Tag Archives: heat recovery 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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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.

“The most airtight building in Ontario”

On Saturday, our advisor and supplier, Malcolm Isaacs from the Canadian Passive House Institute, visited us again to carry out the second (and hopefully, final) blower door test on airtightness, and to do some final tweaks to the Heat Recovery Ventilation (HRV) system to make sure it is fully balanced.

On the latter issue, we discovered one curious thing: our ‘HRV’ actually appears to have an Energy Recovery Ventilation (ERV) core. This means it actually not only uses a heat exchanger to transfer heat from the outgoing care to the incoming air, thereby keeping the air in the house both warm and fresh, but also balances the humidity (for more on the differences, see this Ecohome.net article). This is interesting not least because we only paid for an HRV, so far as we know…

However, the big news is something much bigger. When Malcolm last visited to do our preliminary blower door test at the end of September, various things weren’t ready, in particular, we had a malfunctioning and only partly sealed Motura sliding door, and the equipment wasn’t able to accurately record the figures we needed so we could only get a rough result. Even then we got a pretty good indication that the house was already well inside the Passive House standard. In the meantime, the door had been properly sealed, and Malcolm had obtained the component that would allow for the test to be done more accurately.

As the house was being pressurized, we went around with a little camera that measures temperature differences, to check for air leaks. We also discovered that one of the HRV ducts that goes through the outside wall was not actually as sealed as it should have been, despite the gaps between it and the wall having been filled with sprayfoam. So we had to seal up the edges with some more of that expensive but very effective Siga tape.

The process of doing a blower door test is outlined in the blog entry about Malcolm’s previous visit. You need only recall that you pressurize the house to 50 Pascals, and then record the amount of air that has to be added to the house to maintain that pressure. From these numbers, with the house volume, you can calculate the Air Changes per Hour, or ach50. The highest Canadian Standard, R-2000, is 2. The Passive House standard is 0.6. Last time we’d measured just above 0.4.

Malcolm did his measurements and then went away to do the calculations back home. From here I’ll just quote directly from his e-mail to us today:

“I’ve just finished recalculating the blower door test results from my visit yesterday. We did not do too badly, with an overall n50 airtightness of 0.185 ACH @ 50 Pa for both overpressure and underpressure. To the best of my knowledge this house is the most airtight building in Ontario […] This result shows the high quality and performance of all components used in the house, as well as the significant extra efforts of each of us who worked on the airsealing. The impact on overall energy demand in PHPP [the software used for calculating Passive House performance] is very significant: it drops overall specific energy use from 14.6 kWh/m2y (assuming 0.6 ACH)  to 12.5 kWh/m2y.”

For those of you who don’t speak Passive House, Malcolm provided a summary:

“Speaking as an engineer, we have a special technical term for this result: KICKASS.”

Quite. 🙂