Primary Energy Renewable and future climate Impact on buildings
Jessica Grove-Smith is senior scientist and joint managing director of the Passive House Institute in Darmstadt. Her areas of expertise include energy efficient building solutions to the Passive House Standard around the world, interrelations between efficiency and renewable energies (the PER concept) and deep energy efficiency for public indoor swimming pools. Jessica frequently participates in conferences internationally on technical and policy related topics with regard to high performance buildings.
1. Before discussing about future scenarios and renewable energy sources in Passive House (PH) constructions, can you share some figures on where the development of PH standard is today:
What is the current uptake of the PH standard and certification outside Europe? /in other climate regions, different from the central and northern Europe ones where this standard originated?
Passive House is rapidly increasing in popularity in many parts of the world. At the start of this year, we recorded over 29,000 units certified to the international Passive House criteria, which equates to more than 2,7 Mio m² living area the world over. Of course, this only includes the certified projects, as we don’t have figures of the number of non-certified projects built based on the Passive House concept. Though we encourage building owners to certify their Passive House buildings as a quality assurance measure.
To help log projects, we have the online Passive House Project Database, which is constantly growing and provides useful insight into the diversity of projects worldwide, from innovative single-family houses combining Passive House with low carbon materials, to various more complex non-residential buildings typologies, as new-builds and retrofits. It can also be a great place to look if you are looking for Passive House projects and professionals in your area.
The standard has definitely picked up outside of Europe. There is substantial uptake, for example, in North America, with Vancouver being a prime example of incentivising Passive House through local policy. The next few years are going to be very exciting, as we expect completion of a number of local large scale schemes that could be game-changing for the perception and awareness level of the standard. On the other side of the globe we are seeing continued growth in China – not only in terms of built projects but also in terms of high-performance components, which is absolutely crucial in achieving market transformation. Passive House components can be browsed and filtered by type and country in our component database. Last year also marked the completion of the first regional larger scale non-residential project on the Australian continent.
Also very encouraging to see are Passive House “firsts” in new regions, for example a retrofitted factory in Sri Lanka, new builds in the UAE and in Saudi Arabia, as well as in Brazil. We are also involved in initiatives in India and, as research institute, are taking part in important discussions surrounding the projected rising cooling demand in emerging economies. So, as you see, Passive House is truly expanding across the globe.
2. In 2015, along with the release of the 9th version of the Passive House Planning Package (PHPP 9), the Primary Energy Renewables (PER) method was introduced as well as the Plus and Premium certification categories on top of the Classic one.
May you summarise the rationale for developing this PER approach?
The reason for developing the PER approach is the ongoing transition to an energy supply based primarily on renewable energy. The currently prevalent evaluation systems to measure the overall impact of buildings are non-renewable primary energy (PE), or CO2 as indicator for GHG emissions. These methodologies were developed for the traditional fossil-fuel heavy energy supply structure and they simply don’t do justice to the changing infrastructure with increased renewable energy supply (RES) because they fail to measure and incentivise efficient use of renewable energy resources. Renewable energy generation, transmission and storage requires infrastructure, investments and requires space, which eventually becomes a decisive limiting factor. A sustainable energy supply based on RES can only be achieved if we use these resources wisely and efficiently.
Driven by the urgency of meeting global climate goals, we at PHI developed a new scheme to better reflect synergies between energy efficiency and the use of renewable energy resources. In a nutshell, the PER (Primary Energy Renewable) methodology provides an assessment of a building’s compatibility with renewable energy supply. For example, using a heat pump water heater to produce hot water will result in a lower PER demand than using a gas tank water heater.
In more detail: Renewable primary energy (PER) is the unit of energy generated from renewable resources, e.g. electricity produced by a photovoltaic system/wind turbine. PER-factors reflect the primary renewable resources needed to cover the final energy demand of a building, specifically including distribution and storage losses. The higher the PER-factor, the higher the required renewable energy resources. These PER-factors have been derived based on a future scenario of a 100% renewable energy supply. They take into account site-specific hourly load profiles of the energy demand for different end uses compared to the hourly available renewable energy supply. The heating demand for domestic hot water and for household electricity feature fairly constant demand profiles over the course of the year, and the demand can be covered to a large extent directly from the renewable primary energy source, without the need for storage or via efficient short-term storage technologies. The energy demand for heating, on the contrary, only occurs during winter with lower renewable energy resources. A relevant part of the energy demand must, therefore, undergo seasonal storage, which implies high losses and a higher PER weighting factor. The higher factor provides a direct design incentive to prioritise efficiency measures for reducing the heating demand over measures for reducing cooling demand, which is much more compatible with renewable energy resources.
In addition to differentiating for various end uses of electricity, the PER scheme also considers other fuels in the context of a sustainable renewable energy supply. For example, gas for heating furnaces is considered as power-to-gas, with the respective conversion losses. Efficient use of the highly valuable resource biomass is taken into account via a limited biomass budget.
The aims of the PER methodology are to incentivise electrification (preferably with a heat pump), to limit the use of biomass and to prioritise efficiency measures for those end uses that are least compatible with the regional renewable energy supply. I encourage to dig deeper into the topic by following the links provided at the end.
The additional categories Plus and Premium, on top of Passive House Classic, were introduced at the same time as the PER methodology in order to encourage designers and clients to go the extra mile by adding renewables to their Passive House building. If we want to meet climate goals, we ultimately need both – efficiency plus more renewable energy supply.
This PER indicator of energy consumption is now recommended for Passive House certification over the non-renewable Primary Energy one, which was used before and is still the common reference in standard EPB calculations.
Can you still choose, when certifying a project, to go with conventional PE calculation?
Yes, Passive House certification is possible either through the PER or the PE scheme for the “Classic” category. As soon as renewable energy production is accounted for as part of the project (Passive House Plus or Premium) the PER scheme has to be used.
Do the PHPP calculations still provide both the PER and PE figures in order to maintain a level of comparability?
Yes, most certainly, and that will not change. PHPP provides the calculated energy demand as final energy, as PE, as PER and also as GHG (CO2) emissions. They cannot be directly compared because they have different purposes, but they all have their validity. As described above, PER provides a future-oriented assessment in the context of a sustainable renewable energy supply. PE and CO2 are indicators of the building’s environmental impact in today’s energy supply structure.
Personally, I’d like to encourage all designers to use PER to guide major design decisions, as this will facilitate and the energy transition towards RES and provide long-term sustainable solutions. The structure of energy supply will change substantially during the lifetime of a building that is constructed today, and this needs to be taken into consideration. CO2 (or PE) should be used as a secondary indicator to cross-check the current environmental impact of their choices.
How has the market uptake of the PER indicator been so far… In Germany? Elsewhere?
The Passive House Classes Plus and Premium are certainly popular and we are seeing increased certifications in these categories. As for PE versus PER, we continue to see both being used for certification. Many designers committed to sustainability are promoting PER because they understand and support the push toward electrification of buildings and the importance of moving away from fossil fuels to heat our buildings.
How are the local PER factors defined (by city or by country) and how often are they updated?
The PER factors are provided as part of the PHPP climate data set and are therefore defined for each location. Since the PER scheme is based on the future goal of a 100% renewable energy supply there is no need for periodic updates to keep up with the development status of the energy transition. Having said that, the future scenario is, of course, based on some assumptions made to the best of our knowledge and latest research, e.g. using Power-to-Gas as the main seasonal storage technology. Some of these assumptions may change and we will update the PER methodology/algorithms if this should be the case.
3. According to the EPBD directive, starting from 2021 all new buildings in EU Member States should be nearly zero-energy buildings (NZEB)
Although following different national definitions and calculations, such buildings are meant to be energy-efficient and cover a ‘very significant’ part of the near-zero energy needs with renewable energy sources (RES). When speaking of “Net-Zero” or “Plus-Energy” buildings, the level of coverage of the energy needs by RES should be complete or exceeding those needs.
Can this approach compare to the PH Plus and PH Premium certifications levels?
Qualitatively, the approaches of “Net-Zero”/”Plus-Energy” and of Passive House Plus/Premium all aim to promote both energy efficiency and renewable energy supply. When looking at the approaches in more detail, however, they do not directly compare.
In the “Net-Zero” approach, the energy demand is offset by the amount of RES generated over the course of the year. It is intuitive and easy to understand but it ignores the effects of renewable energy storage and associated losses, as described earlier. Furthermore, it penalises multi-storey buildings, because more storeys lead to a higher overall energy demand, which in turn will require more RES for net-zero offsetting to be generated on a similar sized roof space. This is a misleading design incentive, as bungalows are certainly unfavorable in terms of land use and resource requirements.
By using the PER demand as indicator, Passive House inherently includes an allowance for losses for renewable energy storage. And instead of offsetting, the Passive House categories Plus and Premium are based on an independent rating for energy efficiency and for renewable energy generation. The level of the building’s energy efficiency is rated based on the conditioned spaces (energy demand per m² living area), whilst the level of renewables is rated based on the area occupied by the building (energy production per m² projected footprint). If renewable electricity is generated on this area, this creates an additional benefit. After all, the sun shines on the roof and not on the useable area in the stacked storeys. That way, a multi-family building with a roof largely covered with PV can achieve a Plus or Premium rating as easily as a single family bungalow.
Comparisons can be useful for more context: For a single family house, a Passive House Plus will roughly equate to a Net-Zero building, whilst a Passive House Premium will likely be a generous Plus-Energy building.
How far an NZEB building (let us say in German regulation) can be from the efficiency levels of the PH requirements?
For Germany, from experience, the heating demand for a Passive House (15 kWh/(m²a) per definition) is around 60-75% lower than for a building compliant with the current building code GEG 2020. There is definitely still a lot of untapped savings potential.
As you mentioned before, nZEB is defined very differently by each member state. There is no universal definition and because of the very different interpretations of the EPBD directive, it is not only challenging to compare the nZEB efficiency requirement of different member states, but also to compare nZEB efficiency levels with Passive House. Passive House differs from nZEB in that it has very clearly defined absolute energy demand requirements, whereas nZEB often uses relative savings compared to a reference building as the compliance metric.
Passive House does tick all the nZEB boxes. Nearly-zero energy demand, being cost-optimal from a lifecycle perspective and receiving significant contributions from RES (for PH Plus and Premium, and for PH Classic with a heat pump). So, a Passive House is most certainly an nZEB, but nZEB typically does not exploit the efficiency levels of Passive House. It would be absolutely fantastic to gain official recognition by individual member states, or even by the EU, for Passive House as one possible compliance pathway for nZEB.
Is there a PER factor somewhat considered in EPB or other certifications?
PER is specific to PH and is so far not considered by any other standards. There seems to be increasing awareness about the limits of PE as indicator in the context of increasing renewable energy supply and a search for alternatives. As far as I am aware, no other standard has adopted new rating schemes. My hope is that PER is recognised by policymakers as a contribution to the discussion and potential way forward. It is important for policy to move forward from the current PE rating scheme, which is becoming outdated and inapplicable as the share of RES in the energy mix increases.
4. Finally, in PHI you have studied the impact of future climate scenarios on the performance and comfort of buildings. What are some key insights from these researches?
Yes, we are looking at the impact of future climate scenarios on building design choices and buildings’ energy performance – and we are not the only ones. I presented part of our most recent work on the topic at last year’s online International Passive House Conference, where we looked at the energy performance impact when modelling selected existing Passive House projects under future climate scenarios in PHPP. We looked at projects in Germany as an example for heating-dominated climate conditions, at projects in Greece and New York as example locations for climates that call for both heating and cooling, and lastly, we looked at Delhi as a location which is entirely cooling-dominated.
Unsurprisingly, there is a general trend for decreasing heating and increasing cooling needs. Overall, the results indicate that the primary design decisions remain unchanged. Building according to the Passive House concept provides resilience for harsher climate conditions, especially with regard to projected cooling peaks.
What is the time scope of these scenarios?
In the study I presented, we looked at future climate scenarios for 2050 (in 30 years’ time) and 2100 (in 70 years’ time) using climate data projections created with the climate software Meteonorm. The lifecycle of buildings is fairly long and they will most certainly be exposed to climate conditions of the late 2000s – or even longer. Climate scientists are doing an incredible job at modelling future climate scenarios but, as with any projection, we don’t know how things are going to pan out. As part of the study, we looked at both low and high climate change projections. The results are fairly similar for both scenarios in the case of the mid-century projection but vary significantly by 2100.
Can future summer comfort in PH (or not PH) buildings be jeopardised if measures or provisions are not already taken today?
In some cases, yes. If a project already has active cooling then, no, future summer comfort is not jeopardised. The cooling demand is projected to increase but in the case of a Passive House, the increase will only be small and in most cases, the cooling system dimensioned for today’s climate will suffice.
The buildings that are potentially at risk, are those that don’t have active cooling in locations where summers are currently just about comfortably warm but are projected to get hotter, for example in Central and Western Europe. Especially buildings with dense occupancy in urban settings (where it is often warmer due to the urban heat island effect) need to be looked at carefully. In such cases, we most certainly need increased focus on summer comfort and passive cooling design strategies. We can learn a lot from building traditions that are already common in the warmer areas, for example in Southern Europe. It is important that we embrace and integrate passive cooling measures into current designs more, especially with regard to solar gains (orientation, glazing ratio and effective, reliable shading, shading, shading), as well as effective summer ventilation strategies e.g. cross-ventilation at night. And this holds true for Passive House projects, as well as for less energy-efficient buildings, new and old – all buildings are affected by the warming trends.
Depending on the project it can absolutely make sense - or even be necessary - to anticipate some active cooling in order to be able to provide healthy and comfortable indoor living/working conditions also in the future. What we certainly need to prevent, is for a building being built today, to be retrofitted with inefficient individual A/C units in a few decades time. Here also, energy efficiency is key.
For any building without active cooling, I strongly recommend a careful analysis of the summer comfort, also taking into account warming climate conditions. Since it can be difficult to obtain data for climate projections, we’ve released a tool for a simplified approach of modifying summer temperatures of PHPP climate data. The tool can be downloaded on the Passive House Institute’s website here (under “summer temperature tool”). Monitoring data and experience clearly shows that the way a user interacts with the building also has an immense impact on summer comfort, often more so than warming climate conditions. In order to raise more awareness of the subject, we are integrating a “summer stress-test” into the next PHPP release, version 10. With this stress-test, we intend to encourage design choices that are more robust with regard to ensuring summer comfort, today and in the future.
When building in 30 years’ time would less insulation be required to reach PH standard?
What our study clearly showed, is that insulating to Passive House levels under current climate conditions is not counterproductive in any way. Especially in climates with active cooling, where a significant increase is being predicted for the energy demand, Passive House insulation levels play a crucial role in reducing the cooling needs.
The concept of Passive House is about much more than higher insulation levels. The standard is about improving the design and selecting appropriate components for high comfort and low energy demand. Designing to Passive House under today’s climate conditions provides resilience for future harsher climate conditions.
Links for further reading relevant to the interview
General Passive House Links