Category Archives: airtightness

HRV Fan Failure: the importance of pre-heating in cold climate zones

We’re in our third winter in the passive house (the second full winter, I guess, since we were only in for part of the first and a lot still needed to be done back then). Several issues have emerged, which are all things that are fixable, but which in retrospect could and should have been prevented. The main one of these is that about a month ago, one of the fans in our HRV failed suddenly, which left us without ventilation in the middle of winter. Up to this point, the Zehnder HRV* has been completely hassle-free – you’d hardly have noticed it was there at all.

This is when it suddenly turns out to be very important that there is a reliable local dealer for your HRV company… and, there isn’t. Pinwheel, who supplied us our system, ceased being an official Zehnder dealer pretty soon after we got our system and despite there being officially named companies that have some affiliation in the province, none of them actually supply or repair Zehnder. Luckily, Zehnder North America have awesome people in their main offices who are prepared to go the extra mile for a customer.

I chatted to a couple of different people, the first, Joe from Operations, about the possible causes of the failure and what we needed. Zehnder agreed to send us a replacement fan immediately with no charge. Excellent. But then what to do about the installation? Well, basically, they got another guy, Gary, the Training and Service Manager, to walk me through it. Yes, I did it! it wasn’t that hard, as it happens, although there were some electrical circuit operations to perform that had to be done exactly right and safely, but I wouldn’t have been able to do without him. I’m pretty confident I could do it again now, if I had to. Gary – you’re awesome!

As to why this happened… well, it’s highly likely that it was something to do with the low incoming air temperature. We noticed when we were installing the system that Zehnder HRVs are not guaranteed below a certain temperature. Apparently Zehnder would never recommend installing one without a preheater, but no-one involved in our original installation – not our passive house advisor, not the dealer and not their contact at Zehnder at the time, ever mentioned this or suggested including a pre-heater. Everyone seems ‘surprised’ now that it somehow didn’t happen. So, a take-away for anyone building a passive house in these cold climate zones: you need a pre-heater for your HRV — don’t forget it or think you can get away without one.

Anyway luckily for us, Zehnder has recently changed the way it does pre-heating for its HRVs anyway. Instead of an internal pre-heater, they now supply an external model that sits in the intake duct. So, we’re installing on of those, and hopefully we’ll have no further problems with fan failures.

I’m still thinking about the implications of all this. A sudden HRV failure makes you very aware of just how much the passive house concept depends completely on this mechanism, and however reliable the mechanism you have, this dependency is a large weakness, a major lack of resilience. On the other hand, we did find that ventilating the house by opening windows for half and hour a day works even in winter when it’s -20ºC outside without cooling down the house too much. We’d been super-paranoid about opening doors for even a few seconds before and, actually, it was fine. We also used a dehumidifier to get rid of excess moisture.

Anyway, a big thank-you to Zehnder North America for their support. They really are a great company – if only a decent Ontario company would take up the challenge of being a proper dealer and servicing agent…

*Zehnder Comfoair 200 UL (Luxe) ERV. You can see more about the system installation here.


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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.

Warm Inside

The coldest night we’ve had in the passive house so far saw the outside temperature drop to -20ºC (and that’s before we take account of wind chill). However, inside it was 15ºC when we got up, and with a couple of hours of the little room heater and the sunshine today, we’re now up to 19ºC. Plus, the place feels much warmer than this. It’s hard to describe what this means over and above physical temperature, but it’s something to do with the evenness of the temperature and the aesthetic warmth of the wood.

One other issue, apart from the Motura door seal which we discussed yesterday, is the lock on the front door. This might be passive house certified and highly insulated but the lock is essentially a metal tube which goes from one side of the door to the other, in other words a cold bridge surrounding an air leak. It might be a very small example of both, but the ice that forms on the inside of the lock when it’s as cold as it was last night, shows the truth!