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Passive Houses for dummies

For many years now, since 2003, the second weekend of November hosts the International Passive House Days: Passive House owners and residents around the globe open their Passive House homes and offices and share their experiences, showing what this “Passive House” idea/concept is all about.

Hungary joined this initiative in 2009, when the Hungarian Passive House Association (MAPASZ) became responsible for a local program. In 2012 the Association of Hungarian Passive House Architects (PAOSZ) followed this lead and offered its own, separate set of programmes which resulted in an even more adequate coverage of these innovative and energy efficient buildings here in Hungary.

To complete the picture, an EU-funded project dedicated to the topic of nearly zero energy buildings (Nearly Zero Energy Buildings Open Doors Days) also organised building visits this year which partly overlapped with the other two tours (organised by MAPASZ and PAOSZ), but ensured the mobilisation of further interested parties to engage with this global event.

This year Geonardo – within the frame of its AIDA project – joined forces with MAPASZ in order to reach out to and mobilise an ever increasing number of people who are genuinely interested in the concept of Passive Houses and the related advanced building engineering technologies. Similarly to previous years’ experience, only a small fraction of the participants had an architect or similar building industry-related background: the majority of them were only open to the concept and wanted to learn more about the featuring success stories, or wanted to gather some operational experience before they engage into their own passive building project.

The first day covered a wide array of innovative buildings from Western Hungary featuring a few private homes, a school, a dental clinic and an apartment building, demonstrating that not only regular houses can be considered when developing such a project but essentially any type of building can achieve this cutting-edge energy standard. Despite their versatility, the buildings on display had a few basic features in common which are absolutely essential when it comes to a nearly zero energy building (nZEB) or passive house. The most important of them are air-tightness and thermal insulation.

It is easy to understand that if you want to have an energy efficient real-estate you can’t afford wasting energy on heating or cooling the outside environment as a result of a “leaking” building envelope. This is especially true if you have a renewable-based low-temperature heating system planned/installed with an output just sufficient (with little reserve) if the building meets certain energy standards but which might prove inadequate if the structure fails to comply with those initially planned figures. The blower-door test is a common tool to measure the air-tightness of buildings: “Blower door tests are used to assess the construction quality of the building envelope, locate air leakage pathways, assess how much ventilation is supplied by the air leakage, assess the energy losses resulting from that air leakage and to determine if the building needs mechanical ventilation.” (source: Wikipedia).

The test is highly recommended when there is still some room to fix the potential problems at a relatively low cost (half-ready status), rather than wait until the building is finished, only to engage into costly repair works aiming to bring the house up to the planned standards.

One of the main highlights of the first day came when the owners described their reactions when the blower door test concluded its findings on the given building.

Some of them were relieved that the construction crew did its job properly securing the air-tightness of the property while others were quite disappointed by the results. Since the Passive House technologies and standards are relatively new there aren’t many contractors prepared enough to tackle the challenges such a job requires.

We were told that most of the tasks which make the difference between good and poor results (an additional layer of sealing around the windows, a bit more filling around the cables entering the structure etc) require no special knowledge or ability to perform them, rather patience, a bit of time and devotion. The latter of which is usually lacked by the crews responsible for the job. The general consensus was that you have to do these tedious bits for yourself if you want them properly done or you might face costly consequences to get them fixed.

It’s a cliché that thermal insulation is a key factor when it comes to energy efficiency of buildings, and in case of nearly zero energy buildings or passive houses it gets even more important.

There is a relatively wide range of building materials that are suitable for such buildings, but their inherent thermal properties alone wouldn’t make them fit for the purpose without additional layers of thermal insulation applied over them either from the inside or the outside. On our tour we came across various structures built of regular, hollow, fired clay-bricks, sandlime bricks or even cast-concrete, demonstrating that personal preferences can be taken into consideration when building an energy efficient structure and that there is more than one way to skin the cat.

For instance, the owner of the concrete building said that his home was erected in just under 2 months. Insulated concrete form (ICF) is a system of formwork for reinforced concrete usually made with a rigid thermal insulation that stays in place as a permanent interior and exterior substrate for walls, floors, and roofs. The forms are interlocking modular units that are dry-stacked (without mortar) and filled with concrete. The units lock together somewhat like Lego bricks and create a form for the structural walls or floors of a building. Because of the uniform wall structure there is no surprise that this house’s blower door test results were by far the best among the ones visited. But in my personal opinion I wouldn’t want to voluntarily live in a reinforced-concrete-walled house even though its energy performance, speed of delivery and visual appearance makes it a quite appealing option. The rest of the programme buildings followed a more traditional wall structure using different types of bricks with various thickness of insulation covering them.

In general it can be said that the main difference between a passive house and a regular home lies in the thickness of the insulating layer and in the quality of finishing.

When it comes to passive houses or highly energy efficient buildings a common concern is usually raised about not-to-be-opened windows. It makes sense to rely on the mechanical ventilation, and not to use the windows for uncontrolled ventilation once you spent so much on making your structure air-tight and thermally insulated. All of the buildings in our programme were equipped with such a system; thanks to their sophisticated ability to heat the fresh air from the outside using the heat of the used air from the inside, they minimised the amount of energy needed to maintain comfortable indoor temperatures and moisture levels. Hence we were told that in case guests are over, they might end up overheating the house simply through the overall body heat, so the fans need to be turned higher to cope with the increased demand.

 

It is quite fascinating to see that adequate air tightness and thermal insulation may render regular heating options obsolete or even futile. Some of the visited buildings had been equipped either by radiators or floor heating, but only as a backup, since 99% of the time ducted-air heating meets the needs.

Of course passive house owners may also use their windows in a traditional way (unless they choose fixed windows), but they usually do so when the temperature difference is minimal between the inside and the outside (Spring, Autumn etc). In all other cases they have uninterrupted access to fresh pre-heated or pre-cooled and moisture-controlled air via their heat-recovering ventilation system and they do not have to waste the energy they used to heat or cool the air inside when opening the window for fresh air. Nowadays many manufacturers offer amazingly compact devices which could even fit in your kitchen cupboard and take care of all building engineering tasks (heating, cooling, ventilation, DHW) in a single unit, though such a sophisticated piece of engineering comes with a hefty price tag.

Some owners prefer these types of solutions, though the more complex the design, the more specialised maintenance has to be done in case something goes wrong. We have seen a few buildings where the owners were pursuing to keep the building engineering system as basic and easy-to-repair as possible. A young couple for instance after having an air-tight and thermally insulated structure with a simple heat recovering ventilation in place, added only electric heating films to cover for their additional heating needs, if necessary using their solar PV produced energy. It is a plain, simple, cheap and easy-to-maintain solution.

Though the number of newly built and retrofitted passive houses and nearly zero energy buildings are getting more and more numerous, year by year the total number of such buildings is still in the range of a few hundred at tops, compared to the 4.2 million homes in Hungary. On one hand it is delightful to see this tendency in Hungary, but on the other hand these innovative structures can only be considered as the few exceptions to the general rule so far. A rule which still represents the traditional way of building a home using outdated approaches, concepts and materials. As long as this is the prevailing rule, such buildings will remain a minority and no bigger scale building energy targets can be met effectively.

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