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  What's is a passive house Retrofit?
 

To meet the UK's target of an 80% reduction in carbon emissions by 2050, we must dramatically improve the performance of existing UK housing stock. Housing in the UK accounts for 27% of carbon emissions and at least 60% of the houses which will be in use in 2050 have already been built.

Improving the overall efficiency of a nation's housing stock by insisting new buildings reach the impressive passive house standard can mean a 90% energy saving and a high level of thermal comfort.

In many UK energy consumption for housing heating and domestic hot water causes around one 30% of CO2 emissions. For this reason the reduction of energy demand from buildings plays an important role in efforts to control greenhouse gas emissions.

Measurements, in several hundred different types of accommodation, show energy consumption in new houses can be reduced drastically. For instance, while a typical new single family house in the UK  has a specific space heat demand of 120 kWh/m2 of floor area (a), the demand of a so-called ‘passive house retrofit standard ’ is 25 kWh/m2 a or less.

In Austria the number of new passive houses has grown significantly as a percentage of overall house building. More than 2000 passive houses have been erected in the last decade. In Vienna, large settlements are to be developed to passive house standard, and in the region of Vorarlberg in western Austria, social housing companies have been obliged to build to passive house standard since 2007. More recently, a broader spread of building types has been realized in passive house-standard, including office buildings, schools, kindergartens, super-markets and others. Both the German and Swiss markets are seeing similar developments too, and while passive house was a standard mainly limited to the German-speaking countries initially, the past five years have seen it begin to spread across Europe. This was partly due to European research and development (R&D) projects such as the Promotion of European Passive houses (PEP) programme or the Passive On Programme.

Today, ‘passive house’ is a clearly defined standard across most of Europe for buildings of a very high energetic performance. Experience has shown that a single definition of the passive house can be used at least from 40°–60° latitude, and passive house definition has been tested in both Scandinavia and southern Europe. Key parameters are a specific space heat demand maximum of 15kWh/m2 a, a specific primary energy demand for space heating, cooling, domestic hot water, electricity for pumps and ventilation and household appliances at a maximum of 120 kWh/m2a, a maximum heat load of 10 W/m2 a, and an airtightness of n50 0.6/h maximum

 
 
Retrofitting Passive House Components
 
Although the successful implementation of passive house standard in new buildings plays an important role in the overall strategy to reduce greenhouse gas emissions, the improvement of the energy efficiency of the existing building stock is of even bigger importance. In Austria, the yearly rate of new built apartments is about 1% of the existing building stock. Depending on age and building type, the specific space heat demand is 130–280 kWh/m2. As only about 1%–1.5% of the building stock is retrofitted per year and this rate cannot be increased to much more than 2.5%, the improvement of the energy efficiency quality of retrofits is essential in order to reach the national, European and international targets for the reduction of greenhouse gases.
However, since 2001, more and more renovations in Austria, Germany and Switzerland have been carried out using components that had previously been tested in new passive houses. Different names are used for these houses, sometimes called ‘factor 10-houses’ as the energy demand after renovation is only a tenth of the original demand.

In these projects, a specific heat demand after renovation of 23 kWh/m2 a, was achieved.

The main elements of the energy concept are typical passive house components:

•Excellent insulation level of opaque building elements: u-values range from 0.10 W/m2K for walls and roof to 0.18 W/m2K for basement ceilings.
•Triple glazed windows with adequate frames and an optimized installation.
•Thermal bridges reduced to a minimum.
•The airtightness was improved by a factor of 6–10, the limiting value for new passive houses was achieved.
•A ventilation system with highly efficient heat recovery installed.
•Thermal solar collectors installed covering up to 60% of the annual energy demand for domestic hot water.
•Highly efficient condensing gas boilers were installed; where possible, ducts have been insulated to a very good level; in other projects biomass boilers have been successfully tested.

 
Benefits of the Retrofit Programme
 

Experience with the renovations up to passive house standard is so far very good in the Vorarlberg projects, as well as in projects in other regions of Austria, Germany and Switzerland.

Thermal comfort has been improved to a level superior to that of a conventional new house; due to the ventilation system the air quality is improved, and energy bills are reduced drastically. As thermal bridges are minimized, the airtightness is significantly improved and the air exchange is always up to hygienic standards due to the ventilation system; the main causes for structural damage and mould problems are also eliminated.

Furthermore, the measured energy consumption shows good comparison to the demand that was calculated in advance using the passive house planning package (PHPP).

Austrian and German research has shown that for bigger apartment buildings renovations to passive house standard or very close to it cost about €450–600/m2a. The extra cost compared to a renovation up to national building code is in the range €80–150/m2a.

For comparison a new apartment building costs about €1600/m2a in western Austria.

Nonetheless, detailed analyses show that most of the measures used in passive house retrofit are economically feasible, for example, the overall lifecycle cost for investment and energy is lower using the passive house insulation of 26 cm compared to the building code insulation of 12 cm. As for most renovations lifecycle costs are not calculated, home owners and housing companies tend to realize sub-optimal insulation thicknesses, for example.

In some regions of Austria, the regional funding system therefore differentiates the rate of funding according to the energy efficiency quality of the house after renovation – the lower the energy demand, the higher the funding. The experience in Austria, with nine different funding systems in its nine regions, shows that this funding rate differentiation is an effective way of encouraging very high quality standards.

 


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