Design Factors

The design of the ICON Solar House is based on the familiar gabled roof form of an American family home. The iconic shape is welcoming and blends in with the context of a traditional neighborhood, combining unfamiliar technology with the popularly accepted iconic imagery to create a new tradition.

The ICON Solar House is a step toward the fusion of traditional style and new technology. By adjusting the geometry slightly, the gabled form is optimized for solar collection within the U.S. Department of Energy’s Solar Decathlon competition parameters.  - Solar Components are placed on the sun-drenched south side (orange) - Traditional Gable House (red)  - Traditional Solar House (green)

The Sun

Minnesota lies in the north central part of the United States, between 43°N and 49°N latitude. Summers are hot, with the sun almost directly overhead, but in winter, the sun in Minneapolis is only 54° above the horizon. This presents a challenge when designing a solar array, because in order to function, both photovoltaic (PV) panels and solar thermal panels must be aimed directly at the sun.

Changing Seasons
The low winter sun angle lets sunlight enter deep into the living space through the south side windows, improving daylighting and reducing the need for electric lighting. 
Additional solar thermal collectors on the south side of the house take advantage of this low angle.

-	Midsummer provides 16 hours of daylight
-	Midwinter provides 8 hours of daylight
On the ICON Solar House, the ridge of the roof is pulled towards the north, which expands the surface area on the southern side. At the same time, the ridge is raised so that the solar panel roof is angled perfectly for maximum sun exposure during the winter, when energy demand is at its peak. In Minnesota, an angle of 35° to 45° is usually considered ideal for solar collection during the winter. However, because of competition height restrictions, this roof pitch was too steep for the ICON House. We used energy modeling software to determine that a roof angle of 28° in addition to a certain amount of surface area on the southern half of the roof would produce the greatest amount of solar energy in our case.

Climate

Brutally cold Minnesota winters lead to very high heating needs. However, potentially hot, humid weather during the Solar Decathlon in Washington, D.C. creates a very different set of needs. The ICON Solar House must perform under both conditions, so to meet this challenge we need a thermal system that is optimally sized for both the Solar Decathlon competition in D.C., and for the Minnesota climate.

Integrated Design

It has been said that technology and architectural meaning cannot be reconciled, but this is a narrow interpretation, it does not take into account technological elements that work to create meaning as well as function. If a building is unable to incorporate its functional thermal system into the larger meaning, how then can the structural walls and posts be said to factor into meaning in a more relevant way?

In the ICON Solar House, every move both references cultural meaning in housing and provides functional performance. The integrated shelving system runs the entire length of the house, incorporating lighting, HVAC ductwork, partitions and doors. This shelving unit is a meaningful presence as well, acting as the threshold for entry, and serving as the partition that defines public and private boundaries.

The design of the envelope further demonstrates the integration of performance and aesthetics. The use of a rainscreen instead of siding allows air movement behind the cladding material, helping to draw away moisture from the membrane and plywood sheathing while still allowing the wall to permeate moisture vapor. At the same time, the rainscreen wall addresses the aesthetic goals of the house and the project concept, with horizontal slats that have a similar pattern as traditional wood siding. Unlike lapped siding, however, these spaced slats create the appearance of a more delicate screen, which becomes an important aesthetic element of the house.

Life Cycle Assessment

Life cycle assessment (LCA) is a quantitative measure of the environmental impacts associated with a product over the course of its entire existence. Using data from the various phases of a productís life, researchers can sum up the embodied energy of a product (for example, the amount of energy required for the extraction of raw materials, energy used during the refining process, during fabrication and transport between different phases, energy required for installation and use, and finally, the amount of energy required for disposal) as well as quantify the environmental impact of a product in a variety of categories (for example, human cancer rates, rainwater acidification, water use, soil toxicity, etc).

What does this mean for the designer, builder, or homeowner? Typically, people who want to be sensitive to the environment make product and material decisions based on advertised attributes such as recycled content. The problem with using attributes as the selection criteria is that they can sometimes neglect the extended effects of the creation of a product. Is a compressed fiber cladding shipped from overseas a better choice than a local hardwood lap siding? When life cycle costs of these products are taken into consideration, the hardwood may turn out to be less energy-intensive choice, the choice with a lower total amount of embodied energy. LCA enables comparisons on a quantitative level.

Currently, the biggest challenge with LCA is available data. In order to compare two products, we need numbers from the manufacturer on all inputs and emissions to air, land, and water. However, a growing number of companies are interested in performing LCA because it often exposes inefficiencies in their production processes.

An example of Life Cycle Assessment in the ICON House

Given the necessity of experiencing as little heat loss as possible, we needed a lot of insulation with as high thermal resistance or R-value, as possible. We were concerned about the environmental impact of choosing high-petroleum content insulation such as closed-cell polyurethane. We investigated icynene foams as an alternative, due to the fact that the blowing agents are generally less harmful than those of closed-cell foams, and there is less embodied energy within the product.

However, the lower impact, "breathable" insulation would require over 12" of wall structure. In the end, we chose polyurethane closed-cell insulation because it required less wall structure, allowing the walls to be thinner, and provided an additional benefit of rigidity for shipping and transport, a necessity in the case of a house that will do a lot of travelling.

In this case we may have chosen the more energy-intensive closed-cell insulation, but our particular needs seemed to dictate this decision. However, our LCA research and our own decision-making process will be documented in a database of materials, which will allow people to learn and select materials for their own projects, based on their particular needs.