Thursday, April 29, 2010

Airtightness revealed

Here comes a short explanation how we went about planning construction for the small passive house. First, I created a box without windows with the expected floor area, optimized it for maximum use of existing board materials without need for cutting and calculated PHPP without any windows. I then added windows to optimize the gains. And experimented with airtightness and ventilation systems...

Obviously, sealing the envelope (as I mentioned before in my blog) played an important role. We have achieved n50=0,17 1/h before, so our target to get below 0,3 every time we build should be realistic. A visible airtight surface during construction should enable that.

This surface could not be on the outside. The building should be possible to build any time of the year, and tape doesn't stick well at low temperatures. So it had to be on the inside of insulated, ready-made elements.

The airtightness layer should never be completely inside, there should always be space for installation in front of it. No penetration of the layer should be necessary except for a few.

So what we ended up with is an insulated envelop, with panels going over two stories, capped of by roof elements. With elements made with TJI's and an airtightness layer from OSB, it should be strong enough to hold up a few days by itself. We will tape this empty box from the inside and achieve airtightness straight away (windows are preassembled).

The next days we build the inner load bearing structure as a stud wall, assemble the floor and the load bearing dividing wall. All inside a cosy and warm (airtight) shell. This stud wall will also function as an installation layer for cables/tubes and as support for dry wall.

We can't wait testing it out in practice, going to be a major revolution if it works out the way we expect.

Saturday, April 17, 2010

Cradle to cradle

Passive houses are about energy efficiency and comfort. But as a juror in the re:design award I again became aware of how important it is to take a closer look at material life cycles.

Solving the problem by reusing our trash is not the way forward - it does not give us less trash, but just extends the life cycle of the material.

Energy efficiency and curbing CO2 emissions is todays trend. With so much free energy (there is 40000 times more solar energy hitting the earth than we need, we just have to figure out how to reap it's benefits more efficiently) the future will be how to deal with what is really scarce on this planet - materials - and how to avoid pollution in the confined space we live in.

One way forward is to put limits on consumption and tell everybody that we should be satisfied with less. If anybody believes restricting themselves voluntarily is the true nature of human kind, think again. It will never happen.

We always want more. Passive houses are a good example how energy efficiency (less consumption) can be achieved by more comfort and a better living experience. People want passive houses because it gives them more - with the benefit of using less. That is why the passive house movement is so exceptionally successful, even with slow or no government support.

The only reasonable approach to long term sustainability I have found is the Cradle to Cradle approach. Compared to energy conservation a less known, but similarly important concept. A simple concept but with very complex implementation - probably the reason for not making the news headlines today. But I am in no doubt, that when the have solved the efficiency and green energy problems of today, this is going to be the next Big Thing.

As a student I created a design of a dustpan and brush called "JAMES", that to a large degree fulfills the Cradle to Cradle concept, although at that time I did not know. It just felt the right thing to do. The Dustpan is made of one piece of highly recyclable aluminum (long before any unibody design from Apple :-)) and the brush is made purely from natural materials. The aluminum can be recycled without the loss of quality in a technical cycle and the brush can be given to rot and nurtures new life.

Targeted for ALESSI, the design unfortunately never made it into production, but they added it to their ALESSI Museum. Well, for a student that was success enough.

Tuesday, April 13, 2010

How about a small passive house?

This is my first blog and I will continue to add some insights that will hopefully be valuable to other architects and builders of passive houses.

First about a new project we are working on - a very small passive house to be built repeatedly (mass production would be a too optimistic term :-)

Building costs are usually estimated by floor space or building volume. A smaller house should be cheaper than a bigger house. But many costs do not grow linear, so half as big does unfortunately not mean half the price.

Costs are not only influenced by size, but for example design, efficiency of construction, technical installations and much more.

Our solution has been to completely rethink how to construct and assemble the house. We had two main goals, first: build quickly and anytime of the year, and two: achieve standard airtightness of n50 < 0,3 1/h.

This is where size meets passive house: without a very good airtightness, it is much harder to achieve the passive house standard (anybody using PHPP knows that this is valid for bigger buildings as well). For this small PH, going from 0,2 to 0,6 means a hike of the annual heat demand from 14,9 kWh/m2 to 18,1 kWh/m2, monthly method.

The air flow volume for a small house is also critical: A sufficient air exchange of 74m3/h corresponds to an exchange rate of 0,34 1/h, a higher rate can easily lead to dry air in winter time. So choosing a system that can provide high efficiency at low volumes has been critical.

Our first thought to install a compact unit failed just on this point: the smallest unit on the market still needs an air exchange rate of 105 m3/h to be able to extract enough heat. Not only does the compact unit have a lower heat recovery efficiency, but increasing the ventilation to 105 m3/h would lead to an air exchange rate of 0,47 1/h and combined increase the annual heat demand by 2,4 kWh/m2/a.

(All calculations are based on climate conditions in Žilina, the most difficult to achieve conditions in Slovakia)

More on other topics next time... maybe you've  figured out our buiding system by then :-)