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When old buildings are renovated, it is often difficult to achieve Passive House standard. Typical reasons for this are unavoidable thermal bridges as well as a general building design, which was originally not optimized for compactness and solar gains. For such buildings, Passive House Institute (PHI) has introduced the EnerPHit standard. The basic principle is to modernize all relevant parts of the building with Passive House components. This way almost all advantages of the Passive House standard can be realized in retrofits, even if the heating demand is not reduced all the way down to 15 kWh/(m²a).
In the past the requirements for Passive House components such as windows and ventilations systems were only defined for cool temperate climates as prevails in Germany and Central Europe. As the EnerPHit criteria are based on the requirements for Certified Passive House Components, the first version of the EnerPHit criteria published in 2010 was also applicable to buildings located in cool temperate climates only. However, this also already included locations outside of Central Europe with similar climatic conditions, such as New York. Additionally EnerPHit renovations in other climate zones have been certified as pilot projects, such as a family home in the colder climate of Minneapolis, USA.
In the recent past PHI has carried out intensive research with the aim of defining truly international component requirements. An international certification scheme for Passive House windows is running with 6 windows for colder climate zones already certified. International requirements for other components have been defined, with corresponding certification schemes to be set up in the near future.
The development of international Passive House component requirements has now progressed far enough to serve as a reliable basis for international EnerPHit criteria. In November 2013 a project team at the PHI (led by the author) has completed a beta version of the international EnerPHit criteria. This article describes the requirements as well as how they have been derived. It is important to keep in mind that these are preliminary requirements that may still be subject to change until the official release of the certification scheme.
General derivation of the international EnerPHit component requirements
The requirements for individual building components continue to be the core of the international EnerPHit criteria. Switching to a reference building procedure has been considered during the development process. However, this idea has been dropped again, amongst others due to the resulting double effort of calculating the reference building as well as the real building with the PHPP.
As stated above, the international EnerPHit component requirements are based on the requirements for Passive House components. These requirements have been derived by means of an economic optimization process. The process has been carried out for each location in a grid of climatic data sets covering the whole globe, with the aim of finding the set of component qualities with the lowest life cycle costs for an example building. 200 combinations of different ventilation, window and shading qualities were additionally combined with different insulation levels of the opaque building envelope (for a more detailed description of the method see [Feist 2011]). The combination with the lowest sum of investment and energy costs could thus be determined using the net present value method (see [AKKP42]). Some building components were considered for the study that are not or not widely available at the moment. These may currently be expensive due to low production numbers. For the study estimated investment costs for these products under mass production conditions have been used.
The cost-optimal component set for the new end-of-terrace example house used at first in the studies, resulted in a functional Passive House in almost all locations. At the same time minimum requirements for thermal comfort and prevention of moisture accumulation were “automatically” met. In order to test the suitability of the these component qualities for refurbishments the method was also applied to several variants of another example building which was a typical 3-storey Wilhelmenian-style residential building in a historic city quarter. For this building a full refurbishment with Passive House components (with remaining thermal bridges) as well as refurbishment with interior insulation was analyzed. In additional variants only one component was refurbished as could be the case in step-by-step renovations or if other measures are not possible because of restrictions by cultural heritage authorities. The resulting cost-optimal component qualities were often even better than for the new example building. This can be explained by the longer heating period in less efficient buildings. Thus an individual improved building component can save energy for a greater number of months every year than in a Passive House, making it even more economic to invest in better quality. As the effect was not highly significant and as it also
depends on the situation in an individual building this is not taken into account for the international EnerPHit component requirements.
As different component requirements for each location in the world would not be practical for use in general certification requirements a further step of simplification was required. Locations with similar sets of optimal component qualities were grouped resulting in 7 climate zones, with one set of component requirements for each zone (see figure 2).
The requirements for thermal insulation are naturally highest in the arctic climate zone with a maximum U-value of 0.09 W/(m²K). They are much less severe in warm and hot climate (≤ 0.50 W/(m²K) ) and tighten again in very hot climate (≤ 0.25 W/(m²K) ) where heat transmission through the opaque envelope adds to the cooling load. The requirements for interior insulation are always lower as applying interior insulation reduces the floor space, making it less rewarding from an economic perspective.
The temperature in the ground below a building or in an unconditioned basement largely depends on factors such as the geometry of the building, the characteristics of the soil and the air exchange (in basements). The temperature can be very close to the ambient air but also very close to the temperature inside the building. However, the heat loss of a building and thus the economic viability of insulation measure depend on the temperature difference between inside and outside. Thus a single U-value requirement for the basement ceiling / floor slab for all buildings would not make sense.
In the current EnerPHit criteria the U-value requirement can be divided by the reduction factor from the PHPP “Ground” worksheet in order to take the conditions in individual buildings into account. However this approach does not work for mixed climates with heating and cooling demand. Thermal insulation that helps reduce heat losses to the ground in winter also reduces heat transfer to the ground in summer, when the ground could be used as a heat sink reducing the cooling demand in moderately warm climates.
The optimal insulation level for a specific building can only be determined in the PHPP. Thus a method for calculating the insulation requirements based on project specific heating and cooling degree days against ground will be implemented in the next PHPP version. The EnerPHit certification criteria will make reference to this algorithm.
The international requirements for Passive House windows are already in use [Krick 2012] and can easily be adapted for the EnerPHit criteria. However the reduction of solar loads in cooling
climates is not fully covered by the Passive House component criteria, as they do not include measures such as shading overhangs or blinds. For refurbishment of a whole building these measures of course do have to be considered, though, in order to keep the cooling demand at an acceptable level. The solution for the certification criteria was to set a maximum level of solar loads entering per square meter of window during the cooling season. If these solar loads are above 100 kWh/(m²windowa) additional measures have to be taken to get below this value again. This could include installation of overhangs or temporary shading devices as well as anti-sun glass in hot and very hot climates. An analysis had shown that above a solar load of 100 kWh/(m²windowa) the installation of shading devices generally becomes economically viable.
The measures are only required if the building has an active cooling system. An active cooling system can be omitted if the frequency of overheating (>25 °C) does not exceed 10 % of annual hours.
For the hot and very hot climate zones additionally cool colors are required if the exterior surface is painted. These are colors which have a low absorption coefficient in the infrared part of the solar spectrum.
In the cool temperate climate the heat recovery requirement stays at ≥ 75 %. In cold and arctic climate it rises to 80 % as HRV is even more important in locations with cold and long winters. Additionally humidity recovery is required in these climates, in order to avoid very low relative indoor air humidity in winter. Alternative measures to this aim are also accepted.
In warm climates, which have neither a high heating demand nor a high cooling demand, there is not a lot of energy to be saved by heat recovery ventilation. Thus a simple extract air system without heat recovery will be sufficient. Going to hot and very hot climate heat recovery is required again, as it helps reduce the cooling demand. In hot and very hot climates that are very humid at the same time (see the hatched area in figure 2), an additional humidity recovery is required, in order to reduce the energy required for dehumidification of the supply air.
An airtightness of n50 ≤ 1.0 1/h will be required in all climate zones.
In the current EnerPHit criteria for cool, temperate climate the component requirements can be omitted, if a heating demand of 25 kWh/(m²a) is not exceeded. This principle will be kept in the international EnerPHit criteria with the requirement rising to 30 and 35 kWh/(m²a) in cold and arctic climate and going down to 20 and 15 kWh/(m²a) in warm, temperate and warm climate. In contrast to the existing EnerPHit criteria there will also be an alternative requirement for the cooling demand, which will be exactly the same as for new-built Passive Houses. An analysis had shown that in general refurbished old buildings do not need to have a significantly higher cooling demand than new-built Passive Houses if there are no exceptional difficulties.
PHI plans to put the international EnerPHit criteria into effect simultaneously with the publication of the upcoming PHPP version 9. However a draft version is planned to be published on the PHI website www.passivehouse.com before this year’s International Passive House conference. Certification of some pilot projects by PHI will already be possible based on this draft version.
The part of the development of the certification criteria, that was needed for certification of retrofits of historic buildings in the different European climates was supported by the European commission within the European FP7 project 3encult (Efficient Energy for EU Cultural Heritage“).
[Feist 2011] Feist (editor), Schnieders, Schulz, Krick, Rongen, Wirtz.: „Passive houses in different climate zones“ Passive House Institute Darmstadt, Rongen Architekten, Wassenberg, 2011
[AKKP42] Ökonomische Bewertung von Energieeffizienzmaßnahmen; Protokollband (only in German language) des Arbeitskreises kostengünstige Passivhäuser Phase V; Passivhaus Institut; Darmstadt 2013.
[Krick et.al. 2011] Krick, B., Schnieders J., Feist, W.: „Functional specifications for Passive Houses – An all-climate-definition“ In Tagungsband (only in German language) zur 15. Internationalen Passivhaustagung, Innsbruck 2011.
[Feist 2013] Feist (editor), Bastian, Ebel, Gollwitzer, Grove-Smith, Kaufmann, Kah, Krick, Pfluger Schnieders, Steiger, Theumer: „Passivhaus Projektierungs-Paket Version 8 (2013)“ Passivhaus Institut, Darmstadt 2013
[Krick 2012] Krick, Benjamin, Feist, Wolfgang: „Certification criteria and calculation regulations for Certified Passive House Components: Glazing and Transparent Components”, version 2.0, Passive House Darmstadt 2012
Overview of all articles on Passipedia about “EnerPHit – the Passive House Certificate for retrofits”
Overview of all articles on Passipedia about refurbishment
List of all released conference proceedings of the 18th International Passive House Conference 2014 in Aachen
Conference Proceedings of the 18th International Passive House Conference 2014 in Aachen