Design of passive houses ENERBUILD

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This debate is an outputof the ENERBUILD project. In discussions about Passive Houses, often an image of a high-tech house, with no heating and very little freedom to design, comes into mind. Since a Passive House is meant to achieve certain goals by following certain rules, this seems to also become the main direction for the design, its architecture and aesthetics.

Passive-house1.jpg

Boring or dull architectural design

Objective

The goal of the report‘s following part is to encounter presumed problems regarding the ‚Boring architectural design‘ of Passive Houses. The presumed problems are described and then compared to current facts and studies. Propositions for solutions, killer arguments, and/ or opportunities are provided for each part of the discussion.

The next chapters cover the compact design of Passive Houses, including their flat roofs and thick walls. Also, the Passive House approach to window openings is given below, as are technical installations that have an impact on the external appearance of the building. The last section will provide information about the variety of Passive Houses and their blending in with the context.

Presumed problems

Constructing an energy efficient Passive House means to be limited to certain principles to achieve the demanded performance, particularly a good surface-to-volume ratio that is manifested in a compact building. These rules restrict the architectural design and variety of newly built Passive Houses.

Passive Houses consist of flat roofs, thick walls, and thus deep reveals (cf. killer argument ‚Bad Illumination‘). Light enters the building via large window openings on the south façade, but no or only small window openings are facing north. Often, photovoltaic elements and/ or solar collectors are found on the roof or the façade, and ventilation channels or shafts are visible, thus a Passive House can be easily identified. With the mentioned parameters, Passive Houses do look very alike, and often they don’t fit their urban context (e.g. conventional homes).

Analyses

Compact design, flat roof, and thick walls

Detailed article: Compact design, flat roof, and thick walls

These three architectonic characteristics all help to minimize heat loss.

  • Compact design: it minimizes the surface area through which heat could transmit and get lost.
  • Flat roof: it ist often part of the compact design approach and also imparts the modern spirit. It reduces the roof area, through which heat could be lost.
  • Thick walls are constructed in order to insulate the house. The wall thickness is the outcome of the constructional part and an additional insulation thickness of 25-40cm. Thus, the total width of a Passive House wall becomes easily about 40-55cm.

Window openings

Windows are the most crucial part of a passive house building. Orientation, size and glazing of windows are highly important.

In general, windows provide the interior with natural daylight, the determine views and connect the outside with the inside, thus extending the percept space beyond the boundaries of the building itself. In a Passive House, even as windows are highly insulated, they are still the most crucial part of the building’s envelope as they achieve significantly higher (= poorer) U-values than opaque surfaces. Hence, there is generally more energy lost passing through the windows than through walls.

If the design foresees large window openings, the energy loss also becomes larger. In the case of orienting large glazing areas towards the equator, however, the heat loss is compensated by greater heat influx (which is accordingly higher on large than on small windows). Orienting windows to the south takes advantage of the free and passive solar energy that also contributes to the heating. Facing windows east or west, however, can more easily lead to overheating in summer while providing less solar gains during the heating period. „Windows need careful planning and, where necessary, appropriate sun protection. The window specifications needed to achieve the Passive House standard depend on the local climate conditions” (iPHA, 2010a, p.9). Since there are many different types of glazing units available, the right one for each occurring situation can be chosen, e.g. double glazing on the south façade for more solar influx, and high performing triple glazing on the other sides of the building to minimize thermal energy loss (for further aspects of windows, their elements, and installation, refer to killer argument ‚Bad illumination‘). Built examples as the Passive-Energy-Standard Housing in Salzburg, Austria show, that the Passive House standard can also be achieved by treating the windows equally on both sides of the building - the southern side and the northern side. (cf. Detail 6/2007, p.652ff)

For more information, see also:

  • Daylighting

Technical installations (e.g. ventilation channels/ shafts, thermal solar collectors, or photovoltaic panels)

A passive house makes no use of a conventional heating system (e.g. burning fuel to produce heat), but receives its heating by passive solar influx and the heat recovery unit of its mechanical ventilation. Basically, one technical system is traded for another more efficient one. Therefore, chimneys and fuel storage tanks (and the space which is needed to install them) are not needed any more. Sometimes ventilation channels or shafts can be noticed. They provide the mesystem with geothermic preheated incoming air.

Additionally - often to provide warm water – thermal solar collectors can be installed at the roof or the façade. As the direct solar influx for space heating, they also make use of the free solar energy to heat water that is used in the building.

Since almost every building is in need of electricity, some builders or investors install photovoltaic elements, to cover some or even all of the electric power they consume. Often the investment is taken to qualify for subsidies or in case the building is located remotely and not connected to the power grid. One example for the latter is a refuge on the mountain Hochschwab, Austria, at 2.154m. Due to its high alpine surroundings it has to be self-sufficient and also take ecological care in regard to its sewage. According to the Passive House concept, e.g. it is optimised to efficiently use solar energy. (cf. Treberspurg/ Hofbauer, 2006, p.22ff) (cf. Detail 6/2007, p.624-627).

In an optimal planning process, the requirements of a Passive House can be met with conventional elements (cf. Menti, 2009, p.26-32).

Variety and context

The concept and standard of a Passive House is restricted to specific energy efficiency. These limits place all Passive House buildings in the same process, to meet the required standards. Even if the goal is the same, the ways to get there are manifold. Passive House technology is not restricted to specified shapes or materials. Every architectural style and every idea of dwelling can be put into practice, no matter if it is a mansion, a residential home, a high-pitched roof, or a cube. The question of ‚how to live?‘ is not limited either. Modern open floor plans with flowing transitions of spaces are as possible as a rather closed floor plan with strictly divided rooms. Construction material can be used as diversely (cf. Graf, 2003, p.7). While, often, residential Passive Houses are being built in the Passive House standard, other types of use and public buildings are also possible and even refurbishment projects can meet the Passive House standards (e.g. the former Post Office building in Bolzano, Italy).

As designing a Passive House building leaves freedom to layout, size, placing the windows etc., it is possible to blend into the urban context while achieving the energy values with rather subtle measures. It is also possible, and that is maybe where the boring image of a Passive House came from, to focus solely on the energy efficiency of the structure, the orientation etc., and thus the architectural design was rather neglected.

Not to forget, there might also exist building codes and restrictions which dictate very specifically, where, and how to place a building on the site. Again, these still leave many possibilities to planners, investors, and architects for how to react and design.

As mentioned earlier, sometimes, remote locations even predetermine the use of an autarkic concept as the Passive House.

Killer arguments (A) and opportunities (O)

Compact design, flat roof, and thick walls

K: A compact design minimizes the surface area through which energy could transmit. Thus, it reduces the volume within the complete thermal envelope. Less volume has to be heated while the maximum usable net area is provided. Through simpler construction, fewer costs are spent. A less compact design can be compensated for by other means (e.g. better insulation, more efficient use of passive solar energy, building service engineering, etc.) (cf. Menti, 2009, p.26-32).

K: The flat roof is part of the compact design approach. It also minimizes the roof area while providing a fully usable space underneath. It imparts the modern spirit, i.e. innovation.

K: The wall thickness is due to energy efficiency which can be achieved by the application of 25-40cm of insulation. An alternative are vacuum insulation panels (VIP), which provide the same K: A compact design minimizes the surface area through which energy could transmit. Thus, it reduces the volume within the complete thermal envelope. Less volume has to be heated while the maximum usable net area is provided. Through simpler construction, fewer costs are spent. A less compact design can be compensated for by other means (e.g. better insulation, more efficient use of passive solar energy, building service

engineering, etc.) (cf. Menti, 2009, p.26-32).

K: The flat roof is part of the compact design approach. It also minimizes the roof area while providing a fully usable space underneath. It imparts the modern spirit, i.e. innovation.

K: The wall thickness is due to energy efficiency which can be achieved by the application of 25-40cm of insulation. An alternative are vacuum insulation panels (VIP), which provide the same.

Window openings

K: Window openings of a Passive House provide daylight and view. They are not needed for ventilation any more, but they have to complete the thermal envelope of the building. Triple, quadruple or vacuum glazing can achieve low Uw-values. Large windows should be facing south, since the solar influx in one year more than compensates for the heat loss via the glass. Also, overheat protection must be considered through particular balancing solutions (e.g. ventilation, sun protection, heat storage medium) (cf. Menti, 2009, p.26-32). New products are being developed, that reduce the dimensions of the window frame. Overlapping the frame with insulation provides less thermal loss while showing less of the frame from the outside.

Technical installations (e.g. ventilation channels/ shafts, thermal solar collectors, or photovoltaic panels)

K: In many cases, a Passive House is heated by passive solar influx and an MVHR unit. A ventilation channel/ shaft through the ground would pre-heat the incoming air (or pre-cool it in summer). This system guarantees hygienic air renewal, while minimising energy losses via ventilation. However, air heating is not mandatory. (cf. Menti, 2009, p.26-32)

K: Thermal solar collectors are an option to passively use the sun to heat water for different uses (or another liquid as transfer medium). Their use has advantages since renewable energies are put into calculation with lower impact; thus, they improve the overall performance (cf. Menti, 2009, p.26-32). BIPV (building Integrated PhotoVoltaics) components can reduce the impact on architectural language [1]

K: Photovoltaic elements can provide electric power to the building or put the produced power into the public grid (e.g. for receiving subsidies or as the energy strategy of an Energy Saving And Producing (ESAP) building). BIST (building Integrated Solar thermal collector) components can reduce the impact on architectural language [2]

Variety and context

O: As many publications show, the variety of Passive Houses designs is great. Passive House components do not have to look like they were applied isolated from the overall design of the building they are given to. Early on in the planning process, many architects and planners commit to the Passive House standard. Thus, with an early integrated approach, the advantages of Passive House components and philosophy can be combined with ambitious architectural design. As different as are situation and planners, so are Passive Houses (e.g. refer to www.passivehousedatabase.eu, www.passivhausprojekte.de, current publications).

O: As some sites are quite remote, the autarkic system of a Passive House is an excellent option to construct a self-sufficient building ‘off the grid’ within such a context. (cf. Sulzer, 2009, p.46-50)

Further opportunities

O: All parties involved (builder, planners, architects) need to commit to the Passive House standard from the very beginning of the design, since upgrading a low-energy house to a Passive House often leads to disproportional higher expenses. (cf. Menti, 2009, p.26-32)

O: If architects and engineers are new to the energy efficient building sector, they might need assisting professional expertise. They need to consciously integrate energy (= cost) matters from the very start of the designing and developing process. For example, the quality and form of the envelope (air-tight, well-insulated, triple glazed windows, reduced/ no thermal bridges) is a crucial element concerning energy saving and conservation. (cf. Ragonesi et al., 2009, p.6,8). To catch up on new developments and implementation strategies, advanced training for architects and planners is available (in Switzerland, e.g. for the Minergie-P standard. As planners improve their knowledge, also owners or users of Passive House buildings need to be informed on how to run a Passive House in an energy efficient manner. (cf. Menti, 2009, p.26-32)

Contact and editor

Editor: Lucerne University of Applied Sciences and Arts – Engineering & Architecture on behalf of ZVDK

Lucerne University of Applied Sciences and Arts

Technikumstrasse 21

CH-6048 Horw

http://www.unilu.ch

Further information

ENERBUILD publication Killer arguments and opportunities for energy-efficient construction and the passive house

References

Killer arguments and opportunities on energy-efficient construction and the passive house (2011)