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State House to Passive House 7 – Step 3 – The Joy of Modelling

When I was at architecture school, (a few years ago), I remember going on a tour of a recently completed building with the architect. It had a communal area that had glazed walls and roof to the north. The architect sheepishly said there were (massive) overheating issues and they may have got it wrong. Heat loss would have also been a problem.

I also remember using a simple building modelling tool called ALF to learn the effect of window area percentages on different elevations. Architectural design is often instinctive, but we can’t afford to leave a building's performance to instinct, at a time when we need better performing buildings, with emissions that are near zero. More than ever, we can’t leave things to chance.

designPH model with the Eastern Hutt Hills or dawn wall in the background

Modelling should be part of an architect’s design process. It’s a great teacher. It’s a great way to test ideas, find better ideas, and refine a design. Modelling with designPH and PHPP are the best ways I have found to do this, through a comprehensive system that makes sense. The Passive House Standards provide the goals that combine a sweet spot of comfort, health, durability, energy efficiency, and value.

Street elevation with the large Pūriri street tree and potential additional dwelling. The treated floor area plan in yellow beyond.

Having got my concept design, it was now time to find out if it was any good. How could make it be better. designPH works through SketchUp as a plug in where you can quickly build the geometry of the building, put it in its exact location/climate, with features that provide shading such as hills and trees.

You can put in the fabric build up, working out element’s insulation levels. You can provide precise details about the windows performance and placement. Reveal depth can make such a difference. You can put in different building shading elements, test the results, record it, make a change, and quickly rerun it. In my model, I put in a potential future building on the site.

Tracking results and options in designPH. It would be good if I wrote down what they all were!

The results in designPH won’t be as accurate as when you export the data into PHPP but it can get you into the ballpark. They are usually higher leaving room for improvement. With these results you can have an initial consultation with the certifier, getting feedback on more improvements.

Initial results once the data is exported to PHPP. Its promising but can I do better.

So, what did modelling this house teach me?

1. I had previously looked at EnerPHit for a single story detached house. I could not get that project to work by the modelling method and had to use the more onerous expensive component method. Here with a more compact semi-detached form factor, not only did the model work, but the full Passive House Standard was also possibly within reach, with 100mm walls, rather than just the less onerous EnerPHit Standard. Form Factor is King!

2. This is also a testament to the carefully considered windows of the State House design. The windows are well optimised. It has good daylight inside, but the window area isn’t too high. EnerPHit was possible with just double glazing!

3. I thought I needed a veranda on the sunny northwest rear elevation over the large sliding doors to avoid overheating, but it was not the case. In fact, I lost too much solar gain. Kara was right about eaves, it’s a two-edged sword and something that can be altered with the conditions is better. I’ll allow power for a retractable awning to provide shading when needed and to give covered outdoor space.

Now with these results, I can go shopping!


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