Authored by: Elena Reyes Bernal, Zeno Bastian, Jessica Grove-Smith, Jürgen Schnieders

For building certification according to the Passive House Standard there are fixed renewable primary energy demand criteria: 60 kWh/(m²a) for Classic, 45 kWh/(m²a) for Plus and 30 kWh/(m²a) for Premium. But the certification criteria [PHI 2016] also states the possibility for exemptions in case of special uses with high energy intensity. Project teams can request a project-specific target, which is defined on a case-by-case basis.

The number of larger and mixed-use Passive House buildings has significantly increased in recent years, with more and more projects applying to the Passive House Institute for primary energy exemptions. In order to provide more transparency, more consistency and to streamline and accelerate the certification process for these buildings, Passive House Institute is developing a scheme for a standardised approach to apply for project-specific primary energy requirements. This will also provide developers planning security from the early project stages on, thus making Passive House a more tangible target to aim for.

In a first step this scheme has been developed for densely occupied residential buildings, and implemented in a tool that sets a primary energy target based on the end uses in the building. This project was carried out by Passive House Institute in cooperation with and with support from the Vancouver Zero Emissions Building Exchange (ZEBx) and a technical committee of Passive House practitioners from across North America. This paper outlines how the scheme was derived, as well as the implications for certification of applicable projects.

One of the main factors leading to an exemption on the PE/PER criterion in residential projects is density. Smaller dwelling units typically have a higher specific energy consumption per m² living area. This is caused by (a) a typically higher number of people per m² of living area [PHI 2015a] and (b) a similar number of appliances (fridge, washing facilities, electronics, etc.) if compared to a larger dwelling unit but in a smaller living space. Multi-family buildings also have additional energy uses compared to single-family homes: additional equipment such as pumps and elevators, and additional areas such as corridors, amenities and storage rooms (in this paper collectively referred to as “common areas”).

The first step was to identify the most relevant energy uses in residential buildings. Then, appropriate efficiency targets for each end-use were derived based on the Passive House criteria, recommended values for Passive Houses, standard values and auxiliary calculations already integrated in PHPP, and efficiency values of available technologies in the market. These values give a target for final energy which then is translated via conversion factors into Primary Energy (PE) or Primary Energy Renewable (PER) targets. The conversion factors used for the respective scheme take into account the energy carrier, end-use and location. The calculated targets were then verified by comparing them to the PHPP models of projects that have been certified or are currently under certification.

Table 1: Targets per end-use and conversion factors to PE/PER demand. © PHI

The appropriate efficiency targets for each end use were defined as follows:

• Heating, cooling and dehumidification: The Passive House criteria for these end-uses form the basis for the targets.

• Ventilation, domestic hot water and household appliances: these targets are set in terms of energy demand per person, thus scaled with density.

• Auxiliary electricity, common areas, and elevators: these targets are adjusted based on project characteristics - size (TFA), number of dwelling units or whether the project includes elevators and/or common areas.

Table 1 includes the targets and conversion factors for each end-use. During the transition to a complete renewable energy supply PER, Passive House certification is available either through PER or PE demand. The adjusted target is therefore also available for both schemes.

The applicability of the new approach for defining project specific PE/PER targets was verified in detail through 6 projects in different climate zones: 5 multi-family projects and one single-family project (the default example in PHPP). The analysis included a series of scenarios reflecting the performance of the building with different levels of efficiency for the equipment and devices. Table 2 summarizes the main characteristics of the different scenarios and Figure 1 includes the main results of the analysis.

Table 2: Characteristics of the different scenarios used for the verification of the PER/PE target. © PHI

As Table 2 shows, the scenarios involved changing equipment and devices but did not explore the improvement of other aspects affecting the energy balance. The analysis indicated that the generic 60 kWh/(m²a) PER criteria may not be achieved in projects with smaller dwelling units without compensation through renewable energy generation. Except for the single-family home (far right in Figure 1), the projects were all above the threshold unless the best devices available were used. For those cases with the smallest dwelling units (towards the left in Figure 1), a combination of the best devices and efficient heat pumps was needed.

Figure 1: PER demand achieved with devices and equipment available in the market (bars) vs. the calculated PER target with different factors (lines). © PHI

The results clearly indicate that the target increases with density: the smaller the dwelling unit, the higher the new PER threshold. The adjusted PER target, however, is above the original threshold, but still below the scenario “PH suitable devices”. This suggests that some aspects of the original projects (e.g.: distribution losses in the DHW system) may still need to be improved or the project would need equipment or devices which perform better than the average Passive House to qualify for an exemption.

A second analysis was carried out to verify the calculation for additional project characteristics and locations. An additional set of 28 residential projects was calculated, including different sizes and number of dwelling units, in all Passive House climate zones (except arctic). Figure 2 includes the results of the second analysis.

Figure 2: PER and PE demand modelled for each project (bars) compared to the original PE and PER criteria (continuous lines) and the adjusted targets (dotted lines with markers). © PHI

The analysis confirmed the following:

• The adjusted target is feasible when compared to existing PHPP models. All but one of the projects (see Figure 2) are certifiable either through the adjusted PER or the adjusted PE scheme. The main factors affecting the performance of the project that is not certifiable are a very inefficient elevator, and the direct electric heating. By changing any of these two, the project would be under the PER threshold.

• The exemption is only granted if energy is used efficiently for all significant devices. It does not represent a “relaxation” of the original criteria. As soon as the dwelling size is large enough (approx. 75 m² for PE and 90 m² for PER) the calculated target is close to or below the original criterion.

• The projects that surpass the adjusted limit for PER feature a boiler for DHW and/or heating. This appropriately reflects the fact that such fossil fuel based solutions are not recommended in a sustainable renewable energy supply. Such projects are currently certifiable through PE, as long as the transition phase to PER is still in place.

• There is only one project where the PER demand is higher than the PE demand (see Figure 2). This example shows the main difference between the concepts of PER and PE: the PER scheme assumes a complete transition to renewable energy supply and thus reflects the projects’ renewable source energy demand [PHI 2015b], whilst PE reflects the fossil fuel based source energy in the current/past energy supply structure. In this project, pellets were used as a heat source for DHW and space heating, resulting in a low PE demand but a high PER demand, as the use of biomass is no longer sustainable (a higher conversion factor is used) once the budget is exceeded.

• In Passive House projects where the energy for heating and cooling has already been significantly reduced, the contribution from other end-uses to the total energy demand becomes more relevant. The analysis showed that there is a great potential for further reducing the energy demand (a) from domestic hot water, by limiting distribution losses; and (b) from household appliances, by using more efficient devices readily available in both the European and North American markets.

For projects applying for an exemption to the generic PE/PER criteria, the target can be calculated using the newly developed tool that is linked to the project’s PHPP file. The tool also allows to compare the target per end-use to the project results (see Figure 3), making it easier to identify the end-uses where the energy demand can be improved.

Figure 3: Sample of the results obtained with the tool comparing the targets for final, PER and PE demand to the project results. © PHI

The calculation is currently only valid for residential buildings. If the building includes other uses (e.g. retail, swimming pools), the total limit will be the combined target for the different uses (area-weighted average). The adjusted PE/PER target will be implemented in a test phase, during which the tool will be made available through accredited Passive House building certifiers. After the test period, the calculation will then be integrated in a later version of PHPP.

The target for PER demand can also be adapted for its use with the classes. The criterion for generation of renewable energy does not change, but the PER demand becomes the target as calculated for Passive House Classic, the target -15 kWh/(m²a) for Passive House Plus and -30 kWh/(m²a) for Passive House Premium. As Figure 4 shows, the alternative criteria that allows an increased energy demand through compensation with renewable energy generation, is also adapted accordingly.

Figure 4: adjusted PER demand and the classes. © PHI

Up to date, the Passive House criteria included a fixed primary energy target that needed to be met. Exemptions were available for individual cases upon careful assessment by the Passive House Institute of the implemented efficiency levels. The newly introduced methodology to calculate PE/PER targets, based on the end-uses available in a project, allows for a much easier, faster and transparent definition of the permissible PER demand if an exemption to the criterion is needed. This provides more certainty from earlier stages of the planning process and, by recognizing the effect of density and additional energy uses, the new methodology will notably have positive consequences for densely occupied multifamily projects that previously struggled to meet the PER criterion. It properly recognizes outstanding projects where additional efforts to improve energy efficiency beyond the Passive House targets are combined with generation of energy through renewable sources.

In the longer run, it is envisaged to extend the newly developed tool and methodology with the goal of establishing clearly defined PER targets for a wide variety of building typologies with high energy intensity.

This paper outlines the methodology to derive PE/PER targets for residential projects with high density. These are calculated with a tool that is linked to a PHPP file, and are based on the sum of primary energy requirements for individual end-uses in the building (e.g.: lighting, elevators, etc.).

This article was developed in the framework of the “Project-specific PER” project. This project was administered by the Zero Emissions Building Exchange with funding from the City of Vancouver, Natural Resources Canada and the BC Ministry of Energy, Mines and Petroleum Resources.

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Renewable primary energy demand in residential buildings with high energy intensity