Episode 110 - Retrofit using EnerPHit

This week we be talking about Retrofit using the EnerPHit standard. This episode content meets PC1 - Professionalims & PC2 - Clients, Users and Delivery of Services of the Part 3 Criteria.

Resources from today's episode:

Websites:

• https://www.passivhaustrust.org.uk/UserFiles/File/Melissa Taylor- Ecobuild EnerPHit presentation.pdf
• https://www.architecture.com/knowledge-and-resources/knowledge-landing-page/enerphit-and-the-passivhaus-retrofit-process#
• https://www.passivhaustrust.org.uk/competitions_and_campaigns/passivhaus-retrofit/
• https://www.passivhaustrust.org.uk/guidance_detail.php?gId=51

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Transcript

Episode 110:

Hello and Welcome to the Part3 with me podcast. 

The show that helps part 3 students jump-start into their careers as qualified architects and also provides refresher episodes for practising architects. I am your host Maria Skoutari and this week we will be talking about Retrofit using the EnerPHit standard. Today’s episode meets PC1&PC2 of the Part 3 Criteria.

Lets start by looking at why retrofit is important:

The built environment contributes around 40% of the UK’s total carbon footprint. The UK’s buildings currently produce 23% of our carbon emissions with 16% coming from our homes alone. Decarbonising this sector is therefore critical to achieving net zero.

While it is important to ensure our new buildings are as efficient as possible, our existing buildings are by far the biggest part of the problem. The UK has some of the oldest and least energy-efficient housing stock in Europe and 80% of the buildings that will be around in 2050 have already been built – with the majority of those built before 1990. Retrofitting some 28 million buildings is a huge challenge and we therefore need to be realistic about what should and could be achieved.

Considering retrofit within a global context, a 20% reduction in demand for new buildings by using existing structures better could save up to 12% of global emissions in the building and infrastructure sector. However, while reducing emissions is of critical importance, it is not the only reason to retrofit. A good retrofit will result in lower energy bills, better health with cold homes, summer comfort and indoor air quality all benefitting from improvement. In turn, these effects offer broader benefits to society with improved wellbeing making people happier, healthier and more productive. Retrofit plans can be integrated into existing asset management plans providing future added value for large public sector clients. This future value may be through occupant health, capital value increase and wider social value. The appraisal of social value, also known as public value, is based on the principles and ideas of welfare economics and concerns overall social welfare efficiency, not simply economic market efficiency. Adopting these approaches can improve quality of life, deliver more homes, and retain cultural heritage and community ties as well as avoid carbon-intensive and costly demolition and rebuild processes.

Now lets look at what EnerPHit is and how it can assist with retrofit:

The building physics principles behind Passivhaus apply to any building – but you may not be able to get quite the same results from an existing building where you aren’t really in control of the building’s orientation, structure, shape or amount of glazing. The Passivhaus standard, therefore, includes a retrofit standard called EnerPHit which takes these limitations into account and relaxes some criteria to reflect this.  However, it is still a very demanding standard and will typically result in a building that outperforms a new-build property both in terms of energy and comfort.

EnerPHit was introduced to the UK in 2010 and its aim is to create a standard for an economically and ecologically optimal energy retrofit for old buildings that can’t achieve the Passive House Standard with reasonable effort. It is essentially an approach that can be applied to any retrofit project and it uses passive house components to achieve a quality-approved energy retrofit. So you follow the Passivhaus process and within that the EnerPHit standard. 

Where projects adopt the EnerPHit standard they will also benefit from the performance assurance provided by the EnerPHit certification process. Any approach which does not include EnerPHit certification should be augmented by an additional and appropriate quality assurance mechanism.

To demonstrate how a refurbishment meets the relevant criteria to achieve EnerPHit will require an energy balance calculation using PHPP and the certification is only provided in circumstances where modernisation to Passivhaus level would not be practicable or cost-effective. A key item to highlight is that EnerPHit doesn’t apply for the warm, hot and very hot climate zones, its more suitable for colder climates.

So what are the steps in achieving EnerPHit and what does it deliver:

A radical whole-house retrofit is likely to achieve the best results both in terms of energy reduction and comfort. However, this is a significant undertaking which could take place over several years. Getting the sequence right and decisions in the early phases are critical to ensure that the full potential of the retrofit is realised and that the project doesn’t inadvertently result in ‘carbon lock-in’. The EnerPHit process, therefore, includes tools to structure the retrofit in a step-by-step way, helping to ensure that the implications of each step are understood and properly planned out right at the start of the project.

High-quality deep retrofits deliver:

• Reduced fuel bills
• Improve health and wellbeing outcomes
• Optimised buildings to decarbonise the grid
• Reduce carbon emissions
• Reduce demand for renewable energy
• Reduce peak load 

Taking all these factors into consideration, the Passivhaus Trust recommends an EnerPHit informed Retrofit Plan (EiRP) is created for all retrofit projects. This will create a whole building retrofit plan that allows all retrofits to benefit from the advantages of the EnerPHit methodology. This includes modelling the existing building in the Passivhaus Planning Package (PHPP) to provide detailed calculations of the existing fabric performance of the building, which provides a base from which various upgrade options, including a range of energy performance targets, can be tested as part of an options evaluation process. Deep retrofit works, to the EnerPHit standard, result in an 80% reduction in the additional demand on the grid. 

EnerPHit uses the same set of criteria as for Passivhaus Classic new build, but with a small relaxation for certain criteria. These criteria include:

• Space Heating demand: of equal or less 20, or 25 or 30 kWh/m2a(annum) which is between 5-15 higher compared to the Passivhaus classic new build
• Primary Energy Demand: of equal or less 135kWh/m2a(annum) which is equal to to the Passivhaus classic new build standard
• Primary Energy Renewable: of equal or less 71 for Cool temperature or 65.5 for warm temperature which is about 5-11 higher compared to the Passivhaus classic new build 
• Airtightness: to be equal or less of 1 ach (air changes) @ 50Pa (pascals) which is about 0.4 higher compared to the Passivhaus classic new build
• Summer overheating: to be maximum 10% at over 23 degrees which is equal to the Passivhaus classic new build
• Surface temperature: to be over 17 degrees which is equal to the Passivhaus classic new build
• Ventilation: to be 30m3/hr.person (cubic meters per hour) which is equal to the Passivhaus classic new build

The EnerPHit space heating criterion target depends on the climate zone. The UK spans three climate zones, but the majority of the country is classed as cool temperate and thus EnerPHit will typically deliver a space heating demand of 25 kWh/m2.year. The majority of the other criteria are the same as for Passivhaus Classic with the exception of airtightness which is relaxed from 0.6 ACH@50Pa to 1.0 ACH@50Pa. Thus, if we consider EnerPHit in the context of the UK stock, it will result in a retrofitted building which has a space-heating demand 80% lower than the national average.

The EnerPHit standard can also be achieved via the component approach. This doesn’t refer to certified Passivhaus components, but rather to the component parts that make up the building – i.e. walls, roofs, floors, windows and doors. Rather than set a specific space heating demand target, this alternative approach sets limits for the thermal performance of the building elements alongside the same targets for airtightness, ventilation and surface temperatures. The reason for this option is to cater for buildings where the orientation, form factor and glazing preclude achieving the required space heating demand, even when the fabric has been upgraded to levels corresponding with Passivhaus performance.

Apart from EnerPHit there are also a number of other retrofit standards, which I though migh be useful to share, some these are:

The AECB (Association for Environment Conscious Building) and LETI have both their own retrofit specifications. Both have been derived from the views of experienced practitioners who have been undertaking deep retrofit in the UK for some time. Their targets are chosen to deliver a good depth of retrofit which is both feasible and affordable for most UK homes and could also be achieved at scale. The AECB offer a retrofit standard which can be certified against, whereas LETI are simply offering guidance to support a good level of retrofit. For this reason LETI strongly recommends that a recognised retrofit standard and quality assurance process is used alongside the LETI guidance. EnerPHit retrofits achieve reductions aligned with LETI’s exemplar targets in terms of retrofit ambition. 

Then there is the PAS 2035 Retrofitting dwellings for improved energy efficiency – Specification and guidance which is a framework and guidance document for delivering retrofit projects, published by the British Standards Institute (BSI). It promotes a fabric-first, whole house approach. It focuses on proper retrofit planning and quality assurance and requires the appointment of accredited professionals - including a Retrofit Coordinator - to oversee the retrofit project. PAS 2035 does not set energy efficiency targets or define how ‘deep’ one should go with the retrofit. Its aim is to avoid the unintended consequences, defects and performance gap of poor retrofit. All retrofit projects receiving central government funding are required to be PAS 2035 compliant. PAS 2035 works in tandem with the PAS 2030 standard for the installation of energy efficiency measures in existing buildings. Taken together, PAS 2030 and PAS 2035 lay down the steps domestic retrofit projects can follow to gain compliance and ensure consumer satisfaction in accordance with the recommendations of the Each Home Counts review. 

The LETI specification also includes guidance for a component approach where, similar to the EnerPHit component approach, elemental u-values are specified. However, unlike EnerPHit, the aim of this alternative is to provide practical guidance for retrofits where detailed PHPP modelling will not be undertaken. There are parts of the AECB Retrofit Standard, such as the approach to moisture risk, that the Passivhaus Trust recommend is applied to all retrofit projects. The AECB run a Carbonlite Retrofit Course, developed specifically for the UK, that gives construction professionals an understanding of retrofit that can be applied to all the approaches discussed, and provides valuable tools to avoid or manage unintended consequences. This course is recognised by the International Passivhaus Institute. The AECB Retrofit Standard is also complemented by the AECB water, daylighting and lifetime carbon standards.

Now lets look at the performance gap in retrofits:

The energy performance gap in new-build homes is estimated at 60% additional space heating demand. The root causes of the new-build performance gap all apply to retrofit. But there is less regulation in the retrofit sector and the contractors completing this work will tend to be smaller with fewer specialist skills. The retrofit performance gap is therefore likely to be even more significant than in the new-build sector. As has been demonstrated in several studies, the Passivhaus approach effectively closes the energy performance gap using a combination of rigorous design, demanding criteria and an independent certification process. 

However, the performance gap in retrofit is far wider than energy. It also encompasses moisture. A good retrofit is one that avoids all unintended consequences. Many of the principles of Passivhaus can help achieve this, including quality control, airtightness and continuous insulation. To ensure good moisture design it is recommended that all retrofit projects incorporate a moisture risk assessment, and similarly, to maximise summer comfort, a summer overheating stress test should be incorporated into the design process.

Now lets look at a quick comparison of the different retrofit approaches mentioned earlier:

First looking at farbic performance:

• All three EnerPHit, AECB and LETI provide a space heating demand limit

Then looking at the overall limit on energy demand and emissions:

• EnerPHit allows for Primary Energy or Primary Energy Renewable limit
• Whereas AECB has no limit for overall energy demand but direct electric and new gas boilers are not accepted
• And LETU provide for hot water demand limit and overall energy use intensity limit

Then we have comfort and health:

• EnerPHit provides for surface temperature and summer overheating limits as well as ventilation rate minimum and an airtighness limit
• AECB offer the same with the addition of reduction of moisture and mould and evaluation of radon
• LETI only provide for an airtightness limit

And lastly is closing the energy performance gap:

• EnerPHit addresses it via the use of PHPP modelling, avoidance of thermal bridges and airtightness and independent QA process
• AECB offers the same with the addition of having qualified people undertaking the works and testing
• And LETI does not address this element

This demonstrates that while all approaches have criteria aimed at improving fabric performance, the supporting criteria to drive overall energy reductions, comfort and health outcomes, and closure of the performance gap are less consistent and should also be considered. This also shows that all approaches require some augmentation to deliver robust solutions addressing all aspects of the retrofit performance gap and unintended consequences. Common to all approaches is a requirement to augment with additional summer overheating stress testing, which should be undertaken for all retrofit projects in the UK. The AECB standard is a holistic standard, covering a range of retrofit specific challenges, this includes, flood, fire and heritage risk evaluation. The AECB Carbonlite Retrofit Course also covers constraints for existing buildings in retrofit design, set within the context of the UK building stock.

Where we might end up with a retrofit depends to a certain extent on where we are starting from. Understanding where this might be is by no means straightforward as the UK’s regulatory instrument (the EPC) does not provide us with detailed information about the actual energy performance of buildings. Space heating demand is a key Passivhaus criterion and is a good proxy for a building’s fabric performance. The Passivhaus Trust have worked with LETI to build a stock model of the UK’s existing domestic buildings, which has been used to model the space heating demand profile of the UK’s homes, broken down by building form.

On average UK space heating demand is around 120-130 kWh/m2.year with a spread from 80 to 190 kWh/m2.year. In comparison, a typical UK new build (Building Regulations 2020) has a space heating demand of 85 kWh/m2.year. The spread of retrofit targets discussed shows the space heating demand criterion for each. This shows that for an average home to reach EnerPHit levels, an 80% reduction is required. For the component approach, this averages 72% and for the AECB/LETI criterion, it averages 60%.

Taking all these factors into consideration, the Passivhaus Trust recommends an EnerPHit-informed Retrofit Plan is created for all retrofit projects. This will create a whole building retrofit plan that allows all retrofits to benefit from the distinct advantages of the EnerPHit methodology. This includes modelling the existing building in the Passivhaus Planning Package (PHPP) to provide detailed calculations of the existing fabric performance of the building, which provides a base from which various upgrade options, including a range of energy performance targets, can be tested as part of an options evaluation process. Where projects adopt the EnerPHit standard they will also benefit from the performance assurance provided by the EnerPHit certification process. Any approach which does not include EnerPHit certification should be augmented by an additional and appropriate quality assurance mechanism. All approaches to retrofit, including EnerPHit, require some augmentation to deliver robust solutions addressing all aspects of the retrofit performance gap and unintended consequences.

To sum up what I discussed today:

• There are many issues surrounding retrofit at scale in the UK. The Passivhaus standard, therefore, includes a retrofit standard called EnerPHit which takes the limitations of retrofit into account and relaxes some criteria to meet Passivhaus standards for retrofit.
• A radical whole house retrofit is likely to achieve the best results both in terms of energy reduction and comfort. The EnerPHit process, therefore, includes tools to structure the retrofit in a step-by-step way ensuring that the implications of each step are understood and properly planned out right at the start of the project.
• The EnerPHit standard can also be achieved via the component approach which refers to the component parts that make up the building – i.e. walls, roofs, floors, windows and doors. The reason for this option is to cater for buildings where the orientation, form factor and glazing preclude achieving the required space heating demand.
• Alongside EnerPHit, the AECB (Association for Environment Conscious Building) and LETI have both their own retrofit specifications. And also the PAS 2035 Retrofitting dwellings for improved energy efficiency – Specification and guidance which is a framework and guidance document for delivering retrofit projects, published by the British Standards Institute (BSI).
• All approaches to retrofit, including EnerPHit, require some augmentation to deliver robust solutions addressing all aspects of the retrofit performance gap and unintended consequences.