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Among the many challenges involved in meeting the Living Building Challenge standard for Canada’s Greenest Home, one of the biggest was how to heat the home given that the LBC does not accept combustion devices of any kind for any purpose.
Our first choice for heating this home was going to be a pellet boiler. Impressed with the efficiency and cost of these systems, we were also aware that a number of local pellet making facilities (including one less than 1km away from the home) meant that our fuel supply could be reliable and entirely based on existing waste biomass in the region.
Once we understood that this combustion option was not feasible (and I’m not sure I agree with the LBC’s reasoning on this point), our focus turned to heat pumps, both ground source and air source. Heat pump technology is a great option, as it is the only heating (and cooling) technology that is more than 100% efficient. With combustion devices, for every unit of fuel input there is slightly less than one unit of heat output (hence the ratings that might state efficiencies in the 90% range). With heat pumps, each unit of energy input (electrical energy, used to drive the pump) there is between 1.5 and 5 units of heat created, meaning that efficiencies can be stated in the 150-500% range.
A heat pump works by circulating a refrigerant with a boiling point that is designed to be in the temperature range expected on the outside of the building. By compressing this gas and forcing it into a gaseous state and then allowing it to return to a liquid state, the refrigerant goes through two phase changes. The heat that is transferred during these phase changes is significant, even though the temperature of the refrigerant is not.
This isn’t magic, and it isn’t even a new technology. Your refrigerator is a heat pump, as is your air conditioner. The premise has been around for decades, but has only recently been applied to heating homes on a large scale in the past decade. The use of heat pumps in cold climates has not been feasible until quite recently, when Mitsubishi introduced their Zuba range of cold climate heat pumps. These units are able to make usable heat at temperatures as low as -30C, making them feasible as the sole heat source for a northern climate home as long as the home is made to be energy efficient.
The heat loss calculation for Canada’s Greenest Home was 22,524 Btuh (British Thermal Units per hour). The Zuba is capable of producing 34,130 Btuh, so it is well within the unit’s capacity to fully heat this home.
As with all heat pumps, the Zuba can run in reverse and be an efficient air conditioning unit in the summertime.
The Zuba has two components. On the exterior of the house there is the heat pump unit. On the interior of the house there is the heat exchanger and the air plenum plus the fan and switchwork for the system. It is connected to conventional ductwork to supply heated air to the whole house.
The Mitsubishi Zuba units are supplied in Ontario by Mitsair. Our system was installed by Crown Heating in Peterborough. Our thanks to both companies for their professional assistance.
The decision to go with an air source heat pump was made largely based on the cost of installation. While a ground source unit offers better efficiencies (especially at colder outdoor temperatures), the cost of installation is quite a bit higher, and the payback on the additional investment is well over a decade. Given our investment in other technologies for this home, we decided in this case that the lower cost of installation and the very good efficiencies for the unit made it the right decision for Canada’s Greenest Home.
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.
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 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.
High among the priorities for Canada’s Greenest Home is the attempt to make the house a net zero energy building. To reach this goal, we began by designing the most efficient home we possibly could, making energy reduction a major factor in every decision we made during the design and construction process. But this house will use energy, and to offset its consumption we have installed a 5 kilowatt photovoltaic (PV, or “solar panel”) system on the roof. These panels generate electrical power that should, over the course of a year, equal the annual energy consumption of the building.
Sean Flanagan and the excellent team at Flanagan and Sun came and installed the system on our roof this past week. It was exciting to have our first mechanical installation done. PV installations are quite straightforward and fast compared to many mechanical systems. The racking, panels and inverter were all put together in a couple days.
Here in Ontario, the MicroFIT program is run by the provincial government to encourage the addition of small scale renewable energy sources to the overall electricity grid. Homeowners can apply for a MicroFIT contract for systems under 10 kilowatts of peak production power. The government guarantees a sale rate for all such generated electricity for a 20 year contract. The program has been very successful in creating a lot of renewable energy on the grid and helping to reduce costs for system components by making it an attractive investment.
People in Ontario may have heard that the MicroFIT rates were recently reduced from 80 cents per kilowatt hour to 54.9 cents. While this may seem like a disincentive to pursue a MicroFIT contract, in reality the rate reflects the fact that the program’s success has brought down the price of a PV system so dramatically that the rate of return on a system today is similar to that under the higher rate a few years ago. For Canada’s Greenest Home, a MicroFIT contract is an excellent way to meet our net zero targets and create a home which actually pays the owner (around $4,000 annually) while erasing all utility bills. We compare the PV system to building a rental apartment in the house, except that the tenant is completely quiet, always pays up on time and doesn’t add any wear and tear to the house or the owners!
The MicroFIT program in Ontario is one of the best renewable energy incentive programs in the world, and a bright spot in an otherwise dismal landscape for government support of sustainable housing. Seeing the panels on our roof is a point of pride and a look at what all houses could be doing in the future.
Instructor Name: Chris Magwood
Solar hot air collection is the easiest and most cost effective do-it-yourself use of solar energy to help heat your home, garage, workshop or greenhouse.
Solar hot air panels can be made from readily available recycled materials and mounted on any south-facing wall or window. The panels we will make in this workshop feature an effective collection box, PV driven fan, anti-thermosyphon air intakes and a simple shut-off mechanism. Not only do these panels provide free heating energy, but they also provide fresh air intake during the winter months.
Each participant will build his or her own collector to take home at the end of the workshop. Come and get a start on making your own solar heat this winter!
Open to all
$300, (includes $100 material fee)