Paper delivered and published in the proceedings for the 2016 International Passive House Conference, Darmstadt, Germany. This paper accompanied the slide presentation of the same title and looks at the optimization of the Kranichstein Passive House and another house in Saskatoon, Canada.

1. 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

2. 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/(m2
a) heating demand criterion, indicating
this metric was not the primary focus of the Kranichstein project team. Notably, the
15 kWh/(m2
a) 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

3. 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/(m2
K) 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
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0.504
0.788
0.036
0.074
0.35
0.525
9.206
9.343
WindowFrameU−Value
WindowSpacerPsiValue
WindowGlassU−Value
SpecificHeatingLoad
variable
value
Full optimization, top 1 − 20 results

4. 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

5. 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/(m2
a). This was a reduction from the initial value of 44 kWh/(m2
a) – 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/(m2
K), 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/(m2
a) limit and was finalised at 27 kWh/(m2
a).
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

6. 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/(m2
a) target
metric has become most commonly associated with the Passive House standard.
Removing the 15 kWh/(m2
a) 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/

7. 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’.