Category Archives: Ventilation

Reflections After a Year of Living in Our Passive House

Although there is always more to do, at the end of 2017 and after a year of living in our passive house, it’s a good time to reflect on the whole process.

This place was both the product of a shared dream between Kayo and I to create a sustainable and comfortable family house and an experiment for all of those involved. Sitting here on a late December morning after a night when the temperate dropped to an unusually cold -24ºC (yes, and that’s without wind-chill) outside and looking out on the sign shining on half a metre of snow, while feeling totally comfortable inside at 21ºC, we think we’ve achieved our dream and the experiment has been a success! We would even stand by the revised cost estimates we produced back in December 2015.

Wolfe Island Passive House in winter

There are some remaining problems. The first is a building envelope tightness issue that is due to a manufacturing fault. The Optiwin Motura sliding door, which was a prototype, has never sealed as tightly as it should, and last winter and this, we’ve resorted to sealing it up with gasketing and tape to maintain the building envelope. However, this is fixable: Optiwin have been as thorough and responsible as ever, and both issued us with a partial refund for the door and got back to is with a very detailed analysis of the fault and how to remedy it, which we will be putting into place in the spring. I don’t think anyone else considering using Optiwin needs to worry about this – as I said, our door was an early version and the current models are already better.

The second issue was noticed by Malcolm Isaacs, our passive house consultant, in checking the report conducted by Anthony Mach. He reckoned that the passive solar heat gain in winter is not as good as it was in the calculations we made. In other words, the house is not as warm as it could be. It’s not actually something we find uncomfortable, it’s more an optimum performance issue. The reason, we think, is that the downstairs porch roof overhang is not quite the exact height / angle / extension as in the original designs. However this means that to remedy the (small) differences, we’d have to almost completely rebuild the porch. There were at least two points at which things were changed in the design process that could have affected this, and as we were working not only with an architect and builder but also a passive house design consultant and engineer, and a manufacturer (for the pre-fabricated CLT structure), there were even more communication issues to manage than in a normal build. These communication issues can be crucial and really, all calculations need to be checked and recalculated every time there is a change. And of course, when you are working with any kind of pre-fab, there is a point after manufacturing has started that you can’t change anything about that any more and any changes from that point onwards have to be adaptations to what you’ve had manufactured.

Related to the issue of the passive solar heat gain – had we known this was going to be the case, then we probably would have had underfloor heating installed. In fact, we probably should have done anyway as a kind of reserve. Had we done this, we probably wouldn’t have needed the little Thermolec air heating system we have as part of the ventilation. We were just assured that it would be so warm anyway that underfloor heating wouldn’t make any difference. That’s not really true in practice but it’s warm enough so we aren’t complaining! Again, at this point it would mean substantial rebuilding (ripping up and relaying our lovely wooden floors) to do this. The lesson is: lay the underfloor heating even if you end up not using it. It’s better to have the possibility than not.

The other remaining problems are small design issues, that people thinking about building a passive house, or even just any house should note. The first is that although we really like our open-plan downstairs space, and visitors love it, however Kayo would now want a more specific dedicated work area or room. What we did design in was inadequate. It’s difficult to see how we could have done this just by tweaking the design we have. So, it we were starting again, we would include this as one of the essential elements and design around it, as we did with the kitchen.

The second minor element does relate more to passive house design, and it is the way the entrance works. We have an amazing Austrian-manufactured passive-house-certified front door from Tarredo. The only problem is that you still have to open it and once you open it, it doesn’t matter how insulated the door is. Of course, no-one leaves the door open very long in winter in any house but any heat loss is a problem in a passive house in very cold climates. Back when we were still thinking about rebuilding our old house, we had designed what we refered to as an ‘air-lock’ (like in space-ships), which was essentially an insulated porch outside the building shell, which had two insulated doors to outside and inside. Somehow, that element got lost when we moved to designing an entirely new house. I’d really recommend to anyone building a passive house in a cold climate to think about this because, especially around the Holiday season when you have people coming and going, the front door gets opened a lot more than you’d like from a passive house point-of-view! The plus side is that the more parties you have, the more all those people in your house also heat it up substantially. However, whichever way you are thinking about it, you have to factor people and behaviour into your design. The good news is that this particular problem is easily resolved. We think what we will do is create a closed-in porch space outside the front door. We’ve got room. The only question is whether we make it permanent or seasonal and removable.

There is really nothing that has happened in this year of living in our new passive house that has made us regret or rethink the building process or the big decisions we made in the design.

The Zehnder ERV is a minor miracle. The air quality in the house is so good that it almost makes us forget the mould-infested air we used to put up with as normal in practically every other house we’ve ever lived in. It just keeps working in the background with minimal need to maintanance (occasional cleaning or replacement of filters).

We still totally recommend using Cross-Laminated Timber for the structure, however we don’t think it’s necessary to use it for all interior walls, and combining CLT for the main structural walls, with more standard stick-frame and drywall for the other interior walls would make for a more flexible design that would allow you to do things like changing your mind on where electrical sockets etc. go – and even where the walls themselves go.

However, we know that Canadian manufacturers, at least in the East, are still not capable of doing the precise factory-cutting that we had done. Someone needs to make the necessary investment to do so, because CLT should be a standard material in home-building here considering Canada’s timber resources and need to well-insulated homes in a world where we are at the end of the era of limitless oil and gas for heating. Were anyone to use Canadian CLT, however, you wouldn’t be limited, as we were, by the dimensions of shipping containers. You could be more flexible with your design. A lot of things in our design started from this, which meant we went down a certain route.

We would still have the same advice for those considering using CLT as we had in this post back when it seemed that disaster was afflicting our build in January 2016: DON’T start building in the Fall in a climate like this, DO wrap your CLT structure in a breathable, water-proof house-wrap as soon as it’s up.

The roof might also be something I would rethink were we starting again. We designed it to fulfil several functions: to be at a good angle for generating solar power in the shoulder seasons and winter, to provide shade for the upper storey windows in summer and of course to be able to contain enough insulation. Originally, we were not going to use CLT for the roof, but the horror stories we heard about thee practices of truss manufacturers around here convinced us to give it a go. With CLT roof panels, we got added structural strength, which will mean the weight of any number of solar panels is no problem, however we had to have a floating rafter design (and here) in order to retain the overhang. This looks beautiful but it was very complicated to engineer and caused the insulation installation to be much more difficult – and cutting the wood fibre insulation we used into exactly-sized triangular sections was not easy (especially in the depths of winter). Had we started with CLT as our primary material, we might have made different decisions here: we could have gone for entirely different roof designs, and gone for ground-based solar panels, and considered other ways of shading. However, just aesthetically, I really like our roof and I like the fact that it goes against the grain of having roofs finish flush to the walls.

In the end, we have a beautiful, sustainable high-performance passive house, which we love and which works. It was a long journey getting here but it was worth it. We will keep occasionally updating this blog with things that we are doing (we’ve still got a solar PV system to install in 2018 for a start) and performance updates, but in general there probably won’t be more than a post a month in 2018. And we’re always very happy to be contacted with questions from other people considering building sustainably.

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Passive Cooling

As our place is a passive house, it is pretty much sealed tight in the colder months and works via a mechanically very simple Energy Recovery Ventilation (ERV) system from Swiss manufacturer, Zehnder. As regular readers will know, we added a 2kW heating element (about the size of a toaster) which turns the system into a very gentle (un) forced air heating system. This is all we have and need by way of heating.

So what do we do now it’s the summer and it gets hot? We unequivocally do not have Air Conditioning (AC). Okay, we are in Southern Ontario and this is not a tropical climate. But we started from the principle that we wanted for this to be a Net Zero house not just a Passive House. So, thinking about cooling was also designed into the place.

In some ways the answer is laughably simple: in the summer, we open windows. However, as you’d expect, exactly what’s going on is not quite as simple as that.

  1. Reducing passive heating. First of all, we have very large windows on the south side of the property in order to passively heat the place in the colder seasons, but we don’t want those window to heat up the house in summer. Of course, in summer the sun is higher in the sky which means that it can be relatively easily prevented from hitting windows, even big ones, directly by having enough shading. Together with our architect, we worked out the overhang needed on our roof and the width of the porch that would be needed to provide summer shading but allow the sun in at other times. Considering all the trouble the builders went to getting our rafters in place and all the insulation to fit in perfectly around them, it’s particularly satisfying that this works exactly as designed!
  2. Thermal mass. Look at cave homes. Why do they stay cool? Because of the thermal mass of the earth / stone around them. You can still design houses for thermal mass, even if you don’t want to live in an actual cave: rammed earth, for example is an amazing building material for (very) hot climates, and one we considered early on (see here). But there are plenty of good modern versions based on this principle. Our house is a combination of solid wood (CLT) and wood fibre insulation, which isn’t in the same league as rammed earth or stone for thermal mass, but is good enough to make a difference in our not-quite-so-hot summer temperatures.
  3. Air flow. There are two basic ways to take advantage of physics to create natural through-flow of air in a house to provide significant cooling. Our house is designed for both.
    • To cool a particular room or floor, cross (or wind) ventilation is the easiest answer – this means taking advantage of pressure differences at one side of a building by opening a window (or two) open at each end of the space you want to cool. You can encourage this process with ceiling fans and/or ceiling fans (and the latter may be a good idea if you live in any area where you don’t feel comfortable leaving downstairs windows open). Our cross ventilation is designed to make sure the air exits through the toilets and the pantry, which has the added benefit of removing air directly from places that need it most.
    • For whole house passive cooling, you need to think about stack ventilation (and/or the related Bernoulli’s Principle). There is a really good explanation of both here, but simply put it means taking advantage of the pressure differences and wind speeds at different heights, so cool air enters the house at lower levels and hotter airs exits through the highest points. Our attic has two windows at either gable end these are open all the time in the summer, day and night.

Cross ventilation (image from Sustainability Workshop)

Stack ventilation (image from Sustainability Workshop)

The particular windows that open themselves are European tilt-turn opening windows. They can be fully closed, fully inward-opened, or tilt-opened, which means that they are still locked but have enough of a gap to allow air flow. Because our internal doors are designed with the air flow for the HRV in mind, they also have enough of a space underneath for summer air flow. The one small problem we had to deal with was the lack of insect screens – European windows generally don’t have them, because clearly they never had to deal with the number of flying creatures we get on the edge of Lake Ontario. If we had had them manufactured as part of our original window order, it would have been ridiculously expensive. So we just got a local manufacturer to fabricate some to order. They were slightly bemused by our request for screens that had to be friction-fitting – i.e. not for pre-made slots or clipped in etc. because we don’t have anything like that – but eventually they worked out that the best solution would be to simply make the screens very slightly smaller all around and put heavy-duty stick-on weather-stripping all the way around. It works fine. We couldn’t get a colour to match our dark red frames – they only do brown or white – but the brown doesn’t stand out, and at less than $900 for all the screens we aren’t complaining

Tilt-turn windows (image from http://glowindows.com)

So, yes, we open the windows.

And does it work? The short answer is ‘yes.’ As we discussed in a previous post, both our passive house advisor and the researcher who analysed the winter performance of the place argued that we would need mechanical cooling in summer. We aren’t going to say that they were wrong yet, because it hasn’t been the hottest summer ever so far. But we haven’t felt that we needed even the most basic fan so far and from casual readings of the temperatures, they are not getting anywhere near the 26ºC inside that is apparently the threshold for needing mechanical cooling. In fact, when it’s in the high 20s outside, it is still in the low 20s inside the house.

Our conclusion is that for Ontario, energy-draining AC is completely unnecessary if your house is designed sensibly. And that may well be true for much hotter climates too. There are good traditional examples of thermal mass design and natural ventilation from all over the world, but he changes we need can also be combined with technical innovation. Most architects, engineers and builders already know how to build houses that work without excessive energy use, but the current housing (and wider) market provides incentives in the opposite direction, while we know that we have to act fast to prevent the worst that will come from global warming. My view is that we need significant government intervention in housing policy. The governments of some hotter countries are taking this more seriously – look at this Australian government site, which is packed with good advice on passive cooling: http://www.yourhome.gov.au/passive-design/passive-cooling

However, it may be that we just have to stop building ridiculously in (and even abandon) certain large cities in completely inappropriate places. In North America, Houston, Las Vegas, and especially Phoenix are totally unsustainable and will only get worse. Phoenix is, I think, the fastest growing city in the USA, particularly popular for retirees, and yet it’s likely to be so hot (and lacking in water) as to be virtually uninhabitable in a hundred years or so: http://www.salon.com/2013/03/14/tk_5_partner_5/ (just one of many articles on the subject, and there are academic studies on which this is based). In those places, designing for passive cooling is going to be a matter of life and death not just comfort, in a post-oil world. It’s a daunting prospect.

Preliminary winter performance data

We have had temperature and humidity data recorded in the house over the last 4 months as part of a project conducted by Anthony Mach, a passive house designer and Building Science research student at Algonquin College. The preliminary data is now available, courtesy of Anthony. What we have here is essentially the raw temperature and humidity records in two locations: one in the middle of the open-plan downstairs space (1st Floor), and the other upstairs on the landing (2nd Floor). There is a lot of analysis to be done with this data combined with other data on external temperatures, energy use and so on.

A few things to note when looking at these charts:

  1. We were only half-moved in for most of November – we started using the kitchen sometime in the second week.
  2. When we moved in (around the 21st November), the HRV (which actually turned out to have an ERV core – for more on the differences, see here) had still not been properly balanced and we were still only using the system on its lowest setting.
  3. After the HRV had been balanced properly on the 4th December, we started using it on the middle setting, with boosts after baths and during cooking.
  4. We only had the 2kW Thermolec heating element, that works with the HRV, installed on December 14th. Up until that point we had only been using a single 1kW space heater. If it was cloudy in the morning after this point we used both, but if it was sunny we didn’t need the later.
  5. However, that installation coincided with a serious cold spell where external temperatures dropped to -25ºC or lower.
  6. We were away from the 20th to the 30th of December, and had the HRV just ticking over, which means that the house would have had almost no internal heating. You can see the drop, but what’s remarkable is that the place still never got below 13ºC.
  7. Once everything was back to normal and functioning properly, from early January, the temperatures in the house were generally between 17ºC (average night-time low) and 19ºC (average day time high) upstairs, with the extremes being 15.5ºC and 21ºC; and 18ºC (average night-time low) and 20.5ºC (average day time high) upstairs, with extremes of 16.5ºC and 22ºC. The difference is probably explained by a combination of the use of the extra heating downstairs, the passive solar effect from the larger windows, and generally that there is more activity downstairs for more of the time.
  8. The humidity has generally been where you’d want it, between 40 and 50%, gradually drying out as winter goes on. Our HRV having an ERV core helps in stopping the place getting too dry.