Net-Zero Energy Homes

Definition of a Net-zero Energy Home A Net-zero Energy Home (NZEH) is “capable of producing, at minimum, an annual output of renewable energy that is equal to the total amount of its annual consumed/ purchased energy from energy utilities” and emits zero net carbon (1). This concept is becoming increasingly popular as people are becoming more aware of the effects of buildings on the environment. However, to build a net-zero home, in-depth design considerations to minimize “the energy requirements for space heating, cooling and water heating” are required (2).
This will result in the least amount of artificial ighting, heating, and air conditioning to be used to achieve human comfort level (2). Designing for Building Orientation The best building orientation for making efficient use of solar energy is south. Thus, running the buildings long axis from east to west and facing within 30 degrees of due south is strongly recommended (Figure 1). This allows the house to receive at least 90 percent of the optimal winter solar heat gain. The buildings south orientation should also be clear from obstacles to allow unblocked sunlight to enter the house (3).
Use and Placement of Windows Windows let in sunlight but trap long-wave radiation, making the indoor temperature rise; however, in the absence of sunlight, windows let out considerable amount of heated air due to their high conductivity. To minimize this effect, selecting windows with special coatings are recommended. Window sizes have to be determined carefully because of these unique properties, to balance heat loss and heat gain: Net window area should be at least five percent of net floor area with each room or space having one or more windows.

Glare can often become problematic especially through south-facing windows but this can be prevented by using low-emissivity oated windows. Sloped or horizontal windows such as skylights must be used with caution because they can become major areas of uncontrollable heat loss, overheating, and condensation (3). Controlling Airtightness Holes, cracks, floors, walls, ceilings, roofs, and outlets are all susceptible locations of air leakage. Air leakage equals energy leakage because as heated air leaks out of the building, the cooler air outside tends to get sucked into the building.
Therefore, tight sealants around all Joints and openings are required. Proper Insulating Techniques An NZEH should also be well insulated around the building envelope to minimize eat transfer. This is achieved by using proper installation of insulation that meets the required R-value (Figure 2). This will not only minimize the energy loss but also reduce the need for supplementary heating (3). Providing Ventilation by Mechanical or Natural Systems Ventilation can either be mechanically or naturally provided.
Before energy conservation became an issue to building occupants and the construction industry, buildings were not as airtight as they are today and natural ventilation was sufficient. Building occupants could open and close windows for fresh air and continuous entilation was always present through the building’s cracks and openings. In airtight buildings, natural ventilation is unreliable because buildings have fewer openings and cracks for natural air flow and the weather is often too cold or rainy for occupants to leave windows open for maintaining adequate relative humidity and fresh air circulation (4).
One of the mechanical ventilation systems is the exhaust-only system, which exhausts air out of the building through an exhaust fan (Figure 3). This can be cost effective and functional provided that the building is airtight enough to run this system. If the building has cracks that act as an air path, the air that gets exhausted out can get sucked back into the building, essentially defeating the purpose of the system. Also, in humid climates, the exhaust-only system tends to cause condensation problems in wall cavities (4).
Supply-only ventilation provides fresh air through vents and is extremely effective in providing high indoor air quality when the system is designed and installed according to the building size and specifications. This system can also be combined with a heating system or a humidifying system to suit the occupants’ needs. This system makes the indoor air pressure higher than the outdoor air pressure, which can work to the occupants’ advantage if the building is located in hot and humid climates because the positive air pressure will resist the hot and humid pressure from getting sucked into the building.
However, this is problematic in cold climates because hot and moist indoor air will push against the warm side of the wall cavities, which leads to condensation problems (5). An exhaust and supply balanced system is the most ideal system as it can serve all climates. Increasing the Efficiency of Furnace and Air Conditioner Systems Two of the major sources of energy consumption in todays households are the furnace in the winter and the air conditioner (A/C) in the summer. Increasing the quality and efficiency of the furnace and A/C will make some of the greatest returns in cost.
Three main factors contribute to healthy and efficient furnace and A/C systems: Correct installation by qualified trades. Properly sealed supply and return duct system with approved tapes or mastics to minimize air loss. Continued maintenance throughout the lifetime of the furnace and A/C. Where space and cost conditions permit, consider ground-source heat pump echnology as opposed to ENERGY [email protected] furnaces: “A ground-source heat pump uses the earth or ground water or both as the sources of heat in the winter, and as the “sink” for heat removed from the home in the summer.
For this reason, ground- source heat pump systems have come to be known as earth-energy systems (EESs). Heat is removed from the earth through a liquid, such as ground water or an antifreeze solution, upgraded by the heat pump, and transferred to indoor air. During summer months, the process is reversed: heat is extracted from indoor air and transferred to the earth through the ground water or antifreeze solution. A direct-expansion (DX) earth-energy system uses refrigerant in the ground-heat exchanger instead of an antifreeze solution” (6). Figure : Schematic Diagram of a Ground-source Heat Pump Source: http://www. ge04va. vt. edu/A3/A3. tm Water Conservation Techniques through Efficient Water Distribution Systems After heating and cooling, water heating is typically the next largest energy user ot the home because it is necessary for so many domestic activities. Heating water is a large cost especially if a home has out-dated appliances. These next tips can substantially reduce energy consumption simply from water conservation based eating systems. Firstly, a tank less on-demand water heater is advantageous for residences already conserving water, for hot water users relatively close together, and for communities living where natural gas is readily available (Figure 5).
Secondly, consider a solar hot water pre-heat system with a parallel piping system for the hot water outlets. Solar energy is the most economical and available energy source and should be utilized to its full potential. The key is to have a knowledgeable solar hot water instillation company perform the installation so proper instillation is achieved. Finally, another cost-effective method to conserve water usage is to install low-flow fixtures. Thousands of gallons of water are wasted everyday because of unnecessary use from high-flow fixtures. Figure : The Process of a tank less water heater Source: http://kerrygoldplumbing. om/tankless-gas-water-heaters Energy Efficient Lighting Fixtures and Lighting Energy efficient lighting fixtures, lighting, and energy efficient appliances meet a standard of reduced energy use rated by ENERGY STARL Such appliances consume significantly less energy and water than the standard products. Energy efficient ighting fixtures use about 25% the amount of energy of a regular incandescent light fixture (7). Such fixtures are specifically made to work with fluorescent or LED lights and therefore use less energy. Fluorescent light bulbs consist of a gas-filled tube and magnetic or electronic ballast (8).
These bulbs last about 10 times longer (9 years at 3 hours/day) and run cooler than a standard incandescent light bulb (8). Light-emitting diode (LED) lighting consists of a semiconductor diode that converts applied voltage to light (9). LED lighting is available in many different colors and izes, has a lifetime of more than 22 years but still very expensive. Energy Efficient Appliances Energy efficient appliances are rated by ENERGY [email protected] and use 10 to 50 percent less energy and water than standard models because these products use advanced technology in their systems (10).
These appliances are readily available and can be found at all appliance retailers such as Future Shop, Best Buy and Sears. Photovoltaic (PV) systems Photovoltaic (PV) systems are comprised of solar cells which convert sunlight directly into electricity (11). These cells or semiconductor wafers, installed on the sun-facing ide of buildings, are protected from rain, hail and other inclement weather elements by a glass sheet (11). As photons from the sunlight knock electrons into an excited higher energy state, electricity is created and captured by the solar cells (11).
These solar cells are connected in either series or parallel or both to form PV modules, and in applications the PV modules are arranged in arrays. PV systems produce D power and electricity fed into the electricity grid is converted by inverters to AC power. Current PVsystems in use have a 12 to 18 percent average efficiency in converting sunlight to electricity (11). Current developments have achieved an efficiency of 42 percent (11). Residential Applications for PV Systems In residential building, PVsystems are typically installed on roofs or on walls.
Roof tiles with integrated PV cells can also be purchased. The use of the residential PV system allows the home to be connected to the electricity grid and surplus power deposited into the grid. To acquire a net-zero energy balance, the goal is to produce as much power from PV systems as you consume from the power grid, so that at the end of the year the homeowner pays absolutely nothing for power. The upfront cost f current PV systems is still relatively high typically costing installed (12).
Working Towards a Canadian NZEH Building Standard Although there is currently no Canadian net-zero energy home building code, work is progressing to lead Canada towards such a building approach. Leading the way is the Net Zero Energy Home Coalition, formed in 2004, whose mandate is to promote existing and available energy efficient and renewable energy technologies to supply residential energy in a sustainable manner in order to minimize the production of greenhouse gases and create healthier, greener communities (1).
Comprised of ome builders and developers keen in applying renewable energy resources to residential building, the Coalition in partnership with the Canada Mortgage and Housing Corporation (CMHC), Natural Resources Canada, Industry Canada, and Environment Canada, aims to establish a new Canadian NZEH building standard by 2030. To showcase the viability of NZEHs, the CMHC, supported by the Net-zero Energy Home Coalition, is currently leading a demonstration building project called the Initiative.
Fifteen teams across Canada were selected to build demonstration homes using the various techniques discussed in the previous ections. To date, six of the fifteen homes have been completed in Alberta, Ontario, and Quebec (13). Initiative NZEH Examples – New and Old The Alstonvale Net Zero House is an example of new NZEH construction while the Now House Project demonstrates how NZEH principles can be economically applied in home renovations. The Alstonvale Net Zero House The Alstonvale Net Zero House (shown on the cover) is a single-family detached house in Hudson, Qu©bec currently under construction.
It features an air-tight, well- insulated building envelope, extensive passive heating and cooling techniques hrough large south facing windows, sunscreens, and natural sources of shade (14). An air-to-water pump heating system connected to a PV system provides heated water for the in-floor radiant system and other domestic uses (Figure 9). Instead of standard landscaping, a large portion of the site will remain undisturbed and act as a natural habitat tor the local wildlite (14). The Now House Demonstration The Now House Project is a retrofit of a 60-year old home in Toronto, Ontario.
The project goal was “to demonstrate how home owners and contractors can dramatically mprove the energy efficiency of existing homes with a few relatively simple modifications” (15). Energy requirements were reduced by upgrading the insulation, installing low-e, argon-filled windows and energy efficient ENERGY [email protected] appliances, and replacing incandescent lighting with LED lighting (16). Increased energy efficiency and renewable energy production were accomplished through installation of solar hot water panels, a photovoltaic array, and a waste water heat recovery system (16).
Figure : A Comparison of Energy Consumption between the Now House and Average Canadian Homes Source: http://www. mhc-schl. gc. ca/en/inpr/su/eqho/noho/ upload/Now-House_E-Oct30. pdf Figure 10 on page 8 compares energy consumption rates between the average Canadian home and the Now House w. Taking into account space heating, water heating, major appliances, interior lighting and space cooling, the Now House will consume only 38 percent as much energy as an average Canadian home (16). From this demonstration, the project shows that NZEH principles are economically viable for renovating similarly older homes across the country.

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