Here are our current statistics for our Net-Zero Energy House. During the time period, we had 7 occupants in the house, and during two of these months, we had between 10 and 12 people occupying the house as we hosted two families. In addition, a home office with two computer servers running 24/7 added to the electricity usage not normally associated with a residence, as we estimate a 2500kWh annual consumption on these two computer servers.
Electricity – From March 17 2011 to March 19 2012 – 27536kWh of usage, from PowerStream’s utility bill.
Gas – From construction to March 29 2012 – 282m³ of natural gas, converting to 3062kWh, with about 1/3 of which was used for “burning in” of the fireplace.
Total Energy Consumption – less than 30,600kWh consumed in the first year of occupancy.
Electricity Generated – Our 34kW system should generate the 30,600kWh that we consumed in the first year of occupancy. Generation started on May 5th, 2012, and as of March 11th, 2013, we have generated just under 26,000kWh, with the next 50+ days as being typically the highest production days of the year.
The original architectural design called for a combination of stone and stucco for the exterior of the house. But considering the majority of the house was wrapped in ICF and EPS, the most logical choice of material was stucco, as it required an EPS substrate. After we had priced the stone installation, made more difficult with the ICF and EPS as the surface material was not structural, we decided to change the design to an all stucco exterior cladding.
Our choice was to use the Dryvit TAFS (textured acrylic finish system) on the ICF, primarily because of their TerraNeo finish, which gave it a granite look without the cost of stone. Dryvit is one of the leading stucco systems manufacturer in the world, and their TerraNeo finish has chipped granite flakes in the mix to give it a more interesting and pleasing aesthetics for accent areas, a combination that gave it a very unique look, and a glimmer and sheen that can be seen at varying sun angles or on an overcast day.
Cork flooring was chosen for about 70% of the floor space, except for bathrooms (where we used tiles and/or stone), and the living/dining/office, which we went with a traditional hardwood.
The cork flooring has a very unique pattern that doesn’t resemble traditional hardwood, one that you either love or hate. In our case, we chose function and comfort over esthetics (not that we mind the look), as the cork floor is a softer, warmer, and overall more comfortable floor to stand and walk on. The randomness of the pattern allows scratches and scuffs to be less visible. A side benefit is the sound absorbancy of cork, which should help dampen the sound travelling throughout the house.
We had considered a slate floor for the family room, kitchen, and dining room areas, where it would have benefitted from the thermal mass effect of the winter sun shining on the floors as these rooms were south facing, but in the end comfort won out, and cork it was.
Our flooring was sourced from Jelinek Cork Group in Oakville, one of the oldest cork companies around. We chose their Sierra Brown in a floating style floor, with a further 2.5mm cork underlayment.
Installed costs were about $7.50/sqft (at list price), similar to hardwood flooring.
CaGBC LEED for Homes – Points can be acheived in Material and Resources, in Environmentally Preferable products (MR 2.2).
The goal in a passive solar design is to have the sun supplement the heating of the house in the winter while rejecting the sun in the summer. This is primarily achieved by designing south facing overhangs over windows such that it would allow the lower sun to enter through the windows into the house during winter months, but as the sun rises higher in summer sky, it rises over the overhangs such that the direct sun is kept out of the windows.
Variables include the location and orientation of the house, how tall the windows are, and how far below the overhangs the windows are. In our case, we worked out to about a 28″ overhang (24″ + 4″ eavestrough), which would allow 90%+ of the sun in when the sun is at its lowest during winter solstice (where the sun is lowest in the sky), and would completely block the sun during the summer solstice (where the sun is highest in the sky). The picture on the right was taken in late July at about 3pm, and you can see the shadow line is not protruding into the house.
In addition, choice of materials inside is also important, as darker and denser materials are better at absorbing the sun rays than lighter materials. Slate or granite tiles, for example, would be perfect for this application, but in our case, we’ve chosen to use a medium dark stained cork flooring to gain some of the benefits of the passive solar design without giving up any comfort of the softer floor.
The windows that face south also has to be tuned to allow for greater solar gain, measured and represented by a solar heat gain coefficent (SHGC), usually at the expense of the R-value of the windows. In our case, our south facing windows had a SGHC of 0.44 compared to 0.26 for the rest of the house, at the expense of the R-value, decreasing from 5.5 to 3.8. However, the heat gain, even in the winter, will more than compensate for the relative increase in heat loss between the two different sets of windows.
Update- In real world observations during 2011, we have noticed that on winter solstice, the sun can reach as far as 15′ into the house from the window, heating the floor and its contents for free heat in the winter, while during summer solstice, the sun reaches just the window sill, reducing the cooling demand by having very little sun inside the house. Since our house is on a smart meter with hourly usage statistics provided by Powerstream, we have been able to correlate the time-of-day usage with Environment Canada hourly weather statistics, and the heating demand was reduced by an astonishing 25% when the sun was out. Our house is not the most aggressive design for passive solar, so much better gains can be achieved by simply orienting and sizing windows and soffits and choosing materials that can absorb heat in the winter.
This entire project began with the announcement of the renewal energy program that the province of Ontario had plan to implement in April of 2009, and the feed-in tariff that was to be offered. In looking at what the best method to take advantage of the program was from a small scale perspective, we quickly realized that it would be cash flow positive from the solar panel investment, and that it would help pay for some (if not all) of the additional energy efficiency upgrades for the house. This became the lynch pin in this entire project from an energy perspective as well as from a financial perspective.
We began by looking at lots that were on streets with an east-west direction fronting on the south side of the street that were as wide as possible within our budget, while still fitting our personal requirements for area amenities. We were fortunate enough that, within a very short period of time, we were able to locate and secure the purchase of a 100′ wide lot in a suburban area of Toronto. Our next step was to design the house to maximize the roof space available for the solar panels, and in doing so we included four design aspects for this purpose:
The first was to specify that the roof pitch for the south facing portion of the roof to be an 8/12 rise (33.7° pitch), which was within a couple of degrees of optimal for our geographic location.
The second was to set back the 2nd floor rear wall so that the south facing roof could extend from the top of the first floor all the way to the ridge (see architectural drawings).
The third was to use two gable ends instead of a hip roof to maximize the south facing roof.
The fourth was to incorporate a tandem garage; this allowed us to add roof space and storage space without increasing the conditioned area of the house.
By incorporating the above design aspects, we were able to design a roof with over 2,300 sqft of area to mount the solar panels, which allows us to mount a 30kW PV system, very likely to be the largest roof mounted residential system in the province. In comparison, most approved systems for residential mounting in this region has been in the 6kW-8kW range, with many being as small as 2kW-3kW.
We chose to work with Honeybee Solar based on their knowledge, and their willingness to look at source different solutions, and in our case, panels and inverters that will allow us for the greatest payback. The panels are from CEEG and from Eclipsall, about 15% panel efficiency, while the inverters will be from Aim Energy (local Ontario content) through Honeybee Solar, which provides some of the highest yielding inverters on the market. In their test site in Southern Ontario, they were able to generate over the course of a year 70% more power on a flat-straight-to-the-sky panel installation than a typical DC installation. In real world use, we are expecting about 1.3kWh/W of panel, a 25-30% than a traditional string inverter installation.
Our system of about 30kW will cost somewhere in the neighbourhood of $200,000, but the 20 year contract that the Ontario Power Authority offers for a system of this size will pay back $0.713/kWh, and we anticipate we will generate more than $30,000/year. In a pre-tax calculation, on an annualized basis, this would offset close to a $450,000 mortgage based on a 20 year amortization and a 2.99% interest rate (as of July 2012).
Total production is anticipated to be around 40,000kW/h per year, of which we anticipate about half will be used by the house for daily electrical uses as well as for cooling, and the other half will be used for heating in the winter using a combination of our Daikin Altherma heat pump as well as natural gas. Our calculation includes the BTU used by burning the natural gas, converted to kWh.