Sustainable Building Program and Courses at The Endeavour Centre

The south facing roof surface of Canada’s Greenest Home just got busier capturing the energy of the sun with the installation of our solar hot water system.

Two collectors and a small PV module adorn the shade roof between the first and second floors. The system will provide between 50-75% of the home’s hot water needs.

The two 4 x 8 foot collectors should be able to provide between 50-75% of the hot water needs of the home, taking a very large burden away from other forms of heating. Most reputable estimates in our climate show that the heating of water can account for 20-30% of total energy use in a home, so by offsetting this demand with solar hot water we will hopefully be reducing overall energy use by 10-22.5 percent, which is quite significant.

The system we chose (installed by Flanagan and Sun) uses the two collectors plus a small PV panel mounted next to the collectors to power the pump (this ensures the system works if there is no grid power, avoiding overheating in the collectors if the power goes out). Solar hot water is a very simple system, with a series of copper tubes on a black metal collector plate in an insulated box behind glass. An anti-freeze solution (propylene glycol) circulates through the tubes using a solar powered pump and absorbs the sun’s heat. The hot fluid moves to a heat exchanger next to the hot water tank, where it gives its heat to the water in the tank and returns to the collectors to gather more heat. It is a very effective use of the sun’s energy.

The heat exchanger and solar pump are in the orange box next to the storage tank, where the heat is given to the water in the tank. To the right is a drain heat recovery unit, that uses outgoing hot water to pre-warm incoming water to the tank, further reducing heating needs.

The heat exchanger warms the water in the tank by thermosyphon, which means that the cooler water at the bottom of the tank is exposed to the hot tubes from the collectors. As the tank water gets warmer, it also gets less dense and will rise to the top of the hot water tank. This type of heat exchange does not require any additional pumping and has no moving parts to wear out. It also ensures that the hottest water is always at the top of the tank where it will be first to be used. The water in the tank can stay quite stratified, meaning that there can be a layer of very hot water at the top of the tank with much cooler water right below it, and because the water is drawn from the top of the tank the homeowner can have a hot shower even if the solar collectors have not been active for very long.

The tank in our system is an 80 gallon tank, and it is used just for storage of the solar heated water. The water from this tank will move through an electric on-demand heater that can sense the temperature of the incoming water and add only the amount of heat required to bring the temperature to the desired level. If the water in the tank is hot enough, the electric heater will not turn on at all. We’ll blog more about the on-demand heater when it is installed…

Solar hot water used to be considered the best “investment” in renewable energy, meaning that it had the largest impact on energy bills for the lowest financial outlay. The recent drop in PV panel costs have taken a lot of focus away from solar hot water, as in some regions (like Ontario) the subsidies for PV power can make it a better investment to install enough PV to run an electric hot water heater. However, solar thermal makes direct use of the sun’s heat in a way that is not linked to grid-tied power and to rate fluctuations. As long as the sun shines, hot water will be the result, and for that reason we still see an important role for solar thermal in a project like Canada’s Greenest Home.

One of the most important – but least glamorous – of the features of Canada’s Greenest Home (and most natural and sustainable buildings) is the vapour permeability of the walls. It doesn’t sound like a big deal, but it’s a major difference between conventional building and so-called alternative building and represents a very different way of thinking about building performance that can have important performance ramifications. What follows is a simplified explanation of this difference. For more detailed information, I suggest the excellent material available for free at BuildingScience.com.

The “moisture balance” is the key to healthy walls… making sure that incoming moisture is able to leave the wall at a rate that avoids build-up and damage.

To understand the difference, one must first know that moisture will always move from areas of high concentration to areas of low concentration (a variation of the “nature abhors a vacuum” principle). For the majority of the heating season, this means that moisture is trying to move from our warm, moist interior spaces into the outdoors, where it is cooler and drier. If there are leaks or holes in the building enclosure, this warm moist air will move quickly. But even if there are no leaks or holes, this moisture will still migrate to the exterior by diffusion – a molecular movement of moisture through the materials of the building. A material’s ability to resist this diffusion is known as its permeability. Materials with low permeability ratings allow very little moisture through, and materials with high perm ratings can allow quite a bit of moisture through.

Okay, that’s a lot of words to say that there is a natural vapour drive through the enclosure of a building.

For the past few decades, mainstream buildings in northern climates have relied on a vapour barrier – basically a thick plastic sheeting – to prevent air leaks from inside to outside and to prevent the diffusion of moisture into the wall. This practice arose from the failures of many early “air tight” homes, in which moisture was able to accumulate in the wall cavities and resulted in rot and mold issues. The solution was to use a vapour barrier membrane on the interior of the walls to prevent this from happening.

In the natural/sustainable building world, we have always preferred to use wall assemblies that are vapour permeable. This acknowledges the fact that the vapour drive in buildings is inevitable, relentless, and not necessarily a problem unless materials are introduced that do not allow for this vapour to pass through at a reasonable rate. A good example of such a material is OSB (chip board) or plywood, the two most common exterior sheathing materials in conventional construction. These materials will resist the migration of moisture such that it can accumulate and condense on the interior side of the sheathing and begin to cause problems. If moisture can’t pass through the exterior sheathing, it must be prevented from entering from the interior side… hence the plastic vapour barrier.

The plastered straw bale walls (both the lime-cement prefab walls and the clay-plastered site-baled walls) are examples of permeable walls. The plasters on the interior and exterior as well as the straw insulation are very capable of allowing the movement of moisture through the materials in either direction. In this way, problems arising from moisture accumulation are prevented, and the walls have an ability to dry out in either direction should there be times of high moisture loading.

Canada’s Greenest Home also incorporates some double stud frame wall sections, including the entire south wall and the window openings in the prefab bale walls. Since we are not using plasters on these walls (we could have… but wanted to demonstrate some more sustainable, conventional approaches), a sheet barrier of some kind is required. We definitely didn’t want to give up on a vapour permeable strategy…

The south frame walls are sheathed in DensGlass for its high vapour permeability.

Ethical sourcing is part of the decision making process, so union-made materials from regional suppliers are favoured.

Our first step was to choose an exterior sheathing that is quite permeable. For this we used DensGlass, a gypsum board product (union made in Ontario, Canada and fully recycleable) with a high perm rating. Should we have moisture movement through these walls, it will be able to dry through the DensGlass at a rate similar to our plastered walls.

The second step was to find a sheet barrier that meets the current code requirements for a vapour barrier (BuildingScience.com argues for the term “vapour control layer” which is a much more accurate term for what’s required) and yet doesn’t completely blow our desire for vapour permeability.

The “smart” barrier we chose is MemBrain.

The answer seems to have come in the form of a “smart” vapour barrier, as suggested by Ross Elliott at HomeSol Building Solutions (our excellent energy auditor/advisor). In our case, we used a product called “Membrain” (insert groan here) from CertainTeed. This product (and similar versions from other companies) offers the vapour resistance of conventional plastic sheeting, but with a composition that allows for drying back through the membrane should conditions on the backside be more humid. While it lacks the low embodied energy and friendliness of the plasters we used elsewhere, these products allow conventional builders to achieve some of the same benefits at a very low cost and without having to switch building techniques.

An interior wall with the MemBrain barrier applied over the dense packed cellulose insulation.

You can read more about these “smart” barriers and how they work at BuildingGreen.com.

While we would always make plasters and natural insulations our first choice, the combination of recycled drywall, smart membrane, dense-packed cellulose insulation and permeable sheathing is a way to embrace “permeable” thinking within a mainstream paradigm.

Canada’s Greenest Home is an attempt to blend more “radical” natural building strategies with those that can work for mainstream builders. We’d like to see houses like this one be replicated by conventional builders, as well as natural builders. While builders at each end of this spectrum may choose one strategy/material over another, we think there is value in both approaches and are trying to demonstrate both in this project.

Choosing high quality windows is a very important part of our strategy to make Canada’s Greenest Home as energy efficient as possible. There is a lot to consider when making a window purchase… here is how we went about making our decision to buy Inline windows.

The triple pane, fibreglass windows from Inline have excellent thermal properties, are good looking and well made.

First thing to consider is the material that the frame of the window is made from. Choices include wood, vinyl, aluminum and fibreglass. We chose fibreglass frames for several reasons. They are long lasting, don’t expand and contract as much as other materials, don’t offgas and have good thermal resistance. Vinyl windows weren’t even a consideration, as the PVC is a red-list material for the Living Building Challenge. The offgassing of vinyl windows has been pointed out in several studies, and the material expands and contracts considerably as temperatures change, which can strain and eventually ruin the seals in the glazing. Plus, the manufacturing of PVC is a very toxic practice. There are some very good wooden windows made from FSC certified wood, which perform as well as fibreglass windows. However, there is more maintenance to ensuring wood windows have a long lifespan that is not required with fibreglass frames.

Next up to consider is the glazing (glass) portion of the window. We chose triple glazing, meaning that there are three panes of glass, with two cavities separating the panes. This adds a considerable amount of extra thermal resistance compared to typical double glazed windows.

The US Department of Energy (DOE) defines high-performance glazing as having a heat transfer coefficient (U-value) around 0.2 (R-5). Our Inline Windows have a U-value of 0.17 (R-6). By comparison, ENERGY STAR windows must achieve a U-value of 0.28 or better (R-3.6). High-performance glazing also often includes spectrally selective coatings, which filter out from 40% to 70% of the heat normally transmitted through clear glass while allowing the full amount of light to be transmitted. We chose windows with different coatings on the glass for different sides of the house. On the south side, we wanted the highest solar heat gain co-efficient (SHG), while on the west we wanted to block out the sun to prevent overheating and on the north we wanted the best possible heat retention. Inline was able to provide windows for each of these scenarios.

Most windows are now manufactured to have an inert gas (usually argon) between the panes of glass to further reduce heat transmission between panes.

There is a lot of good, useful information provided by window companies right on the window (and usually in catalogues and websites). This should include the whole window U-value, solar heat gain coefficient (SHGC), visible transmission figures plus any certifications the window has earned (Energy Star, etc.).

This window has a low solar heat gain coefficient (SHGC) because it’s on the north side of the house. It has reflective coatings (low emmissivity or Low-E) that reflect heat back into the house.

This window is on the south, where we want the most solar heat gain.

A couple last issues factored into our window choice. Inline uses an insulated spacer between the panes of glass, as opposed to many companies that use metal spacers which conduct a lot of heat across the edge of the entire glazed surface. Inline also makes “thermally broken” frames, which means that the frame is not continuous from the inside of the window to the outside, further improving whole window thermal performance.

We also chose casement and awning windows because they can achieve much tighter seals than horizontal or vertical sliders.

Finally, Inline offers a wide range of styles and we were able to pick a frame colour and trim shape that worked with our aesthetics and our siding choices.

It is worth doing lots of research before purchasing windows. This is one area where you usually get what you pay for… and where quality and performance make a big difference in the energy efficiency of the building.

There is good information about making window purchasing decisions at Natural Resources Canada.

The Endeavour Centre has teamed up with The Seasoned Spoon Cafe at Trent University to build a buried root cellar for the over-winter storage of vegetables grown at Trent gardens and destined for yummy dishes in the cafe.

The walls of the building are made with earthbags. In this technique, a soil mixture that has good compaction qualities (lots of different sizes of aggregate and slightly moist) is placed into long polypropylene tubes and tamped in place. Also known as “flexible form rammed earth” this technique is just about the simplest, cheapest, most sustainable and most effective building techniques we use at Endeavour. While it requires a lot of grunt labour, it is satisfying work with immediate and satisfying results.

Once the building has its roof in place, the whole thing will be buried in the ground and will become a small, wildflower covered hill on the Trent campus, very close to the Seasoned Spoon. The earthbag arch entryway will be the only visible feature of the building.

Inside, the building will have both a damp and a dry room, for the storage of different vegetables. The dry room will be separated from the ground by a vapour barrier, while the damp room will have a floor that is not sealed from the ground beneath. The two rooms will be separated by a compressed earth block wall. Both rooms will be ventilated by earth tubes, which are long pipes buried deep around the building with an inlet that draws fresh air from outside and a solar fan that provides exhaust. The air in the tubes will be cooled to earth temperature in the summer and warmed to earth temperature in the winter, providing the root cellar with a fairly constant temperature of around 10C.

We will continue to post the progress of the root cellar as it moves toward completion.

If you are interested in volunteering on the root cellar, The Seasoned Spoon is relying heavily on volunteers to help with construction. You can contact us to find out more about volunteer opportunities.