Denver Developer Focuses on Zero-Energy Homes
General Specs and Team
Location: Denver, CO
Living Space : 2115 sqf
Builder: Bill Rectanus, New Town Builders
Energy consultants:Peter Oberhammer, EnergyLogic, Inc.
Foundation: Conditioned basement with R-19 interior wall insulation
Wall construction: Double-stud 2x4 walls, advanced-framed, with 9.5 inches blown fiberglass (R-40.7)
Windows: Double-pane, low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor., vinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate).-framed, U=0.25, SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.=0.27
Roof: Vented attic framed with 14-inch raised-heel trusses
Attic insulation: R-50 blown-in fiberglass attic insulation
Air leakage rate: 2.11 ach50
HERSIndex or scoring system for energy efficiency established by the Residential Energy Services Network (RESNET) that compares a given home to a Home Energy Rating System (HERS) Reference Home based on the 2006 International Energy Conservation Code. A home matching the reference home has a HERS Index of 100. The lower a home’s HERS Index, the more energy efficient it is. A typical existing home has a HERS Index of 130; a net zero energy home has a HERS Index of 0. Older versions of the HERS index were based on a scale that was largely just the opposite in structure--a HERS rating of 100 represented a net zero energy home, while the reference home had a score of 80. There are issues that complicate converting old to new or new to old scores, but the basic formula is: New HERS index = (100 - Old HERS score) * 5. Index: 38 without PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow.; -3 with an 8-kW PV system
Estimated annual energy use: $1,414 without PV, $5 with PV
Actual annual energy use: Unknown
PV arrays are an available option
Space heat and cooling: Air-source heat pumpHeat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps., 12.7 HSPF, 19.8 SEER(SEER) The efficiency of central air conditioners is rated by the Seasonal Energy Efficiency Ratio. The higher the SEER rating of a unit, the more energy efficient it is. The SEER rating is Btu of cooling output during a typical hot season divided by the total electric energy in watt-hours to run the unit. For residential air conditioners, the federal minimum is 13 SEER. For an Energy Star unit, 14 SEER. Manufacturers sell 18-20 SEER units, but they are expensive. , with forced-air ductwork for distribution; 97.3 AFUEAnnual Fuel Utilization Efficiency. Widely-used measure of the fuel efficiency of a heating system that accounts for start-up, cool-down, and other operating losses that occur during real-life operation. AFUE is always lower than combustion efficiency. Furnaces sold in the United States must have a minimum AFUE of 78%. High ratings indicate more efficient equipment. gas furnace for backup.
Ventilation: Exhaust-only 15-watt fan rated at 71 cfm
Domestic hot water: 0.947 EF(EF). Efficiency measure for rating the energy performance of dishwashers, clothes washers, water heaters, and certain other appliances. The higher the energy factor, the greater the efficiency. In some appliances EF reflects the percentage of energy going into the appliance that is turned into useful energy. tankless gas water heater
Lighting: 100% CFLCompact fluorescent lamp. Fluorescent lightbulb in which the tube is folded or twisted into a spiral to concentrate the light output. CFLs are typically three to four times as efficient as incandescent lightbulbs, and last eight to ten times as long. CFLs combine the efficiency of fluorescent light with the convenience of an Edison or screw-in base, and new types have been developed that better mimic the light quality of incandescents. Not all CFLs can be dimmed, and frequent on-off cycling can shorten their life. Concerns have been raised over the mercury content of CFLs, and though they have been deemed safe, proper recycling and disposal is encouraged.
Appliances: All Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners.
WaterSenseProgram developed and administered by the U.S. Environmental Protection Agency to promote and label water-efficient plumbing fixtures. compliant fixtures
"Smart" recirculation pump that learns occupants' behavior
Green Materials and Resource Efficiency
Beetle-kill lumber used for all framing lumber
Roadways, bridges, and bike paths use recycled concrete
DOE Zero Energy Ready
DOE Energy Star
EPA Indoor airPLUS
Double-stud walls effectively reduce thermal bridging
A Denver-area developer, New Town Builders, is aiming to make all of its new homes zero-energy-ready by the end of 2015.
“Our goal is to be 100% U.S. Department of Energy (DOEUnited States Department of Energy.) Zero Energy Ready certified on all of our single-family homes,” said Bill Rectanus, vice president of New Town Builders, which plans to build 150 single-family homes in the Denver metro area in 2015.
The builder constructed its first home to DOE’s Zero Energy Ready Home program criteria in 2013 and has been gradually moving toward certification across the board since then. New Town was in the process of building 29 homes in its Solaris community when it learned about the DOE program. Most of the 29 homes in the first phase of Solaris are certified and all 34 homes in the next phase of Solaris will be certified. (To read a 2013 GBAGreenBuildingAdvisor.com news story on New Town Builders, see Denver Builder Embraces ‘Challenge Home’ Standard.)
All of the homes come with a roof-mounted photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. (PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow.) system rated at 2.75 kW or more. In Phase 2, New Town's goal is to install 5-kW systems. Home buyers will have the option to add more PV to achieve a true net-zero-energy home — that is, a home that produces as much power as it uses in a year.
The entire development aims for zero energy
In New Town’s Z.E.N. (Zero Energy Now) community, which has 30 homes at or near completion and 33 more homes planned, all of the homes are true zero-energy homes. New Town is in the planning stages on two additional projects: Hyland Village, a development of 75 single-family detached homes, and Perrin’s Row, a development of 26 attached homes. Both communities will be 100% DOE Zero Energy Ready.
To be certified as a DOE Zero Energy Ready Home, a builder must meet the requirements of Energy Star HomesA U.S. Environmental Protection Agency (EPA) program to promote the construction of new homes that are at least 15% more energy-efficient than homes that minimally comply with the 2004 International Residential Code. Energy Star Home requirements vary by climate. Version 3.0, the U.S. Environmental Protection Agency’s Indoor airPLUS and WaterSenseProgram developed and administered by the U.S. Environmental Protection Agency to promote and label water-efficient plumbing fixtures. programs, and the insulation requirements of the 2012 International Energy Conservation Code. In addition, DOE Zero Energy Ready certified homes must locate all ducts in the conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. , meet higher window criteria, and have renewable energy equipment or “renewable-ready” measures installed that ensure that the home is ready for a PV system and a solar thermal system when the homeowner is ready to purchase them.
Double-stud walls and advanced framing techniques
One of New Town's models, the ArtiZEN, provides a good example of how the builder achieves the DOE Zero Energy Ready Home certification. The home is built with double-stud walls consisting of two 2x4 framed walls separated by a 2 1/2 inch gap. After the exterior wall is sheathed with OSB, netting is stapled to the inside edge of the inner wall studs, creating a 9.5-inch-deep wall cavity that is filled with blown-in fiberglass insulation. Because the insulation runs as a continuous layer through the wall, thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. is limited.
Advanced framing techniques were employed on both walls to reduce the amount of lumber used and to leave more room for insulation. These techniques included using single rather than double top and bottom plates, 2-stud rather than 3-stud corners, 24-inch-on-center rather than 16-inch-on-center stud spacing, insulated rather than solid wood headers over windows, and ladder blocking at interior-exterior wall intersections.
The attic is constructed with 14-inch-high raised heel “energy trusses” to ensure plenty of space for insulation at the eaves, just above the outer walls. A full R-50 of blown-in fiberglass insulation blankets the floor of the vented attic. The basement walls are insulated on the interior to R-19.
New Town paid extra attention to air sealing measures. Spray foam was used to seal around windows, behind outlets, at bottom plates, and at any holes for wiring or plumbing. Workers also applied a bead of pliable sealant product along the top plates of all walls bordering the attic and the garage before installing drywall. This nonhardening sealant spreads out when the drywall is screwed in place, forming an airtight gasket.
On the second floor, any exhaust fans, can lights, etc., that might typically be installed in the ceiling were installed in dropped soffits below the ceiling drywall instead so that the ceiling drywall, which serves as the primary air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. separating the house from the attic, could be kept intact and hole-free.
Blower door testing of the home showed air leakage of 2.11 air changes per hour at 50 Pascals pressure difference (ACH 50) between the inside and outside — making the homes tighter than many new homes, but not tight enough to meet the PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. standard.
Materials and systems picked for efficiency
All of the home’s windows are double-pane, vinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate). framed, with low-emissivityAmount of heat radiation emitted from a particular body or material. Emissivity is expressed in a fraction or ratio, with the lowest values indicating low emissivity and the highest indicating the high emissivity of flat black surfaces. coatings to reduce heat transfer. The windows are rated at U-0.25 and have a solar heat gain coefficient(SHGC) The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. (SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.) of 0.27. Generous roof overhangs minimize summer solar heat gain.
The home’s heating system consists of a ducted heat pumpHeating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump. with a heating efficiency of 12.7 HSPF and a cooling efficiency of 19.8 SEER(SEER) The efficiency of central air conditioners is rated by the Seasonal Energy Efficiency Ratio. The higher the SEER rating of a unit, the more energy efficient it is. The SEER rating is Btu of cooling output during a typical hot season divided by the total electric energy in watt-hours to run the unit. For residential air conditioners, the federal minimum is 13 SEER. For an Energy Star unit, 14 SEER. Manufacturers sell 18-20 SEER units, but they are expensive.
, above the minimum federal standards of 7.7 HSPF and 13 SEERSeasonal Energy Efficiency Ratio (SEER) is the total cooling output (in BTU) of an air conditioner or heat pump during its normal annual usage period divided by its total energy input (in Watt-hours) during the same period. The units of SEER are Btu/W·h. SEER measures how efficiently a residential central cooling system operates over an entire cooling season. The relationship between SEER and EER depends on location, because equipment performance varies with climate factors like air temperature and humidity.. On the rare days when the temperature drops below 5°F, a high-efficiency gas furnace is
available to kick in.
A tankless water heater with an energy efficiency factor of 0.947 provides domestic hot water. The home has a “smart” recirculating system that learns the occupants’ behavior and initiates the pump at times of high use throughout the day.
A drip irrigation system minimizes water use outside. All of the home’s lighting uses energy-efficient compact fluorescent lamps and all of the appliances are Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. rated.
The 2,115 square foot, three-bedroom, 2.5-bath, two-story home achieves a Home Energy Rating System (HERSIndex or scoring system for energy efficiency established by the Residential Energy Services Network (RESNET) that compares a given home to a Home Energy Rating System (HERS) Reference Home based on the 2006 International Energy Conservation Code. A home matching the reference home has a HERS Index of 100. The lower a home’s HERS Index, the more energy efficient it is. A typical existing home has a HERS Index of 130; a net zero energy home has a HERS Index of 0. Older versions of the HERS index were based on a scale that was largely just the opposite in structure--a HERS rating of 100 represented a net zero energy home, while the reference home had a score of 80. There are issues that complicate converting old to new or new to old scores, but the basic formula is: New HERS index = (100 - Old HERS score) * 5.) score of 38 without counting the PV array and would save its homeowners about $493 in energy bills compared to a home built to the 2009 IECC International Energy Conservation Code..
When 8.0 kW of PV panels are added to the roof, the home achieves a HERS score of -3 and saves its homeowners a whopping $1,902. For comparison, a home built to the 2009 IEEC code would score about a HERS 85.
The home also meets all of the healthy indoor air requirements of the EPA’s Indoor airPLUS program, including moisture-management measures, ventilation requirements, and low- or no-VOCVolatile organic compound. An organic compound that evaporates readily into the atmosphere; as defined by the U.S. Environmental Protection Agency, VOCs are organic compounds that volatize and then become involved in photochemical smog production. criteria.
Community and infrastructure embraces recycling
The home is a poster child for the green slogan “recycle, reuse, reduce,” starting with its location in the Stapleton area of Denver. Once home of the old Denver International Airport, the 6,500-acre site has been recycled into a planned community of schools, shopping, and over 8,000 homes. Developers have crushed over 6 million tons of runway concrete to reuse as roadways, bridges, and bike paths.
The eight home builders at Stapleton have committed to meeting at least ENERGY STAR 3.0 certification, which means their homes will reduce energy use at least 30% compared to a typical new home in Denver. New Town’s homes will reduce energy use by 85% compared to typical homes.
New Town Builders has gone further, committing to framing all of its homes with Colorado beetle-kill lumber, which is wood harvested from trees that have been killed by beetles, leaving a blue fungus that stains the wood. “It’s actually a great framing material because it’s been dried in the Colorado sun before going to a local mill for cutting, so it stays very straight and true after installation,” said Rectanus.
New Town Builders works closely with all its trade partners to negotiate fair prices with partners while keeping home costs competitive for homebuyers. To help its subcontractors, New Town provides detailed scopes of work and project specifications. Energy-efficiency details are included on each plan set and New Town is committed to providing continued training to its staff and trade partners. Every home also receives two third-party inspections — from the energy rater and from an additional construction quality assurance company.
“Building to DOE’s Zero Energy Ready Home certification drives us to pay attention to the details that enable us to provide a more durable, high-quality home. Moving forward, New Town is positioning itself as the area’s leading zero energy home builder.
“100% compliance with the DOE Zero Energy Ready Home program helps us to achieve that consistency across all of our projects and product types. We appreciate the third-party validation that comes from partnering with DOE,” said Rectanus.
Courtesy U.S. Department of Energy
- New Town Builders
Jun 3, 2015 11:04 AM ET