Platinum with PV: Page 2 of 4

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The LEED Platinum-positioned home with PV
Platinum with PV
The home’s south face was designed to capture direct solar gain in the winter
The home’s south face was designed to capture direct solar gain in the winter, reducing the need for supplemental space heating. A 7.02 kW awning-mounted PV system is anticipated to offset all of the home’s electricity use.
A ground-level office that doubles as a guest bedroom
The home includes a ground-level office that doubles as a guest bedroom when the sliding doors are closed.
Finish materials used in the home were carefully selected
Finish materials used in the home were carefully selected to satisfy LEED point requirements and preserve indoor air quality. Forest Stewardship Council-certified white ash paneling is used for the walls of the first level, as well as on the stair treads and veneered interior doors.
Solar-electric canopy
A deck on the third story affords sweeping views of the Flatiron Mountains. The solar-electric canopy provides electricity for the house, as well as some protection from the rain and sun.
South-facing glazing admits direct solar gain
Ample south-facing glazing admits direct solar gain, which is absorbed by the concrete floor. This heat energy, stored in the floor, is released when interior temperatures drop below the floor’s temperature.
Overhangs provide some protection from the summer sun
Overhangs provide some protection from the summer sun, although heat-blocking shades are also used.
A central mass wall forms the spine of the home
A central mass wall forms the spine of the home and also serves as a passive solar collector, radiating heat when interior temperatures drop.
A clever open-air drying rack
A clever open-air drying rack, incorporated into this cabinet, eliminates the energy used to heat-dry dishes in a dishwasher. The countertops are made of Durat, a material that contains post-consumer industrial plastic.
An exterior door from the shower opens into a private outdoor vestibule
An exterior door from the shower opens into a private outdoor vestibule, allowing an indoor/outdoor shower experience.
An exterior door from the shower opens into a private outdoor vestibule
An exterior door from the shower opens into a private outdoor vestibule, allowing an indoor/outdoor shower experience.
The home’s central staircase
With slotted steel risers, the home’s central staircase acts as a giant vertical return, feeding the return air grille on the ground level.
A heat-recovery ventilator
A heat-recovery ventilator admits a continuous source of tempered fresh air to interior rooms, helping maintain good indoor air quality.
Rooftop canopy
This rooftop canopy is enhanced by a unique building-integrated PV array that also incorporates clear glass panels. The Sanyo bifacial modules in the array harvest light energy from both sides, leading to increased energy production.
OutBack Power FLEXPowerTWO
This OutBack Power FLEXPowerTWO is a fully prewired and factory-tested dual-inverter system. It comes complete with the required DC and AC wiring boxes and breakers, inverter input/output bypass assembly, and MATE monitoring system.
Two Schneider Electric charge controllers
Two Schneider Electric charge controllers protect the battery bank from overcharge and can accept the high DC voltage (412.2 Voc) from each subarray.
The LEED Platinum-positioned home with PV
The home’s south face was designed to capture direct solar gain in the winter
A ground-level office that doubles as a guest bedroom
Finish materials used in the home were carefully selected
Solar-electric canopy
South-facing glazing admits direct solar gain
Overhangs provide some protection from the summer sun
A central mass wall forms the spine of the home
A clever open-air drying rack
An exterior door from the shower opens into a private outdoor vestibule
An exterior door from the shower opens into a private outdoor vestibule
The home’s central staircase
A heat-recovery ventilator
Rooftop canopy
OutBack Power FLEXPowerTWO
Two Schneider Electric charge controllers

Meticulous Planning for High Performance

Six years of planning, design, and construction led to a 2,302-square-foot trilevel home that uses a fraction of the energy that a conventionally constructed house in Colorado might use. With energy-efficiency measures and a 7 kW solar-electric system rooftop canopy, the all-electric home is on track to produce as much energy as it uses each year and receive LEED Platinum certification (see sidebar.)

Key to the home’s energy footprint is a passive solar design that minimizes active heating and cooling needs. The German Passivhaus standard served as a guiding force during the design process.

The home’s structural, thermal, and aesthetic spine is an exposed concrete mass wall, with all the floors and ceiling joists attaching to it. The wall bisects the floor plan in such a way that every room in the house, from top to bottom, benefits from the passive conditioning. The thermal mass absorbs heat during the day and releases it throughout the evening. Although the wall appears continuous, it actually addresses three different envelope conditions: interior only; interior/exterior; and exterior only. The two 8-inch-thick concrete faces are separated by 4 inches of insulation only in the interior/exterior portion to prevent thermal transmission. The contiguous face is also thermally broken where the roof attaches to the wall.

Wall thickness was driven by the structural requirements of the second condition (interior/exterior) more than any other consideration. Based on the glazing areas, however, it was calculated that 697 cubic feet of interior mass would be needed to adequately absorb passive solar gain. This amount is attained by the interior mass wall, and by the concrete and tile floors in the office, bedroom, and living room that receive direct solar gain.

The 9-inch-thick wood-framed walls and 12-inch roof cavities, as well as the space beneath the on-grade floor slab, contain polyisocyanurate spray-foam insulation—achieving an average wall R-value of 40 and an average roof R-value of 60. Fiberglass-framed, dual-paned Serious Materials 925 windows were selected to help maximize passive solar gain on the south side, with solar heat gain coefficients ranging from 0.35 to 0.45. The south-facing master bedroom window and southwest-facing windows and doors on the first and second floors admit solar gain, which is absorbed by the floor slab and radiated when the house’s air temperature is lower than the slab’s temperature. Though also partially shaded by an architectural overhang, the southwest windows require sun-blocking shades to minimize solar gain during the summer. The first floor’s south wall is slightly angled (at 80°), creating a sculptural angle and a tapering overhang that provides more shade as the sun gets higher in the sky.

Passive & Active Considerations

As project engineer, Corbin developed multiple energy models and analyses to determine the home’s passive solar design and optimal mechanical makeup, taking into account the local climate and the area’s abundance of sun (66% of all daylight hours are sunny and clear). An initial analysis determined that the home, as originally designed, would require supplemental cooling 11% of the year and supplemental heating 77% of the year. This ratio was a factor in several design decisions, including the glazing ratio.

As a result of the energy models, the glazing area was increased to approximately 28% of the floor area, mainly on the south side of the home—a decision that reduced the building’s heating load at the expense of increased summer cooling demand.

“There’s always a trade-off when you design a home for passive heating and cooling,” Corbin says. “The large glazing area contributes to heating the building, but during the summer, it works against you. The key is finding the right balance.”

Comments (11)

zap101's picture

Looking threw the photos again I must admit i like the home. It is not all about power. The deck under the solar array, semi private, is way cool.

zap101's picture

Hi intriguing home. The center wall is it mostly the exterior wall i'm confused after viewing the photos? with only 4" of foam does the exposed portion of the outer block wall draw heat from the interior.in a zone 5 climate? Could you explain more of the walls design double wall benefits ...

Robert Dee_2's picture

Hans,
You're right, but I think this is just a magazine error, the system won't work in the layout configuration.

I wondered if it was just my perspective so I asked someone, not involved in alternate energy, to look at the house. They were completely put off by it so I took a deeper look. First the metal roof structure is costly and there are gaps between the modules, not the most efficient layout. If they were trying to maximize power why didn't they spend the money on tracking racks? It seems to me that this is not "form follows function" at all. It looks like just the opposite.
If we are trying to showcase a design that achieves net zero, or close to it, than shouldn't we be giving the masses something within their reach. I don't think the expensive metal roof structure or the off plumb glazing do that. If anything I imagine people look at it as something that is beyond them and beyond net zero in a less exotic structure.
Rob

hans harder's picture

I'm pretty sure the wiring diagram for the pv system is incorrect. On the outback inverters, the AC IN comes from the grid and AC OUT goes to loads.

Michael Welch's picture

Yes, thanks for bringing this to our attention. The correction was missed during our proofing process and has now been fixed here. We will soon have the change made in our Acrobat electronic edition for our online subscribers.

Tom M's picture

When talking about the glazing, the statement of finding the right balance is mentioned. That, along with the wants and needs of the homeowner, is what really makes a net zero home. Designing with these needs in mind, one can figure out roughly how much and what types of energy are going to be needed. Then through multiple means, since there are multiple types of energy, those factors can be incorporated into a structure that best suits it's owner.
Going by LEEDS, one gains points based upon an installed system whether or not it is a system that benefits a homeowner in a way that they require. Get lots of points, get a good rating. Though in the end the house may not be functional for everyday living.If LEEDS had any merit in my opionion, they wouldn't need to keep revising their conditions and there would only be one standard ,since they would be the deciding factor of all that is great and would require designs to conform to their ways so all buildings are platinum.
Every house is different and should be treated as such. Sometimes calculations can be wrong and it takes time and experiment to figure out what works and where the problems lie. Some functions can be automated and some may have to be manual. Energy efficeincy is a function between the user and the machine so to rely on either independently is a mistake. So no occupied house by itself can be net zero without an operator.

Robert Dee_2's picture

"Every house is different and should be treated as such."
Yes, but I think it's more than that. The article states that they searched around for the perfect property, well aren't we missing something? Isn't it easier to harness power when there is more sources of power? Isn't land power? Don't get me wrong, I applaud the person trying to maximize his or her power on a 100 by a 100 lot but that pretty much limits it to PV and hoping for a southern facing roof.
Power is microhydro, wind, etc. and it seems to me that the 'best' location is one that includes as many forms of harness-able energy as possible.
Rob

Robert Dee_2's picture

I don't like the form of the house. The off plumb windows and walls really bother me. I think you can live net zero or even net zero plus without living out of plumb.
I'm running intertie/off grid where I sell most of my energy back and just run off grid when the power fails here several times a year.
My batteries will likely last indefinitely and once my wind and micro hydro go in I expect to be net plus, even heating in the Northeast.
I think you can do it without the radical design and extra expense of non standard windows, etc.
Rob

Adam Rude's picture

Rob,

I fully respect your opinion regarding the form of the house. However, the non-standard angles were part of its conception from the beginning, for both experiential as well as sustainable reasons. The tapering geometry is more about spatial differentiation (taller ceilings and wider spaces in the living room than the kitchen while maintaining a single great room) than passive solar strategies, though the tapering overhang does address the low late afternoon sun. Yes, of course you can build sustainably in a more traditional manner. I would argue that that is actually more common than the approach of the project, which was to demonstrate that "radical," form-driven design ideas could co-exist with net-zero standards.

Regards,
Adam

Robert Dee_2's picture

Adam, thank you for your perspective.
I could accept the philosophy behind the angularity of the house more readily if they had utilized materials more efficiently and followed basic practices for optimal results. Again, the expensive metal roof structure holding the PV modules fails to maximize the benefit of a southern exposure and an optimal mean module angle, it also has wasted space between modules. Function seems to be completely lost to form here.

Rob

Jeff Franklin's picture

This article is to be commended for the engaging writing. The opening hook was unexpected good, but even more valuable was reporting the problems with Platinum certification examples of how style and substance had some divergences. It was both a personal and technical story that delivered a lot of bang for the buck in the limited space available.

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