Benchmarking for energy efficiency

A key niche market in the low energy build sphere is the Passivhaus standard. The core focus of Passivhaus design is to dramatically reduce the requirement for space heating and cooling. The Passivhaus standard was developed in Germany in the early 1990s by Professors Bo Adamson of Sweden and Wolfgang Feist of Germany and the first dwellings to be completed to the Passivhaus Standard were constructed in Darmstadt in 1991.

Passivhaus buildings often have no traditional heating system, and instead circulate and conserve heat using whole house ventilation systems with heat recovery. This can be achieved whilst enhancing the comfort and climate of the living space. Currently, this standard is gaining in popularity in the UK, largely among self-builders, but also among an increasing number of local authority and social housing providers as a means of minimising carbon emissions from domestic buildings. A number of non-residential projects have now also been completed .

The AECB Silver and Gold standards also adopt Passivhaus principles and performance guidelines, but also incorporate kgCO2/m2 targets, with Gold being more stringent than Silver.

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Figure  Passivhaus Principles

Passivhaus involves a focus on overall energy consumption, rather than CO2 emissions. This different focus results from the heuristic assumption that it is better to avoid the need to create energy and subsequently to conserve it than it is to create it, even via low carbon means.

The Passivhaus Standards for Insulation

The Passivhaus standards for insulation, u-values, airtightness, and window performance go far beyond any criteria required by building regulations, or rewarded in the CfSH. A Passivhaus has such a highly insulated envelope that space heating requirements are greatly reduced to almost zero. This enables the designers of the building to remove the need for a formal heating system, resulting in savings that offset the additional cost of insulation and airtightness measures

The standard originated in Austria and Germany and has since become the most popular international voluntary energy efficiency standard As shown in  the standard introduces far stricter requirements on fabric performance than current UK building regulations. Further it can be shown how the alternate emphasis on energy conservation can be seen in contrast to the CO2 focus of UK building regulations. It should be noted that the annual heating load figures from the FEES and Passivhaus standard are not directly commensurate, however the Passivhaus standard is far more stringent on overall heating load requirements.

The niche nature of the standard is further demonstrated via the different assessment methodology used for Passivhaus dwellings. Whilst UK SAP 2012 has become more complex than previous incarnations and now incorporates a detailed thermal bridging calculation, Passivhaus dwellings are assessed using a far more comprehensive methodology known as the Passivhaus Planning Package (PHPP) tool.

Passivhaus Planning Package

PHPP requires many more hours of involvement from the assessor and requires a more detailed assessment of buildings idiosyncrasies, its location and orientation. This extra time investment is often crucial to delivering projects to the standard, and is reflective of the often enthusiast nature of these projects. The Passivhaus niche has also been a key driver for improving standards in the wider housing regime, with the recent inclusion of the FEES a result of niche regime interaction, whereby the UK building regulations have adopted some of the principles of Passivhaus design, at a lower level.

The Passivhaus standard has also resulted in a retrofit standard Enerphit that incorporates the philosophy of Passivhaus whilst introducing less demanding energy performance requirements. This is in recognition of the difficulty in delivering a Passivhaus in a retrofit scenario.

Table  Fabric Limiting parameters for new dwellings UK 2013 building regulations vs Passivhaus Standard

  Limiting Parameters Part L1A 2013 Passivhaus Limiting Parameters
CO2/m2 Target DER/TER=<1 N/A
Roof 0.20 W/(m2K) 0.15 W/(m2K)
Wall 0.30 W/(m2K) 0.15 W/(m2K)
Floor 0.25 W/(m2K) 0.15 W/(m2K)
Windows, Doors 2.00 W/(m2K) 0.8 W/(m2K)
Air permeability 10.0 m3 (h m3) 1.0 m3 (h m3)
Thermal bridging y= 0.15 W/(m2K) y= 0.01 W/(m2K)
Primary Energy requirement N/A 120 kWh/m2/year
Peak Heating Load N/A 10W/m2
Annual heating Load (FEES, SAP)52kWh/m²/yr. for end-terrace, semi-detached and detached houses (PHPP)2 15kWh/m2/yr.

Using the FEES conventions the 15 kWh/m2/year translates to approximately 25–30 kWh/m2/year.

SAP and PHPP use different methodologies to arrive at these figures and both are based on a different initial model of the building following different assumptions