This is something I’ve been wrestling with since we decided on building a super-insulated, highly energy efficient home. And really this is something that I think a lot of builders, architects, and designers of eco- and green homes have been debating about since the Passivhaus concept came to North America in the past few years. When we initially got going on our project I was pumped on the possibility of ‘not needing an active heating system’ – as Passivhaus enthusiasts have touted their homes on. However, that really is not quite true.
Although many of these Passivhaus homes in Europe don’t necessarily use a boiler or furnace as we do in Canada, they do still technically require some way of heating. Often that is a heating coil attached to the existing ventilation unit that warms the incoming ventilated air. For our house, the possibility of using such a system simply made no sense. Passivhaus often justifies some of its standards on “user comfort.” Certainly I agree that user comfort is critical, however, in order to meet some of the rigorous standards of Passivhaus, people have tended to sacrifice comfort to meet the certification. For example, in our project, indeed, we could have used this method of heating as a secondary option, but it would not be sufficient to meet all of our heating needs despite the super-insulation. Furthermore, we need a thermal mass (concrete floor) to take advantage of the solar gains to cut down on our heat load. Those of you who have walked around on a cold concrete floor know that this is pretty uncomfortable (as a physiotherapist, I cannot count the number of people I see who complain about knee, back and foot pain due to walking on concrete floors at work). That being said, a warmed concrete floor is very pleasant, and strangely comfortable. Given that we wanted a concrete floor for both thermal mass and aesthetics, it made no sense to me not to use in-floor hydronic heat. In this case, we had to choose user comfort over Passivhaus standards.
Another major criticism of Passivhaus standards is both the annual energy consumption and annual heating/cooling consumption standards. These standards are very strict at 120 kWh/m.sq./yr and 15 kWh/m.sq./yr. I’ve previously written about these as well. But is this actually possible to attain in a very cold Canadian climate? Indeed this has been shown to be possible in a handful of projects in Canada. But not that many. Why is that? Recently we’ve run our numbers through the HOT2000 software, which is a Canadian software for energy efficient homes to calculate energy consumption. It’s not as thorough as the PHPP Passivhaus software, but it’s pretty good, and a lot cheaper to have done.
Ok so here are our numbers:
House size 1240 sq.ft (main floor) + 1240 sq.ft (basement) = 2480 sq.ft of treated floor area = 230 m.sq of total treated floor area.
Estimated Annual Space Heating Requirement: 7159 kWh / 230m.sq. = 31.13 kWh/m.sq/yr
Estimated Annual Electrical Space Heating (minus expected wood stove use): 2342 kWh / 230 m.sq. = 10.18 kwh/m.sq/yr
Estimated Annual DHW Heating: 3409 kwh
Estimated Annual Appliance: 8760 kWh
TOTAL ENERGY CONSUMPTION: 19,328 kWh / 230 m.sq = 84.04 kWh/m.sq/yr
First let me explain a couple things. One, we expect to use our wood stove a lot in the winter. I love a wood fire, there is something incredibly comforting about watching wood burn. Two, I do think that the annual appliance use is on the high side and I would also argue that our total space heating is also a bit high when comparing it to the Mill Creek NetZero house, an eco-house project
using the same wall system in a similar climate. Nonetheless, let’s give these numbers some context:
Our House Projected Annual Space Heating = 31.13 kWh/m.sq/yr
Our House (minus wood stove heat) Annual Space Heating = 10.18 kWh/m.sq/yr
Passivhaus Annual Space Heating Standard = 15 kWh/m.sq/yr
Ok, so you can look at the comparison numbers I’ve provided above for Passivhaus and the average Canadian home versus our place at 31.13 (overall heat requirement) and 10.18 (electrical space heating requirement). Both of these numbers are A LOT less than the Canadian average. I’ll use the 31.13 number because it is the highest possible use we would need in an extremely cold year without using any wood heat. That is 77.3% less than the average house in Canada! Pretty awesome! And yet, it is twice as high as the Passivhaus standard!!
I’ll remind you that we are using the following: R100 ceiling, R56 above grade walls, R32 below grade walls and R32 under slab insulation. We are also having significant south glazing and minimal north glazing. We will be installing the highest efficient fiberglass windows and we expect the airtightness of the house to meet the Passivhaus standard of 0.60 air changes per hour at 50 pascals. So, WTF?
The bottom line here is that Saskatchewan is a lot friggin’ colder than Germany. The number of heating degree days in Germany in 2014 was 3100
. The number of heating degree days in Saskatoon in 2014 was 6035
. Well, that’s about twice as much, which would account for our need for twice the heating load – makes sense! Therefore, I have a hard time understanding how the standards of German Passivhaus can be applied to a very cold Canadian climate.
If we look at the overall Total Energy Consumption (84.04) however we are actually significantly lower than the Passivhaus standard of 120. This begs the question of, in Germany, what is accounting for the 105 kWh/m.sq/yr difference of energy if not for heating? Is their appliance and hot water use that much higher? Or is this particular standard higher to account for the larger homes and buildings that are typically built with Passivhaus? (This brings up another criticism of Passivhaus penalizing smaller homes. Check out this article for an exhaustive list of criticisms of Passivahus in North America
. Passivhaus US and Canada have recognized the limitations of the European standards and are taking steps to try to modify these to be appropriate in North America. However at this time, the standards are still up for debate).
Anyways, what do these numbers really mean, except to compare apples (Germany) to oranges (Saskatchewan)? We weren’t going to be pursing Passivhaus certification anyways (at an approximate $10,000 price tag for certification, I’d rather put that money into solar panels). But I think it provides an interesting discussion. In the end we will be building a highly efficient, super-insulated house that will consume about 75-80% less energy than the average Canadian house. We truly won’t know our overall energy consumption until we actually live in the house so all of these numbers are a bit arbitrary.
Yes, you can build a “true” Passivhaus on the prairies, but you’d be looking at making huge financial investments and sacrificing comfort to meet the standards.
I’m reminded of a discussion I had with a local energy efficient home builder recently. He said: “Anyone can build an extremely energy efficient house with enough money. But to build one on a budget, now that is something impressive.”
In the end, we are building on a budget, which should come in at or below the cost of building your average stick framed house and our energy bills (100% electric) should be in the range of $100/month. I think I can live with that.