Q: What is the payback on the Photovoltaic Modules (solar electric panels)?
A: About 2%. Right now, with the province of Alberta placing no additional value in green energy, we’ll get paid roughly 10 cents per kilowatt hour (optimistically). The reasons for putting these up are not monetary. If the province ever starts charging coal-fired power plants for poisoning our air and water with mercury and other toxins (not to mention carbon dioxide), the economics will improve significantly.
Q: What will you use the loft for?
A: We added the 300 square foot loft after discovering with our computer model that it would only cost about 400 kWh/year extra in heat energy. That’s about 1.5 Gigajoules. Since it will only be accessible via a ship’s ladder, our loft can only be used for storage according to the building permit. However, I could see other people in other houses using such a loft for a home office, kid’s play area, or someday for another bedroom if circumstances dictate multi-family living.
Q: What happened to the window?
A: I broke it okay? Leave me alone, I’m going to my happy place!
Q: Won’t the house overheat in summer?
A: Since our movable awning will prevent most of the June and July sunshine from entering the home at all, summer isn’t the problem. October is the problem month – the month when the sun is low enough to come under the awnings and yet the outside temperature isn’t cold enough to keep the house cool (given our high levels of insulation, especially). We’ve mitigated the overheating risk by adding 10-12 tonnes of concrete per floor as thermal mass. Since the concrete is directly exposed to the living space, it absorbs excess heat relatively quickly. This should make the living space more comfortable on a sunny October day when it’s 12 degrees outside. Furthermore, the movable awning will hopefully shade our windows in October more than a fixed awning would, further decreasing overheating.
Q: How will you finish the concrete floors?
A: We won’t be covering them with cork or wood, as either material would insulate it away from the living space, thereby negating most of its benefits. We’ll dyeing the concrete and then sealing it with a water-based sealant.
Q: Won’t the concrete be hard/cold?
A: The concrete will definitely be harder than hardwood or cork. It will also feel cold at times. We’ve made a choice to adjust to living with concrete floors. We always wear Crocs around the house anyway, a practice that will continue in our new house. Also, we’ve considered having a big basket of Crocs at the front door for guests. We’ll also put rugs in strategic places - places that add comfort, such as at the foot of a couch, but don’t cover too much of the floor, (which would negate some of the thermal benefits that concrete has for our passive solar design).
Although relatively rare in Canada, living on concrete is common in many other countries. Also, keep in mind that the concrete floors will sometimes feel warmer (in winter) and cooler (in summer) than a regular floor would, making it more comfortable some of the time. Overall, with its ability to regulate temperature in the living space – cool it in summer and warm it in winter – I expect the concrete floors to be a net contributor to our comfort.
Q: How much will this house cost?
A: Although we won't know the exact cost until it's complete, we're estimating a cost of $500,000 - $550,000 excluding the land. That is a big chunk of money, but keep in mind that any custom-designed, one-off house built in the middle of the city will cost upwards of $450,000. The construction is also very high quality. Many builders that build dozens of houses at the same time on the edge of the city cut a myriad of corners that were not cut here. Everything from waterproofing details to well-built window wells was well done on this house.
Q: What is the incremental cost to reach Net Zero?
A: We spent $20,000 to get 85% of the way to Net Zero (versus conventional construction). Given that the province now awards a $10,000 grant to houses that achieve an Energuide rating of 86, which that first $20,000 would achieve, every new house should spend that first $20,000 ($10,000 after the grant). We then spent about $55,000 to reache Net Zero.
Q: Why did you choose to not be connected to the natural gas grid?
A: When you build a home this efficient it makes sense to disconnect from either the electric or natural gas grids because of the very small need for external energy, and the high monthly subscription costs of being connected.
Since the best way to "store" electricity is by selling it back to the grid, and since we have the ability to manufacture electricity onsite (unlike natural gas), the natural gas grid is the obvious choice for disconnection. It costs about $350 per year to be connected to the natural gas grid, and we only need $50-$75 per year of natural gas energy.
Q: Why did you not use geothermal heating?
A: Since we are going to be disconnected from the natural gas grid anyway (see above), we gave serious consideration to heating with a ground source heat pump (geothermal heating). I discussed geothermal here (the gist: if you need lots of really efficient heating, save your $30k and stick with natural gas) and our choice of heating systems here.
In short, the house requires so little heating energy (~2400 kWh per year) that we decided to go with electric radiant heat for a small fraction of the cost and complexity.
Q: I'm not sure that I understand why the home would overheat in October. If it's 12C outside and too hot inside, coudn't you simply open a window or turn off the heat-exchanger for incoming air? Wouldn't this be simpler and more cost effective than adding more concrete?
A: October is the worst month because the sun is so low in the sky that most of its rays won't be shaded by traditional overhangs, and because it's not cold enough outside to extract sufficient heat from the house through the (super-insulated) walls.
Good point about opening windows. It's the exact strategy that Peter Amerongen always suggest when I express concern about overheating. However, it's ideal to design a house to be comfortable without the direct participation of the occupants. Furthermore, if we had no extra mass and came home to a house that was 29 degrees on a late October day, it would take quite a while to cool off.
Most importantly, though, opening the windows is wasting the potential solar energy that the overheating represents. The solar mass provided by the extra concrete saves us (helps us to generate, actually) 2164 kWh (7.8 Gigajoules) of energy per year. It does so by storing solar heat until it's needed, in the middle of the night on the cool October day that you mention. More details here and here.
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