Platinum with PV: Page 3 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

To minimize heat gain during the summer, reflective shades are installed over the south and west windows. Brigham keeps the shades drawn from noon to sunset, if not longer, between May and September.

Only electric appliances were installed, including an induction cooktop, convection oven, and two on-demand tankless water heaters (see sidebar.) Brigham opted for passive alternatives to dishwashing and clothes drying. After being hand-washed, dishes air-dry in kitchen cabinet racks, where they are also stored. In the laundry room, a large floor-to-ceiling cabinet hides drying racks for clothing. A high-efficiency lighting scheme utilizes a combination of LED and fluorescents to help minimize energy consumption and meet LEED requirements.

Domestic hot water loads were modeled at 25 gallons per day per person, within the range of typical residential loads suggested by ASHRAE. This load represented cooking, cleaning, bathing, and waste water usage, but did not include the additional water required for a large soaking tub originally designed into the master bathroom. “It was one of the few things the homeowner really wanted,” Sofield says. “But she opted not to build it after she saw the numbers.” Each bath would have used 11.75 kWh and at least 100 gallons of water—more resources than Brigham felt comfortable consuming for what she considered to be a luxury item.

Throughout the home, fixtures and fittings satisfy the LEED requirements for water-use efficiency, meeting the set limits for average flow rates—less than 1.5 gallons per minute for the faucets and outdoor spigots, less than 1.75 gpm for the showerhead, and less than 1.1 gallons per flush for each of the two toilets. A small-capacity Energy Star clothes washer handles Brigham’s weekly washing needs. Additionally, the home claimed the maximum LEED credits allowable for managing roof runoff. In Colorado, where water laws dating to the 19th century still grant usage rights to roof runoff to downstream users, rain retention is prohibited. Sofield enlisted a civil engineer to size the infiltration ponds appropriately to return water to the aquifer.

Heating & Cooling

The home’s heating, ventilation, and air-conditioning system relies on a high-efficiency Carrier electric air handler capable of delivering 1,050 cfm in cooling mode and 945 cfm in heating mode. Modeling showed that the cost of the additional PV needed to operate the air handler was less than the cost of an air-source heat pump, the primary alternative considered. 

The floor between the first and second levels houses the supply-air ductwork that provides conditioned air to all spaces. Return-air circulation occurs naturally through gaps beneath the doors into the bath and laundry rooms, and louvered doors into the first-floor office. With slotted-sheet steel risers, the staircase acts as a giant vertical return, feeding the return air grille on the ground level.

Cooling is accomplished with an earth tube (or ground-loop heat exchanger)—a 12-inch-diameter PVC pipe buried 3.5 feet deep beneath the home that runs along the perimeter of the foundation. Return air from the home circulated in the tubes is cooled by the ground temperature and delivered back to the house via the air-handler. Based on average earth temperature data from the National Renewable Energy Laboratory, the earth tube can provide air cooled to 78°F—even during the hottest months of July and August. Ideally, the earth tube, Corbin says, would have been trenched deeper into the ground to provide even cooler air, but digging deeper was cost-prohibitive.

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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