session title SESSION XI

Optimising Passive House: A look at Kranichstein (and Saskatoon) through the lens of PDT-Passivhaus

Bronwyn Barry, ProtoLife & One Sky Homes 2875 21st Street, San Francisco, CA, USA Bronwynbarry67@gmail.com

1 Introduction

Until recently, no optimisation tools were readily available to Passive House Planning Package (PHPP) users except for those willing to program macros within the Excel spreadsheet or explore manual iterations by hand. This paper explores the building energy optimization process of the Kranichstein Passive House and another cold climate project using ‘PDT-Passivhaus’.

‘PDT-Passivhaus’ is a new software as service (SAS) tool that was developed to assist designers and architects with finding the most efficient combination of building components. This service offers an alternate to the new ‘Variants’ calculations available in PHPP 9. It provides two paths for optimisation:

1. Multi-variable optimisation allows the designer a parametric study of isolated components to view the effect of their manipulation on the four basic certification metrics (Heating Demand, Heat Load, Cooling Demand and Primary Energy). These variables are looked at in isolation. All other variables remain constant.

2. Full Optimisation allows the designer to explore the optimised combination of a range of variables reviewed in combination with each other. The designer may select to review a range of best possible combination of certification results between the top 5 and the top 100. An accompanying data table may be downloaded to compliment the graphic output.

PDT-Passivhaus is distinct from the PHPP Variants offering in that it delivers graphic outputs that do not directly modify the client’s PHPP file. This allows users to safely explore thousands of variables either singly, or in combination, without making unwanted changes to their PHPP file.

2 A Look at Kranichstein Using PDT-Passivhaus

Running the Darmstadt-Kranichstein PHPP through PDT-Passivhaus yielded illuminating results (Figures 1 to 4). When selecting the following variables in isolation – total window surface area; average window U-value; exterior walls U-value; partition wall U-value; airtightness benefit; north window area; south window area and west window area – it was found that every single one of these isolated variables was apparently designed and built to

SESSION XI session title

the 10 W/m2 heat load criterion currently defined by the Passive House Standard. Values of each of these variables fell below the 15 kWh/(m2a) heating demand criterion, indicating this metric was not the primary focus of the Kranichstein project team. Notably, the 15 kWh/(m2a) heat demand value was only within close range of the outputs for exterior walls, HRV efficiency, total window surface area and average window U-value.

Figure 1: Exterior Wall U-Value Figure 2: Basement Ceiling U-Value

Figure 3: Roof U-Value Figure 4: Window Surface Area

2.1 Kranichstein South Windows

In exploring the South Window Area as a single variable (Figure 5), it was interesting to note that halving the total south window area would have decreased the Heating Demand

session title SESSION XI

of this building. However, it is clear that due to the minimal reduction in Heating Demand, designing Kranichstein to the Heat Load criteria was clearly the better choice.

2.2 Kranichstein Future Window Replacement

Because Kranichstein is already a realised building, the value for running multiple variable optimisations for typical assemblies and components was not so interesting. Results showed both the Heat Load and Heating Demand could be further reduced, which is logical (Figure 6). However, there is no indication that further reductions would be either valuable or more economical.

A more interesting exploration for the Kranichstein project was to look at the options for future window replacement, given that windows could be more readily and likely exchanged after some 30–40 years of service. Performance values of this particular component have also drastically improved over the past 25 years since Kranichstein was built.

The window glass U-value of 0.35 W/(m2K) for replacement windows was shown to yield the highest number of values that would result in a reduction of the heating load. Various combinations of spacer Psi-values and window frame U-values were all shown to deliver successful results within the range of values specified for this particular optimisation.

Figure 5: South Window Area

Figure 6: Full Optimisation for Window Replacement, Top 20 Results

●

●

●

●

●

●

●●

●

●●

●

●

●●

●

●

●

●●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●●

●

●

●

●●

●

●●●

●

●●●●●

●●●●

●●●

●●●

●●

●●

●●

●

●

●

●

0.504

0.788

0.036

0.074

0.35

0.525

9.206

9.343

Win

dow

Fra

me

U−V

alue

Win

dow

Spa

cer P

si V

alue

Win

dow

Gla

ss U−V

alue

Spe

cific

Hea

ting

Load

variable

valu

e

Full optimization, top 1 − 20 results

SESSION XI session title

3 Saskatchewan Demonstration Project

Projects in the design and schematic phase present greater opportunities for optimisation. For this reason, a theoretical project was developed in order to demonstrate the usefulness of PDT-Passivhaus as an optimisation tool.

The project chosen was a single family detached house located in Saskatoon, Saskatchewan. This climate region is classified ‘Arctic’ by the Passive House Institute (Figure 7). Initial PHPP inputs showed the building did not meet certification criteria (Figure 8).

Figure 7: Climate Data Information taken from PHPP 8.4 for Saskatoon, Saskatchewan, Canada

Figure 8: Initial PHPP Verification (Before)

Using the information provided by the energy balance graph on the PHPP Annual Heating Sheet, a PDT-Passivhaus Full Optimisation, selecting window area, ventilation losses and exterior wall to ambient values, was calculated (Figure 9).

Results showed two constants:

• Window Area of 12 m2

session title SESSION XI

• Airtightness Benefit of 0.18 h–1

All combinations of the selected variables resulted in a specific space heating demand of 25.022 kWh/(m2a). This was a reduction from the initial value of 44 kWh/(m2a) – a 57 % improvement. Other component results indicated that the building assemblies for this particular project would not need to be as highly insulated as initially assumed.

A comparison of ‘before’ and ‘after’ assemblies and components (Table 1) showed that when the window area was reduced to 16.46 m2, an airtightness benefit of 0.2 h–1 was met, and the average window U-value was improved to 0.62 W/(m2K), then U-values for the roof, walls and slab could be increased and required slightly less insulation. (Note: it was not con-firmed that these higher U-values would still meet the comfort criteria for this location.)

Once these recommended values were input into the sample PHPP, it was shown that this building could comply with the Passive House Standard certification metrics and would achieve certification via the 10 W/m2 heat load criterion (Figure 10). The specific space heating demand remained above the 15 kWh/(m2a) limit and was finalised at 27 kWh/(m2a).

Table 1: ‘Before’ and ‘After’ Comparison Values for the Primary Building Assemblies

4 Conclusions

Using PDT-Passivhaus to both explore the Kranichstein Passive House and the theoretical project located in Saskatoon, Saskatchewan, proved extremely useful. It revealed specific

Figure 9: PDT-Passivhaus Full Optimisation for the Saskatoon, Saskatchewan, Building

SESSION XI session title

information regarding certification via Heat Load vs Specific Space Heating Demand. Kranichstein was very clearly and deliberately designed to target a Heat Load of 10 W/m2. This makes good sense, given that the historic basis for the Passive House standard evolved out of the goal of delivering heating and cooling via the ventilation system. Using PDT-Passivhaus made this exploration very simple and clear through the graphic outputs provided by the service.

Figure 10: Revised PHPP Verification (After)

Exploration of the additional project located in a more challenging, Arctic climate, showed that certification via the Heat Load alternate path was the optimum choice for this project. Indeed, it appears that projects in this location would be hard pressed to use the Space Heating Demand path.

Both projects demonstrated that designing to the Heat Load requirement was the optimum solution. The Heat Load criterion was shown to be flexible and achievable for buildings in two very different climates. Given this information, it is curious that the 15 kWh/(m2a) target metric has become most commonly associated with the Passive House standard. Removing the 15 kWh/(m2a) certification path may offer a further simplification of future versions of the Passive House standard and help clarify the inherent flexibility and climate independent nature of designing buildings to meet the Heating Load metric of 10 W/m2.

Ultimately this exploration revealed both obvious and tangential benefits of the optimisation process. PHPP users should all be encouraged to integrate an optimisation process into their design process.

5 References

Heating Load in Passive Houses: http://www.passipedia.org/basics/building_physics_-_basics/heating_load

http://passivhaus.protolife.com/

session title SESSION XI

Summary

‘PDT-Passivhaus’ is a new software tool that was developed to assist designers and architects with finding the most efficient combination of all their various building components. This paper explores the Kranichstein Passive House building and another cold climate project using ‘PDT-Passivhaus’.