Rob Dumont, "On the Road to Net Zero Energy Homes in Cold Climates"
Rob Dumont, building scientist with the Saskatchewan Research Council (SRC)
Summary: Mr. Dumont shared the story of the Saskatchewan Research Council (SRC’s) journey to build a “net zero” energy home – super insulated, efficient, and producing the amount of energy it consumes. Four examples of cold climate homes were presented along with their energy saving features with an emphasis on insulation and building envelopes. The presentation included construction and energy costs and their overall energy performance. He concluded with the challenges for building net zero homes and the issues that need future research.
Mr. Dumont’s presentation “On the Road to Net Zero Energy Homes in Cold Climates: Canadian Prairie Contributions” began with a comparison of the climates in Saskatoon , Canada to Fairbanks , Alaska . Fairbanks is colder (41 below compared to 31 in Saskatoon ) and has more heating degree days (13,980 compared to 11,000 in Saskatoon .) Saskatoon also has about 50% more annual solar radiation on a horizontal surface (5.0 Gj/m2 compared to 3.3 Gj/m2 in Fairbanks .) That said, Saskatoon is still a harsh northern climate and thus comparable.
Mr. Dumont’s first example of a cold-climate low energy-use house is the Saskatchewan Conservation House, a “super insulated” home built in 1977 in Regina , Saskatchewan . This home experimented with many “firsts,” installing R60 insulation values in the attic, R-44 in walls, R-60 in basement walls and R-30 in the basement floor insulation. It has vacuum tube solar collectors on the south side with a 2,900 gallon storage tank in the basement to store heat. It has insulating shutters on south windows that come down at night, a grey water heat exchanger, and Canada ’s first air-to-air exchanger. It was built on pilings due to clay soil conditions. Clay will move around and push on standard foundation systems.
“This home was very influential in helping people to understand the benefits of having a well sealed building envelope and good ventilation,” said Mr. Dumont. The SRC learned that passive solar features work very well as space heating loads are provided on most days by solar gains and heat from lights, appliances and pumps. The house needed heat from the solar collectors for only two hours in a three day period where the temperature ranged from 15 - 32 ̊F. They learned that high insulation levels, good air tightness, and passive solar design work well together and are low maintenance. They learned that ventilation is very important. Homes need about 60 cfm (or 30 L/s) of outdoor air exchange to control moisture, carbon dioxide, volatile organic compounds (VOC) and odors. They learned that heat recovery is very important in a low energy house to keep heat costs low but that maintenance is required. Providing 60 cfm of ventilation when the air outside is -31 F (-35C) requires 2 kW of heat to compensate for heat loss in ventilation systems without heat recovery. It’s also important to use low energy lights and appliances as electricity is more expensive that energy for space heating. A mantra that evolved was insulate first, then insolate (use the sun) second. They found the exterior movable insulating shutters would rattle and shake the house in high wind situations and that moving parts fail. They also found that the vacuum tube solar panels had a number of serious problems:
·Snow would collect on the outside of the individual tubes and not melt or slide off.
·In a power outage on a sunny day, the glycol mix would boil and cause a vapor lock, effectively shutting down the collectors.
·The pressure drop through the collectors was high, requiring a high wattage pump to circulate the anti-freeze solution.
·The manufacturer stopped supporting the collectors, and then stopped making them.
Overall, Mr. Dumont advised to, “Keep it simple, passive is better than active, and remember that moving parts will eventually fail.”
The second example was Mr. Dumont’s own residence built in Saskatoon in 1992. When built, it was called “the best insulated house in the world” with an R-80 attic, R-60 walls and basement, and R-35 basement floor insulation. He used about 8 tons of cellulose insulation throughout the house. He used high performance, triple glazed, low-e, argon gas filled windows with wood framing and non-metallic spacer bars. The home is well sealed and utilizes passive solar south windows, and active solar thermal collectors with a 3,000 liter water heat storage tank. They incorporated the solar panels into the design of the house, putting them on angled overhangs that provided shade for the windows in the summer. He used small windows on the north side with shutters to give them a bigger appearance. He has an 85% efficient air to air heat exchanger using brushless DC motors, energy efficient appliances using a “green plug” device on the refrigerator and freezer that lowers the voltage by about 10 - 15%, compact florescent lights (CFL), low water use appliances and landscaping, and a detached garage to keep garage fumes from entering the house. They recently did a feasibility study to see if they could reduce annual energy consumption of the Dumont residence from 13,500 kWh per year to 5,000 kWh per year with improved energy efficient appliances, bigger south facing and smaller north facing windows and improved solar thermal collectors. Coupled with a 5kW photovoltaic system, the home could achieve a net-zero status.
The SRC learned that insulation and passive features work well but a greater passive solar gain can be achieved with bigger south facing windows and better low e coatings and gas fills. “Most windows manufactured in the United States are made for the “sun-belt” and have a low transmission of solar radiation into them since southern homes need to block passive heat from entering the home. The best northern windows in the world are made by a company in Ottawa called Thermotech. They have a high solar heat gain factor, small window frame and better low e coatings,” stated Mr. Dumont. The SRC learned that when designing a house you should always design the roof to be “solar ready” for installation of a photovoltaic system when affordable. Also energy efficient appliances are helpful.
Mr. Dumont discussed embodied energy or the energy required for resource extraction, transportation, and manufacturing to create a material. Wood buildings use about one half to one third as much embodied energy as steel or concrete buildings. Wood is about 50% carbon, almost all of which is extracted from the atmosphere. The Dumont residence used natural materials over synthetic or conventional such as cedar shakes over asphalt, wood frame windows over vinyl, wood walls over concrete, cellulose insulation over fiberglass, wood floors over carpet or vinyl, etc.
The third example was the “Factor 9” home built in 2007 in Regina , Canada and designed to use 90% less energy and 50% less water than conventional homes. Water conservation is particularly important in Regina as their water source is 400 miles away in the Rocky Mountains . The Factor 9 home uses solar thermal panels set at the mid-height of the south wall and look like windows as well as spandrel glass panels and a 2,400 L heat storage tank. They used insulated brick exterior walls. The home has a rainwater catchment system for toilets and irrigation with the rainwater stored in a plastic cistern in the basement, and extraction of cooling from 15’ deep buried pilings with a liquid pump. The home has R-80 attic, R-34.5 walls, R-50 basement walls, and R-11.4 basement floor insulation. The home uses passive solar space heating through south facing windows, and the roof is oriented for south facing photovoltaic panels. The home uses the Energy Detective, a monitoring device that lets the owner know how much energy is being used by the various appliances and equipment. The home uses energy star appliances, CFL lights; a drain water heat exchanger, an air to air heat exchanger, and a fan coil with brushless fan motor.
The fourth example is the Riverdale Net Zero Duplex currently being built in Edmonton , Alberta . This home uses double 2x4 construction with blown cellulose R-100 attic, R-56 walls, and R-24 basement floor insulation. They are using “value engineering” techniques to use less lumber than a standard 2’x 6’ wall 16 inches on center. The windows are triple or quadruple glazed windows with low e and argon gas for passive solar space heating. The home has active solar thermal for water heating and photovoltaic (PV) for electricity generation using high efficiency Sanyo panels that can capture solar radiation on both sides of the panels.
The SRC put R100 insulation in the attic because they found that this is the level needed to save the cost of one annual kW of energy comparative to the cost of producing one annual kW/h of energy with PV panels. The Duplex has energy star appliances, CFL lighting, a drain water heat exchanger, an air to air heat exchanger and a whole house electricity monitoring device. The home is projected to have a net annual energy consumption of zero due to the grid connected PV system generating enough energy in a year to compensate for purchased energy used by the house.
“Some may say that so much insulation will drive up the cost of the house. Currently homes in my area cost $150 per square foot to build. The cost of the R-100 insulation was only $2.50 per square foot, a nominal extra cost for such potential savings,” stated Mr. Dumont. He discussed the challenges and lessons learned building net-zero energy homes. Two challenges are:
1. The costs of energy efficient products and systems make the homes more expensive to build,
2. Society needs to pay the real value of carbon emissions.
The biggest lesson learned was the importance of developing an integrated design where the entire building is designed as a system and not as a group of unrelated components and that considers the building envelope as the central part of the design. When energy conservation measures are used in the building envelope, in addition to lowering fuel and energy bills, they can also reduce the capital cost of a heating system by reducing the size and complexity of the system. “In milder areas, you can build these cold climate houses and eliminate the need for a heating system even. It is more cost effective to put money into improving the building envelope that into heating systems. Insulate! Insulate! Keep it simple!” Mr. Dumont implored.
Mr. Dumont concluded with a discussion of issues needing more research:
1. Improved reliability of heat recovery ventilation systems (air-to-air heat exchangers) that have reduced maintenance requirements and reliable defrosting in cold climates. The energy costs to run some heat exchangers (50 – 200 watts of electricity) are higher than the heat energy saved, so they need energy efficiency improvements.
2. Improved efficiency refrigerators and freezers, better insulated and lower costs.
3. Reduced phantom loads from electricity leakage.
4. Integrated windows and photovoltaic systems
5. Passive solar access through street orientation for housing developments