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Does anyone offer higher savings?

After a deep retrofit, a typical apartment block from the post-war era has become a model for energy-efficient buildings. The Passive House Institute carried out scientific monitoring of the project in Giessen, Germany, and has now published its research report. The retrofit planning in advance using the PHPP tool showed a significant reduction in the heating demand. The measured data shows that indeed, energy consumption for space heating already decreased by over 70 per cent in the first year after the renovation, and even decreased by over 80 per cent by the third year. At the same time, the indoor climate improved noticeably. Deep retrofits will also take the centre stage at the 27th International Passive House Conference in April.

The housing association Wohnbau Giessen modernised a total of three buildings from the 1950s in order to significantly reduce the energy demand and noticeably increase living comfort at the same time. In one building with 12 residential units, the Passive House Institute carried out intensive measurements to investigate how successful the modernisation was. The reasons for any potential discrepancies between the advance calculations of the energy demand and the consumption values measured later should also be analysed. Through additional dynamic simulations the respective influences of the building envelope, building services and utilisation on heating energy consumption could be separated more precisely.

Excellent thermal protection

In this retrofit with Passive House components, the housing association ensured a fundamental improvement in the energy efficiency from the basement to the roof: the buildings were equipped with high-quality thermal insulation of the exterior walls, a highly insulated flat roof with a large photovoltaic system and ventilation systems with heat recovery in each apartment.

Precise calculations with the PHPP

The new windows are now triple-glazed, and the entrance as well as cellar doors are also highly energy-efficient. The basement ceilings received insulation. New front-mounted balconies resulted in reduced thermal bridges and increased living space. Heat supply via the existing district heating connection was retained. "The energy-efficient retrofit was a complete success overall, as our research results clearly show. The energy balance calculation tool PHPP had already calculated savings in the same order of magnitude as were measured later. Excellent quality and highly energy-efficient components are a prerequisite for such successful deep retrofits," explains Sren Peper of the Passive House Institute.

From 120 to 33 to 21

Before the energy retrofit, heating energy consumption in the monitored apartment building was 119.5 kilowatt hours per square metre per year (kWh/(ma)). It dropped to 33.3 kWh/(ma) in the first year after improvement of the building's energy efficiency. The tenants were already saving 72 per cent in heating energy on average. The extensive measurements carried out by the Passive House Institute show that in the third year after the retrofit, heating energy consumption was even 82 per cent lower at 21.3 kWh/(ma). At the same time, the indoor air temperatures in winter were comparatively high at 22.1 and 21.7 degrees Celsius.

Verification of deviations

Sren Peper says that with the help of the PHPP, deviations from the scheduled operation can be demonstrated in addition to the precise calculations of the future energy demand. To do this, the PHPP calculations would have to be performed using the boundary conditions existing during the measurement subsequently, such as internal heat gains and suitable climate data. Minor deviations also occurred in the Giessen apartment block, but to such a small extent that the building functioned very well after the deep retrofit.

Dynamic simulations

Concerning the dynamic simulations of the exact influence of the building envelope, building services and occupants on heating energy consumption, the Passive House Institute emphasizes that good thermal protection is essential for the building envelope, which includes insulation of the exterior walls, roof and basement ceiling as well as a reduction of thermal bridges. The building services systems, especially the ventilation system with heat recovery, also contribute greatly to the efficiency of the entire building. Ventilation units that are certified as Passive House components must also have low power consumption and must meet high requirements for sound insulation. Insulating the heat distribution pipes in the building to a high level proved critical in addition.

Influence of users

The influence of the building's inhabitants on the energy demand is also significant. If they opt for a higher room temperature of two degrees more than the average room temperature of 22.1 degrees, the heating demand will increase noticeably. However, Jrgen Schnieders of the Passive House Institute, who was also involved in the project, clarifies: "Although there is a demonstrable influence of the room temperature level on the heating energy consumption, this does not fundamentally change the positive effect of the energy retrofit. In the original state before renovating, the additional consumption due to higher room temperatures would be much greater."

Advantage in summer

Highly energy-efficient buildings also have an advantage in summer: the excellent level of thermal protection keeps the heat outside. Also users do influence thermal summer comfort in their homes. For example, it is significantly cooler inside the building if the external shading elements of the windows are deployed during hot weather and the windows are kept closed during the day, with fresh air being supplied via the ventilation system. "In this project, we were able to show what really matters when it comes to low energy consumption. If Passive House components are used, a deep retrofit of an old building like the one in Giessen can achieve the EnerPHit standard, with correspondingly low actual consumption. If a renovation is carried out as part of the usual renovation cycles, then an energy retrofit also becomes economically advantageous," concludes Jrgen Schnieders.

Focus on deep retrofits

Successful and highly energy-efficient retrofits will also be a focus at the 27th International Passive House Conference.

The leading event for highly energy-efficient construction and renovation will take place from 5 to 7 April 2024 in Innsbruck, Austria. The conference will also include a trade exhibition with Passive House components. There will be excursions to the numerous highly energy-efficient projects in Innsbruck and Tyrol on the third day.

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