared to conventional buildings. It is therefore particularly important to implement an efficient ventilation strategy in order to avoid adverse effects on the health, well-being and productivity of the pupils.