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Case Studies: Solar Thermal Residence

GENERAL INFORMATION

Project name: Solar Thermal Residence

Location: Twin Cities Metro, MN

Architect: Locus Architecture, Ltd.

Builder: Katie Rose Construction

Building size: 4800 sf house, 390 sf garage

Building use: Private Residence

Completion date: January 2007

OVERVIEW

This project demonstrates how solar thermal heating can be integrated into the design of the structure. This renovation project included additions to the original early 20th century structure. The owners established initial goals with the Locus Architecture team to retain some of the original structure. Together, they set project goals for utilizing an attractive design to incorporate energy efficiency, renewable energy, and durability intone. The renewable energy system collects the sun's energy to provide domestic hot water and space heating. The house was restructured to increase the square footage while transforming it into high performance building.

BUILDING PERFORMANCE

Effective energy use solutions: The energy efficiency strategies integrated by Locus Architecture included ENERGY STAR rated, high efficiency appliances as well as an ENERGY STAR rated roof material. The design strategies included aspects such as super insulation, natural ventilation and daylighting.

Orientation: The solar collector array faces south, while the primary structure faces east and west, as it is a renovation of an existing lot and building.

Daylighting strategies: The house is fully daylit by several clerestory windows, an open floor plan, and all of the bedrooms have at least two to three exterior wall windows. As the site provided natural shading, Locus capitalized on the views available to bring in daylight without impacting the solar heating load.

Passive Cooling Strategies:

  • The natural ventilation strategy incorporates the windows from lower and upper levels.
  • The multiple bedroom windows increase cross ventilation.
  • "The building's three tall spaces (the flat roof section over the stair, the tall spaces on the south side, and the space over the garage) all use convective stack-effect to ventilate and cool the house in the warmer summer months. Stack-effect works according to the pressure differences of warm and cool air. In the summer, cool air is drawn in via windows and doors at the lower level while warmer air floats up - due to the natural flow of lighter warmer air - and is flushed out at windows high in the house. The upper windows and open ceilings work best when they are as high as possible. Wind velocity increases with height, the higher the windows are, the more stack-effect is generated."

Source Document: Locus Architecture Energy Efficiency Strategies

Shading of structure: The site has deciduous trees heavily shading to the west, a large maple tree to the east, and low shade to the south.

Envelope: Exceeds code by 30%

Wall thickness: 10" average (range from 5"-14")

Roof: ENERGY STAR (light cool color to reflect solar energy, approximately 85% of total roof area) painted steel standing-seam roof. This roofing material is fully recyclable, very durable, and should have an installed life of at least 40 years.

Insulation R-values:

  • Roof R-50: foamed several inches with cellulose blown in over foam
  • Walls R-34 foam: closed cell polyicocanyurate, 2" rigid insulation on exterior for continuous thermal envelope

Windows:

  • Larger picture windows were triple pane
  • Rest of the house: double low-e argon heat smart 2

Climate control systems:

  • Primarily natural ventilation for the summer. The office/bedroom has dedicated cooling and air filtration, however, air conditioning is possible for the whole house.
  • "The home is heated by a high efficiency boiler using a combination of solar energy and natural gas. All the heating will be delivered via radiant heat, with no forced air. Radiant heating delivers more comfortable heat per BTU than comparable forced air systems, and typically uses less fuel."
  • The radiant floor delivery system is called Warm Board for wood floors.

Source Document: Locus Architecture Energy Efficiency Strategies

Backup heating/power:

  • Backup heating with a high efficiency gas
  • Electric back up for domestic hot water
  • Garage heated by a gas fired blower

RENEWABLE ENERGY SYSTEM INFORMATION

Solar system description and size:

  • Solar thermal drain-back system for space heating and domestic hot water
  • Three 120 Gallon Rheem storage tanks
  • Eight 4'x 8' (256 sf) AET flat plate collectors installed at 60 degree angle
  • Grundfos pump 2699
  • 15 gallon Eagle Solar drain back tank (see diagrams)
  • Storage tanks and the lines to the heating system are separate for the domestic hot water and space heating for code reasons

Solar system cost: Approximately $32,000

Payback: 20 year return on investment, $400/year initial savings increasing with inflation rates of natural gas

Date installation was completed: Winter 2006

System designer: Innovative Power Systems (IPS), in conjunction with Gausman & Moore

Engineer: Jim Keller, Gausman & Moore

Installer: IPS

Estimated amount of energy delivered by system: Approximately 400 therms/year

Percent of building's total energy use provided by solar: 40% of heating load

TOOLS UTILIZED

Modeling software:

  • Daylighting by Locus
  • Energy Performance conducted by Gausman and Moore
  • Renewable Energy: Fchart and Visidrawings by IPS

Models constructed: Locus Architecture built a physical model with a sun peg for light modeling and shadows cast onto neighboring properties

MOTIVATION FOR INSTALLATION

"One of the options initially considered was tearing down the house and building new. Upon review, the owners declined to pursue this path for a number of reasons. First, they felt a significant demolition would be drastic - both to them and their friends and neighbors. Second, they felt it wasteful to demolish a house with "good bones", one built on a solid foundation with quality framing materials. Third, they wanted to save as many of the site's valuable trees as possible - an impossible task if removing the existing house entirely.

When initially working with Locus, the owners encouraged them to design a house that fit conceptually with other buildings on the block. They asked for a house built to last - physically and aesthetically - for decades, even centuries. In addition, they asked Locus to employ design strategies to harness the technologies and materials available in the 21st century.

The owners' interest for the view, then allowed Locus to provide ample glazing for opening up the view, which in turn increased the daylighting opportunities.

In the end, the owners requested that the design address energy efficiency strategies and to be resource efficient."

Source Document: Locus Architecture Energy Efficiency Strategies

LESSONS LEARNED

The choices made during the project required communication between multiple parties - the owner, architects, engineers, renewable energy installers, and the contractor. The following recommendations are combined from interviews with the architect and renewable energy system installer and relate to the nature of the design process for incorporating renewable technologies and then implementing the designs selected.

  • From the beginning it is important to incorporate the contractors into the process to get them onboard with what is going on. This means bringing in the general contractor as soon as possible, as well as the mechanical and structural contractors to work together with the renewable energy installers. It is really important to work with people who know what they are doing with renewable energy systems. This will help provide a positive experience with the process which is necessary to get the general contractor to continue to be involved in including renewable energy in projects and to encourage their influence in the market.
  • While incorporating renewable technologies, it is also important to make sure all the easy things are addressed, such as better insulation, smaller footprint, and shaping the volume for passive heating and cooling reasons.
  • Establish a relative budget to design, install, and select types of renewable technologies for practical purposes. This means being able to decide from the beginning about the option chosen and not continuing to add new options.
  • Design keeps changing for the renewable energy system as other elements of the building change. Delivering the product becomes more challenging and requires more coordination if the design is not locked in earlier in the project. Again, this is why the renewable energy system needs to be part of the dialogue during the design phase.
  • During the design phase, there were conflicting desires between the owner's desires for solar thermal heating and the use of carpet and how to deliver the heating in conjunction. The end result was that the active solar thermal heating system was combined with a product called Warm Board and a dense wood species.
  • In the construction phase when several contractors are involved, it is important that one party is in charge of the entire operation. This would make clear what everyone's role would be, based on the system designer's recommendations.
  • The collector installation went very smoothly because the roof was designed specifically for the collectors chosen. The outcome of the installation is working well and performance is good.
  • Once everything was installed it was essential for the heating system designer and the solar system designer to fine tune system controls on site. This ensures that the solar system is the primary heat source and that the fossil fuel system acts as a backup.
  • A successful approach was taken for engaging the neighbors to be exposed to the project and learn about the design choices that included renewable energy and high performance building:
    • "Because some of these materials and technologies do differ from the materials and technologies available to early twentieth century homes like others on the block, the owners invited the neighborhood to review the plans, elevations, and a building model of the proposal (with the flat-roofed stair tower design) in 2005. Many of their neighbors stopped in, and I spent several hours answering questions about the design, the mechanical systems, the roofs, as well as the shape of the exterior and how it was derived. To my knowledge, the neighbors have been supportive of the project. Anecdotally, from what the owners and I have heard, the neighbors view the project favorably - at least in part due to the environmental aspects of the design." (Wynne Yelland, Locus Architecture: Source Document: Locus Architecture Energy Efficiency Strategies)
  • This lesson is essential in order for renewable technologies to gain more support in the industry and in residential communities. When introducing new ideas to a community, more support for the project can be gained by sharing with community members, by educating them about the rationale for the choices made, and answering their questions while addressing their concerns.

OTHER INFORMATION

Other Sustainable Features:

  • Many of the choices made were to build a building that would last and be energy efficient.
  • 14'x7' Green Roof @ 8-9% of the overall roof area

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