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building stock of Denmark implies that it is economically beneficial to renovate the buildings built in the period 1850-1930. In the extrapolation, the energy consumption is not necessarily reduced to the extent given in this example (ca. 70%) due to the small influence of energy consumption on the overall economic viability of the retrofit.

5.2 Design of energy saving measures

In Paper IV the design of a post-insulated solid masonry wall with embedded wooden beams was investigated using FMEA. The FMEA method was time-consuming and it only provided little, if any, new knowledge regarding the failure modes. This, however, may be the case when working with well-know energy saving measures. In the process of developing energy saving measures, the FMEA clarified the potential of identifying failures and effects that needed further investigation.

Furthermore, the FMEA identified the risk of deterioration of the beam and mould growth behind the insulation as a consequence of interior insulation.

5.2.1 Risk for deterioration of wooden beam

The risk for decay of the wooden beam embedded in solid masonry is investigated by hygrothermal simulations and full-scale measurements. These results show that installing interior insulation on the solid masonry wall changes the moisture balance in the wall. This is a result of the reduced drying potential to the inside due to placement of a vapour barrier on the inside of the insulation. Also the amount of wind driven rain significantly influences the durability of the wooden beam.

In Paper IV it is shown by changing the rain exposure coefficient that the wind driven rain has large influence on the moisture performance of the reference structure.

The reference structure exceeds the moisture content limit, 0.2 kg/kg, for wood decay at rain exposure coefficients above 0.3, which is interpreted to be a lower amount of rain. Two additional simulations to Paper IV were performed for a structure without a gap in the insulation:

1. Without wind driven rain.

2. Without wind driven rain and 80% relative humidity in the indoor environment.

The first simulation shows that a low rain exposure coefficient (0.1) almost corresponds to the case without rain. The second simulation shows that the increase in relative humidity has minor influence on the moisture content in the beam. The two additional simulations show that the moisture environment around the beam is highly influenced by the moisture environment outdoor and indoor in terms of the amount of wind driven rain and relative humidity, respectively.

The amount of wind driven rain depends on the location of the building and macro- and microclimate surrounding the building. The simulations are performed using a reference year. However, the reference year does not include extreme rain events occurring e.g. every 50 years. It is very important to take extreme rain events into

5 Discussion 5.2 Design of energy saving measures

50 Technical University of Denmark

extreme rain events is important if trends in the hygrothermal response of the wall assembly are at the critical limit for onset of mould growth or wood decay.

The measurements in Ryesgade were performed in the northeast facing wall between ground floor and first floor. Given the urban area, the orientation and location of the building, the exposure of wind driven rain and direct sunlight is expected to be limited. It is expected that the risk for deterioration of the beams is at a minimum based on the simulation results and the expectations regarding wind driven rain and direct sunlight. The 200 days of measurements show values 5-10% relative humidity higher in the beam, when the wall was insulated as compared to an uninsulated wall. This indicates that the interior insulation may have changed the moisture balance around the beam. Continuous measurements are likely to reveal whether risk likelihood increases or not.

A way to counteract decay of the wooden beams is to stop the interior insulation 200 mm above the floor. Simulations show that the heat loss from the floor division is sufficient to heat up the beam and avoid decay. In that case, the moisture content of the beam is similar to the moisture content of the rest of the structure. However, the risk of mould growth is high in the 200 mm gap.

The hygrothermal simulations are not validated by means of the measurements.

Nevertheless, both the simulations and measurements shed light on the risk for deterioration of the wooden beam and the onset of mould growth behind the interior insulations.

5.2.2 Risk for mould growth behind insulation

Interior insulation is often associated with risk of mould growth and specifically in the presence of organic material. The mould growth depends on several other factors, where the most important factors are temperature, relative humidity and exposure time.

The moisture condition of the masonry-insulation interface is, like the wooden beam, influenced by the wind driven rain. Applying interior insulation on the entire wall surface the relative humidity increases above critical threshold value. In the case with a gap in the insulation, the relative humidity is significantly lower in the corner of the gap and the temperature was higher. The lower relative humidity and higher temperature are at the place where the insulation ended, see Figure 4.7. The additional simulations to Paper IV show an increase in relative humidity in the masonry-insulation interface. Especially, regarding the relative humidity it is important to determine the material parameters of the air/vapour barrier to limit the risk of convection and diffusion of humid room air into the wall.

In the Ryesgade case, the measurements initially showed high relative humidity.

This may, however, be due to built in moisture from mounting of the sensors. The sensors were placed in a critical area for mould growth. After dismantling the insulation, the visual assessment of the area and the Mycometer surface test revealed no signs regarding mould growth. This may be due to the insulation was glued onto the wall resulting in no convection behind the insulation. Furthermore, the wall

5.3 Holistic energy renovation 5 Discussion

surface was cleaned and tested with Mycometer surface test for organic material before mounting the insulation. In the apartment below the test apartment, insulation was installed directly onto the wallpaper implying extensive mould growth. However, the relative humidity and temperature was not measured for this wall. Nevertheless, this highlights the need for cleaned surfaces with respect to organic material before installing before interior insulation.

5.2.3 Method for design of energy saving measures

In Paper IV, the investigation of energy saving measures using FMEA and hygrothermal simulations concludes that FMEA is very time-consuming.

Furthermore, the gain of new knowledge is limited for the masonry wall with embedded wooden beams. The FMEA provides a thorough hazard identification of the potential failure modes. However the method has to be combined with other methods to assess durability issues. The durability evaluation is possible by use of the Limit States method.

The developed method presents a framework for evaluation whether to re-design the structure, formulate a maintenance plan or check the durability. In the proposed method, the main disadvantages of FMEA, the huge time-consumption and the need for an expert group, are eliminated by identifying the boundary conditions and transfer mechanism. The rating of severity, occurrence and detection becomes a tool in the evaluation of the action to take regarding re-design, maintenance and durability.

The method does not unambiguous clarify whether the need is for maintenance planning or durability assessment. Thus it is up to the designer to evaluate the given situation based on his knowledge, experience and information provided from the risk assessment. The decision may relate to the economical aspect which is not included in the method. The need for a human assessment combined with risk assessment may minimise the risk of deficient solutions to the problem. The energy saving measures should be developed with the function, energy savings, and durability ensured for lowest overall cost.

5.3 Holistic energy renovation

In the content of holistic, from building to measure, energy renovation, the two developed methods constitute a two-fold framework. Firstly, a component-based economic optimisation of the whole building followed by an evaluation whether to renovate the building or demolish and build new is conducted. Secondly, the design of the energy saving measures is thoroughly investigated for maintenance and durability.

The method is an iterative process in case the assumptions regarding maintenance and energy consumption change due the design of the measure.