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We Need A Definition of Nearly Zero Energy Buildings

Low energy house types in Europe

A selection of low energy building types in Europe.

Most of the buildings around now will still be here in 2050, so the real challenge is not only making new buildings energy efficient but eco-renovating the old ones.

A new analysis of different pathways to achieving this goal has identified the most cost-effective ones, depending upon the existing housing stock. Although the study is focus on the different member states of the European Union, it could be applicable elsewhere that buildings and climate are similar, since the range of both within Europe is large.

The message is that while a strengthening of regulatory measures is essential, what is really crucial is a much stronger focus on compliance with regulations.

In most cases nobody ever bothers to check whether building regulations have been complied with, let alone conducts post-occupancy evaluations to see whether the expected performance is achieved.

The study uncovers a huge lack of data regarding renovation activities and the energy performance of buildings and calls for a building data observatory, in particular for monitoring the impact of policies.

It finds that the European Energy Performance of Buildings Directive (EPDB) has not performed as well as expected, even in the recast version. 

The EPDB requires that from 2019 onwards all new buildings occupied and owned by public authorities in Europe are nearly Zero Energy Buildings (nZEBs) and that by the end of 2020 all new buildings must be nZEBs.

But because there is a wide variety in building culture (including ownership) and climate throughout Europe the Directive doesn't prescribe a uniform approach. Instead it asks member states to draw up specific national roadmaps that reflect their national, regional or local conditions.

Chart of European building stock by country and age:

Graph of European building stock by country and age

It's necessary to deeply renovate the existing building stock to highly ambitious levels, in line with long-term energy policy and climate mitigation targets. 

But the problem is that the Directive does not contain a clear definition of nZEB renovation.

This study, Laying down the pathways to nearly Zero-Energy Buildings, A toolkit for policy makers, undertaken by ENTRANZE (Policies to Enforce the Transition to nearly Zero-Energy Buildings in the EU-28), attempts to find policies to fill this gap.

According to the ENTRANZE model results for EU-28, the current policy framework could lead to savings of about 20%-23% of final energy demand from 2008-2030. In contrast, more ambitious policies, as developed during this project in extensive discussions with policy makers, would lead to savings of 29-31% in final energy demand.

However, this still does not represent the maximum of achievable effort and policy innovation. Almost half of the final energy demand for heating and hot water is covered by natural gas in 2008.

The research shows that an ambitious policy package could reduce natural gas demand in 2030 by almost 36-45%, potentially halving energy dependency on gas in the building stock by 2030.

The study says that the EPBD needs to make clear that cost-effectiveness must stand as the absolute minimum requirement for existing relations in building codes, and that current activities to improve high quality renovation, that would result in substantial savings, have to be significantly increased to have a lasting impact.

"While nZEB's energy performance level should be cost effective they still have to be more ambitious than cost optimal energy performance levels," the report says.

Chart of cost-optimal building eco-refurbishment in Europe:

Chart of cost-optimal building eco-refurbishment in Europe

It argues that European member states must be challenged to close the gap between the requirements of nZEB targets and the cost of the less stringent levels of current building codes. It should then gradually increase the requirements of the targets for existing buildings and for this a clear definition of "deep renovation" or nZEB is required.

There is also some confusion with standardisation and terminology.

Single family houses show the most potential for the use of renewable energy technologies is more effective in Mediterranean climates (characterised by higher solar radiation). A similar trend applies to office buildings, but with fewer differences between the South and North of Europe because of the higher electricity consumption for auxiliary systems and mechanical ventilation.

Net primary energy saving percentages for cost-optimal and nZEB targets are closer together in residential buildings than in office and school buildings. Multi-family dwellings show lower energy saving potential compared to single houses, due to geometric limits, such as the lower available roof area for solar systems.

Three tools

Part of the problem that the study attempts to tackle is the high initial cost of a deep renovation compared to the energy saving over 30 years. The study uses three tools to analyse this:

  • The Data Tool: an in-depth description of the characteristics of buildings and related energy systems in the EU-28 and Serbia.
  • The Cost Tool: ia powerful, flexible instrument to analyse the impact of a large number of renovation packages for specific building types in terms of costs and primary energy demand.
  • The Online Scenario Tool: the results of alternative scenarios for the development of the building stock and its energy demand in the EU-28 (+ Serbia) up to 2030.

It concludes that while measures required to achieve nZEB-levels may not be cost-effective today, by 2020 they could be. this is especially true of using renewable energy systems for heating and cooling.

Perhaps its most valuable contribution is a country-by-country analysis and set of recommendations. For instance for France it says that:

"Despite five updates of building codes since 1974 for new construction and the fact that the last building code implemented (RT2012) is one of the most stringent in EU29, the specific energy consumption per m² and per heating degree days in buildings in France is still significantly higher than in other EU countries."

The study builds on an earlier one on the definition of nZEBs, concluded in 2011, which just goes to show how regrettably slow movement is on this topic.

This study found that:

"typically, low-energy buildings will encompass a high level of insulation, very energy efficient windows, a high level of air tightness and natural/ mechanical ventilation with very efficient heat recovery to reduceheating/cooling needs.

"Passive solar building design may boost their energy performance to very high levels by enabling the building to collect solar heat in winter and reject solar heat in summer and/or by integrating active solar technologies (such as solar collectors for domestic hot water and space heatingor PV-panels for electricity generation).

"In addition, other energy/resource saving measures may also be utilized, e.g. on-site wind turbines to produce electricity or rainwater collecting systems."

Yet, it found that in 2011, more than half of the Member States did not have an officially recognised definition for low or zero energy buildings.

Four years later the situation is not much better.

David Thorpe is the author of