Zero Energy Homes, convenient
How's that for a challenge? Create a zero-net energy source (as opposed to site energy consultancy in contrast) at home, and with the Department of Energy's Building America program defined. Planning for the extremes of the operating system unpredictable weather in Denver, with off-the-shelf, readily available technologies. Maintain mechanical systems more simple and easy as possible. Incorporate energy efficiency strategies that are not homeowners to become experts in sustainable building operations orPerform any maintenance on a house "normal" is required.
Not too difficult, you might say? Add that the project should be replicated for future Habitat for Humanity homes, the use of low-cost building materials and volunteer-friendly construction techniques allow. Still with me? The trick: The target market is affordable housing. Impossible, you say maybe? Difficult yes, but not impossible for an integrated design team of engineers NREL and Habitat forHumanity staff and volunteers. The finished product is 1,200 square feet, three bedroom home less income, which actually produces more energy than it consumes source!
Design Considerations
The combination of energy engineers, project managers helped a real estate and development manager of Habitat volunteers to design a balance between the ideals of the engineering modeling of energy, the reality of the costs of affordable housing and considerations involved in aVolunteer construction crew.
Volunteer work for the benefit of habitat led the design team is approaching the cost of materials at low and high cost of labor helps. While this approach reduces the cost of considerable work, when combined with the requirement for affordable housing, limits the choice of sustainable strategies. For example, strategies such as structured insulated panels (SIPs) and insulated concrete forms were not included because of their high cost. In addition, thePrerequisite for the volunteer-friendly design and simple replication eliminates the possibility of straw bales. The simplicity of the design requirement eliminates the possibility of a combined solar space heating and hot water. Finally, the zero energy requirement, since the cold weather in Denver and the high cost of photovoltaic systems, some compromises that look at some "purists" is challenged may be required.
Design Approach - Cover
Given the considerationsdescribed above, the design team decided to focus first on reducing home energy burden as possible, and then the size of the photovoltaic system to meet the residual demand for electricity. The first sight? Yes, you guessed -. A passive solar orientation with a "super-insulated" envelope From a standard three-bedroom Habitat, 26 x 46 square with a vine design, the team has increased the south side of the glass surface and reduces the north, east and The west front of the glass surface.Next, double pivot wall construction of fiberglass batt has been chosen to take advantage of it is relatively inexpensive, volunteer-friendly construction techniques and low wage costs habitats. Blown glass installed in the attic scored an R-60 rating and scored floors, an R-30 rating. During the two-stud wall design, accessible from the external structural studs at 16 cm from OC can not be advanced framing techniques Homes LEED points, the interior studs at 24 cm distanceOC certainly satisfy the requirement. The Batts R-3 fiberglass exterior wall cavity and R-13 fills the space between the outer and inner walls and cavities of the inner wall definitely help optimize energy efficiency. An outer coating permeable and fiber cement house, and carries an inner barrier and a pole steam drywall very "close" on the whole body flush R-value. Blower tests revealed a natural rate infiltration of 0.15 ACH result, very 'close'Indication.
Heating and ventilation
With home heating energy requirement is reduced drastically by this super-insulated building envelope, the design team then focused on the heating and ventilation. Note that you do not mention heating, cooling and ventilation system. Another design challenge! Habitat for Humanity Metro Denver has a policy not to equip their homes with air conditioning. This meant that the final design for the heating of reduction (for example, maximizing the maximization hadSunlight), without loading the cold.
To provide the right amount of fresh air in the house, minimizing the loss of potential energy, the team opted for an energy recovery ventilation (ERV) with efficient electronically commutated motors. This system blows air from the kitchen and bathroom, and provides fresh air into the bedroom and living room. The heat loss from respiration CAO reduced because the system heats the incoming air with heat from exhaust gasesAir.
The design team soon discovered that a very low heat load is a double edged sword. Necessary to produce little energy to heat your home. On the other hand, the most common heating systems, heating systems for such low oversized and too complicated or too expensive can not economically justified. After careful consideration of a variety of high-efficiency heating systems and much internal debate, the team decided to follow a hybrid approach to powerby the photovoltaic system and natural gas.
Controversial approach
Some of us who are "purists" are able to turn his nose at the thought of a zero-energy home with natural gas. However, the economy was convinced the design team that a hybrid approach was the best solution (see box)
The photovoltaic system on the part of the design team chose the local supply network used for storage, thus increasing the cost of substantial battery. If the system produces more energy thanis used, provides power to the grid. If the system produces less energy than it produces, it uses power from the grid.
If the system is powered from the network, it is likely the design of electricity generated with fossil fuels. Although a large-scale PV system can minimize the amount of electricity drawn from the network, the costs are prohibitive for larger systems. The design team opted for natural gas to reduce the size of a PV system of 1.1 kW, so thatThanks to favorable habitat for a home. The team developed the system to compensate for natural gas and then reached and even exceeded the goal of net zero energy source.
The hybrid approach allows the team to size the PV system that is affordable, as the use of natural gas, and all the electricity generated network, meaning that you can reach the house (and exceed) the scope of Zero net energy source. The hybrid system combines a point source heating Direct-VentNatural gas stove in the dining room and living room, with small baseboard electric resistance heaters in the bedrooms.
Hot water
The design team chose a solar water heating - instead of a combined space / water auditory system - ensured the simplicity of a natural gas water heater. The team has calculated that it would be 96 and 200 square meters of collector of liters of water in storage result annual savings of solar fraction of 88%. He chose the tanklessBack to the stove to natural gas after finding that the tankless system uses zero energy when the solar water tank at or above 115 degrees the temperature of the water supply.
The crowning element of
After all the energy loads reduced to zero as possible, the design team for lighting, appliances and other electrical equipment (Mel). They installed compact fluorescent bulbs throughout the house, and the ENERGY STAR label devices. This left the otherelectrical loads placed on television, hair dryers, toasters, computers and anything else that could be from the residents. America through integrated benchmark assumptions of Mel, the team opted for a 4 kW photovoltaic system. Since the assumptions built America on a national average of a "typical" based
American families, the actual occupants and the local climate can be used to achieve both isolated from the zero energy home, or push them into the ranks of the "net energy producer."
TheVerdict
Initial tests were encouraging. From February to July 2006, the PV system produces energy 1600 kWh more than the house. Factoring in the natural gas for heating and hot water use backup, the house produces 75% more energy than it consumes source. Although a trial period longer than is necessary, it is a safe bet to say that the house is an annual net energy producer, rather than to achieve net zero energy user. However, this couldchange if the occupants began loading more than the average in the benchmark built America.
And the house? It 'true that the house is a net energy producer, which unfortunately are not free from electric bills. And 'the monthly fee for natural gas, as well as fixed costs for electricity and gas connection fees. From October 2005 to May 2006, the owners shelled out an average of $ 18.25 per month in energy bills. Since thefixed monthly average of 80% of the invoices used in the royal household on average $ 14.60 worth of energy.
For those of us has suffered, for $ 200 + monthly electric bill for the same period, the results are very interesting.
Key features sustainable RESIDENTIAL
Energy and Environment
Passive solar design
o The house was designed with a raised glass surface along the south side and reduced glass area to the north, east and westPages.
Renewable energy
or delete 4kW photovoltaic system with storage grid, if necessary, and the associated high cost, battery
Isolation
Major or heel trusses allow 2 ft in attic insulation blown fiberglass for R-60 rating for the top thermal envelope
Floors R-30 or isolated
or R-3 Batts Batts fiber glass exterior wall cavities 2 x 4 stud structural wall and a second inner pin 2x4 with R-13 fiberglass horizontalstud walls and vertically between the internal cavity wall
siding or fiber cement casing permeable and the house
or internal poly vapor barrier and drywall
Space Heater
or hybrid gas / electric heating, the combination of a gas stove-Vent direct source point in the living room and dining room and a small electric resistance baseboard heating the bedrooms. This combination has the added benefit of heating the area, since each device has its ownindependent thermostat.
Hot water
or production of solar hot water with 96 square meters of solar collectors and 200 liters of storage, such as heating primary water heated by natural gas, water as a back up system
Windows
or double - glass, low-emissivity glass installed in windows facing south, with U-factor of 0.3 and SHGC of 0.58. For windows on the east, west and north-facing, double - glazed low - and glass was also used, with a U value of 0.22 and SHGC value0.27. The U-factors to overcome all the windows (ENERGY STAR 20%).
Appliances
or ENERGY STAR ® appliances have been installed.
Lighting
or compact fluorescent lamps used throughout the house
Indoor Environmental Quality
Local exhaust
or Energy Recovery Ventilation (ERV) with efficient electronically commutated motors, blows air from the kitchen and bathroom, and provides fresh air into the bedroom and living room.
OutdoorsAir Ventilation
The CAO or heats the fresh air sucked from the heat of exhaust gases and therefore significantly reduces heat loss by ventilation.
Materials and resources
or advanced framing techniques: The walls are made of 2x4 stud interior wall, 24 cm OC
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