Innovation & Cost efficiency: Building standards for multi family residential buildings at optimal cost (Inno-Cost)
With the recast of the EPBD of 2010 (European Performance of Buildings Directive, 2010/31/EU) cost efficiency has become a key aspect for the definition of minimum energy performance requirements of buildings. EU Member States shall set their minimum requirements for the thermal quality of the building envelope and the technical building systems in such a way that construction and operation cost of buildings is cost-optimal over the estimated economic lifetime.
With regard to the requirement that all new buildings have to meet nearly zero-energy standard from 2021 onwards, cost efficiency and affordability of innovative building concepts become key topics. Surprisingly economic analyses over the whole life-cycle of energy-efficient buildings have been performed only partially. To date no broadly based studies which analyse cost efficiency of innovative building concepts on the basis of measured data exist.
Contents and Objectives
The main objective of this project is to analyse innovative building concepts with regard to their economic performance over the life-cycle of the building. The life-cycle cost of a representative sample are calculated and evaluated for the first time. The sample consists of about 100 large energy-efficient residential buildings.
The analysis is based on measured consumption data and cost of the operated buildingsThe calculation results form the basis for the assessment of the cost efficiency of innovative building concepts, and present evidence for needed framework conditions for a further market diffusion of innovative building standards and reveal fields where further research is needed. For builders the results shall provide orientation for the actual planning and realisation of future innovative projects.
A survey gathering energy consumption and cost data of large energy-efficient residential buildings (new and existing) has been carried out with builders. Operated buildings that feature a heating demand of less or equal 50 kWh/m2a were taken into account. This data built the basis for the life-cycle cost analysis. The survey, for which a new questionnaire has been developed, was conducted in cooperation with the Austrian Federation of Limited-profit Housing Associations (gbv).
The data collection contained building data, data about the technical building systems, energy consumption and energy cost, solar yield of the solar thermal system, auxiliary energy, as well as cost for maintenance and for construction of new construction or renovation. The gathered data for each object was validated and cleansed. The effort for collecting the data was far greater than expected both for the companies and for the project team, because currently only a few builders have implement standardised monitoring systems for energy consumption and costs.
The gathered data represents a sample of about 100 objects, for which plausible data sets for measured energy consumption for several years of operation and cost data are available. Most of the objects have been finished between 2006 and 2010 (either newly constructed or renovated). The sample includes objects from all states except Burgenland. Regarding the A/V ratio and the number of housing units per building the sample represents the whole range of large volume residential buildings in Austria.
The measured energy consumption data was divided into energy consumption for heating and for domestic hot water and was clustered according to heating demand categories. The correlation between actual consumption and heating demand of the buildings was assessed. The yields of the solar thermal systems were also taken into consideration as part of the assessment of energy consumption.
The gathered cost data for energy and maintenance was analysed and benchmarked for the individual energy carriers. Cost data for construction cleansed in several steps. Total cost consisting of cleansed construction cost and running cost built the basis for the life-cycle cost analysis.
The net present value method was chosen for the life-cycle cost analysis of the total cost. Total cost was established by means of two different procedures. In procedure 1 the cost optimal level was derived from the extreme of a polynomial function while in procedure 2 the cost optimal level was derived from heating demand categories. Several scenarios with different framework conditions were calculated to achieve durable results.
Finally, the cost-optimality calculation was conducted according to the methodological framework of the EU (Delegated Act 244/2012) for different energy-efficiency standards. A typical reference building was determined, 13 variants for the building envelope and the building systems were defined and framework conditions set. The energy demand was calculated according to the method of the energy performance certificate. Additionally the trend model found in the evaluation of surveyed data was used to calculate energy consumption was used as a comparative analysis.
The analysis reveals a distinct correlation between the measured energy consumption and the respective heating demand category. In average innovative nearly zero-energy buildings feature a lower energy consumption in reality compared to buildings with HD 50. The trend line between HD 50 and HD 10 (planned) reveals a reduction of the average measured heat energy consumption by a factor of 2 (from 60 to about 30 kWh/m2a).
Within the specific heating demand categories the energy consumption of buildings scatters significantly. For both low-energy and nearly zero-energy buildings the measured energy consumption data displays a broad range. The lowest and the highest value of a HD category differ in average by a factor of 3.
Surveyed energy tariffs of individual objects vary tremendously and therefore have a large impact on energy cost. Besides energy cost also maintenance cost are an important cost factor. Maintenance cost imply a considerable potential for cost reduction. There is a tendency that lower energy cost are compensated by higher maintenance cost and electricity cost for the ventilation system in particularly energy-efficient buildings.
The cost optimality calculation for a period of 30 years results in minor cost differences between different energy-efficiency standards. This result is in line with other studies. Current minimum energy performance requirements are located in the cost-optimal level. However a moderate strengthening of the requirements towards the cost optimum is feasible.
Innovative building standards can only be cost efficient if the proposed heating demand levels are reached in practice and if maintenance of the building technology is provided at optimal cost. The compliance of energy consumption with energy demand levels depends on several parameters, which are: Validity of the calculation, quality assurance over the whole planning, construction and commissioning process as well as user behaviour.
Due to the significant scattering of data it is questionable to draw general conclusions for the profitability of building standards on the basis of data of individual objects.
For a further propagation of innovative building concepts additional impulses for quality assurance over the whole planning, construction and commissioning process as well as during operation are necessary. A moderate tightening of the current minimum energy performance requirements with respect to the 202020 goals is feasible also from the economic point of view. Affordable solutions for a continuous and standardised energy consumption and cost monitoring systems are an important aspect of quality assurance.
The results are a guide to define which incentive systems will facilitate the further propagation of innovative building standards best. Future incentive systems should be strongly oriented on quality assurance and should require continuous energy monitoring systems as a mandatory element for the eligibility for funding.
Prospects / Suggestions for future research
The analysis contains data of existing innovative buildings with an age of 5 to 10 years, which belong to the “first generation” of low-energy and nearly zero-energy buildings. In the meantime additional know-how was gathered and technological development, especially with respect to cost-efficient solutions, has taken place. Therefore an ongoing data analysis with data from new buildings is essential.
Quality assurance plays a key role for the propagation of innovative technologies. The central tool of quality assurance is a detailed energy consumption and cost monitoring.
Research and development activities should therefore focus on standardised and affordable monitoring solutions on the one hand. On the other hand detailed energy consumption and cost monitoring systems together with an economic assessment should be applied in future pilot- and demonstration projects.
DIpl.-Ing. Walter Hüttler, e7 Energie Markt Analyse GmbH