Development of a method for holistic energy renovation

During the last decade, the European Union has worked intensively to improve the energy efficiency in the building sector, aiming at liberation from the use of fossil fuels. The focus has shifted from new energy efficient buildings towards existing buildings. This implies that energy renovation likely will be intensified in the coming years.

A method for holistic energy renovation was developed that embraced the viability of the whole building renovation as well as the design of the energy saving measures. The focus was on multi-family buildings built in the period 1850-1930 with embedded wooden beams in solid masonry walls. The results indicated significant reduction of the energy usage of these buildings. This was obtained by improving the thermal performance of the building envelope and installing mechanical ventilation with heat recovery. The long-term performance of the renovation may be reduced due to mould growth behind the interior insulation or decay of the wooden beams.

The energy saving potential in two multi-family buildings was investigated by parameter studies of existing energy saving measures for both the building envelope and mechanical ventilation. Subsequently, a method was developed for a component based economical optimisation using the energy price for renewable energy as constraint. The results from both investigations showed an approximately 70% reduction for the theoretical energy usage. An economical comparison was conducted between a new building and the optimised energy renovation. The results indicated that energy renovation was beneficial compared to replacing the building.

An interior post-insulated, solid masonry wall with embedded wooden beams was investigated by two-dimensional hygrothermal simulations and full-scale measurements. Two energy saving measures were designed; one with insulation applied on the entire wall surface, and one leaving a 200 mm gap in the insulation towards the wooden beam. Risk assessment was conducted to determine the critical part of the structure. Simulation results showed that a large amount of wind driven rain and a high indoor relative humidity increased the risk for both mould growth behind the insulation and decay of the wooden beam. A small wind driven rain exposure indicated no risk regarding deterioration of the beam. This was supported by measurements. Measurements of temperature and relative humidity showed that conditions for mould growth were present.
However, no signs of mould growth were documented at dismantling of the interior insulation.

A method was developed for the design of energy saving measures based on both Failure Mode and Effect Analysis, and Limit States Design. This method was combined with the previously developed method for economical optimisation of building renovation: Firstly, the optimised combination of energy saving measures was determined. From an economical point of view the combination of energy saving measures was evaluated against replacing the existing building with a new building. Secondly, the design of energy saving measures was assessed whether to re-design, formulate a maintenance plan or assess the durability.