• Passive Solar Design

    south light

    Passive Solar Design takes advantage of site, climate, and the energy of the sun to provide thermal comfort through heating and cooling. The shape and orientation of buildings, as well as its details and systems are all keys to optimizing passive performance. The strategies vary depending on the specifics of the site, meaning that passive solar buildings are integrated into and appropriate for their locations.

    The site’s location and microclimate impact the building’s form and orientation. Important factors include solar access, harsh wind, weather or fog, relationships to slopes or existing vegetation, and diurnal temperature swings. Generally buildings should have the majority of their glazing facing within 30° of due south, and we find that in most instances the optimal orientation is roughly 17.5° east of due south. This creates a building with more morning gain and less in the afternoons.

    In addition to south-facing glazing, passively heated buildings typically feature high insulation levels and tight construction, shading elements at windows, and thermal mass. Properly sized shading over windows and doors helps to control unwanted solar gain during the hot months. While it is usually best to limit east, west and north facing glazing, modern glazing systems minimize high energy loss or gain penalties in these locations. Thermal mass is defined as a heavy, dense material that can absorb the heat of the sun, and then radiate it back to the space during the evening. Many elements in a building can act as thermal mass, including slab-on-grade floors, thick soil or plaster wall finishes, thick or double gypsum board, and masonry elements such as fireplaces, masonry heaters, or planters.

    Passive cooling similarly features proper shading and thermal mass within the building envelope, as well as operable windows placed to take advantage of natural ventilation. Here in California where nighttime temperatures are lower, night flushing via fans or natural convection (warm air rising) can be used to remove heat stored in the thermal mass from the building. Windows or fan openings are then closed in the morning and the mass helps keep the building cool and comfortable.

    Other passive design features that can reduce the active energy needs of a building include day-lighting, air-to-air heat exchange, radiant barriers, and ventilated roof systems. Employing these passive strategies can reduce or eliminate the mechanical systems, saving both direct costs and long-term energy costs.

    In most climates, buildings can achieve passive comfort for a majority of the time, with needs during extreme periods of weather being met through supplemental systems, ideally from renewable energy resources.  Integrating these passive strategies will continue to be important in the future, as energy codes become more restrictive, and we strive to reach a carbon-neutral built environment.

  • Active Solar Design

    solar hot water

    Active Solar describes energy systems that capture the sun's energy and store it in some manner for later use, through mechanical or electrical means. The two basic types are electrical systems, or photovoltaics, and thermal systems that heat liquid for domestic hot water and/or space heating needs.

    Renewable Electricity Systems
    Residential scale renewable energy typically means electricity generation via photovoltaic panels, but if the conditions allow, wind or micro-hydro are attractive renewable energy options. The discussion here is focused on photovoltaic (PV) systems.

    Framed PV panels are the most common form of photovoltaic energy collection. These panels laminate solar cells (thin slices of mono-crystalline or polycrystalline silicone) onto glass surfaces that are interconnected into arrays generating DC (direct current) electrical energy, typically between 12 and 48 volts, though some grid-intertie inverters operate at higher voltages. An inverter converts the DC current into typical household AC (alternating current) 120 volt power.

    The average California household uses 19 kWh (kiloWatt-hours) of electricity per day. With some basic energy conservation (efficient lighting and appliances, limited or no air conditioning, and conscious use) a household should be able to get that use down to 10 kWh or less. A 250 SF rooftop- or ground-mounted system (2.5 kW) could cover this energy use.

    Optimal orientation and slope depend on ones latitude and weather patterns; here in the San Francisco Bay Area the optimal angle for a fixed array facing due south is approximately 30° above horizontal. With seasonally adjusted panels, one can achieve an additional 10% of production. Fully tracking arrays can increase output by about 35% at our latitude, but tracking systems are prone to significant maintenance.

    Many companies offer lease programs, where they will install and maintain your panels.  The resident benefits for the power produced, and reduced energy bills, while the company gathers any rebates.  For more information about rebates in California, see gosolarcalifornia.ca.gov.

    Solar Thermal Systems
    Collecting heat from the sun and storing it in the form of water is the most typical active thermal system.  Stored heat can be used for domestic hot water and/or space heating. There are a few basic variations we employ, but we aren't limited to these.

    Batch collectors use domestic water pressure to push fresh water through the hot water collector, for domestic needs. This type of collector can only be used in climates that do not experience hard freezes. When the tap is turned on, heated water is pushed from the panel to the faucet where it is replaced with cool, incoming water. Often this is piped through a hot water heater, either to pre-heat water in a tank heater, or through a solar-calibrated instant hot water heater, which doesn't turn on if the water is already hot.

    Solar hot water systems in freezing climates will typically feature a closed loop system running anti-freeze (glycol) treated water through the collectors to a heat exchanger which in turn heats water in a solar storage tank. Unless the tank is located above the panel, this water must be pumped mechanically, either with a thermostatically controlled pump, or a 12V DC pump powered by a photovoltaic panel.

    Space heating can be accomplished with a variation on the closed loop option, by increasing the size of the collector array and, following the heat exchange, piping some of the heated fluid through tubing that is buried in a 2-3' deep insulated bed of sand beneath the floor slabs. This combined solar direct hot water and space heating system was pioneered by Shelter Systems in Wisconsin, and made popular by Bob Ramlow. (This system and all things related are discussed in Bob's book, Solar Water Heating). We've combined this system with masonry heaters and wood-burning boilers as well as with air-source and geo-exchange heat pumps.

  • Straw Bale

    Window in plastered straw bale wall
    bale raising party

    When considering ecologically sound construction methods and materials, few if any have as many layers of redeeming value as straw-bale construction. The raw material is 100% waste of another industry, the growing of grain for food, and in many cases is otherwise burned, causing serious pollution. The material is packaged in a convenient and user-friendly form. The substitution of bales for lumber can relieve the pressure to log old-growth forests, preserving ecosystems for wildlife habitat, air-quality and soil-stabilization. Additionally, building with straw results in net-carbon sequestering, critical as we face growing carbon driven climate change.

    Straw-bale construction is a proven durable method. Homesteaders in the Great Plains started building with bales in the late 1800’s, and many of these structures still stand today. Properly built and maintained, straw buildings can have a useful life span of at least 100 years.

    Straw bale construction places all of the wall elements in the right location for high thermal performance: a protective layer on the outside, ample insulation at the center, and thermal mass to the interior. Unlike similar foam-based wall system, the bales are natural, healthy and rapidly renewable. When laid flat and stacked like bricks in a ‘running bond’ pattern, a plastered straw-bale wall is ±27" thick. Stacked ‘on edge’, with straw parallel to the plane of the wall, an R-30 insulation level is achieved in 25% less width (±18"). This is several times the value of typical insulated wood wall. The cost of construction with straw-bales is comparable or less than other thick-walled construction systems. When energy savings over time are factored in, straw-bale is the economical choice. One family in California's hot Central Valley was able to obtain a higher mortgage for their straw-bale home by showing that their cooling costs would be substantially less.

    Straw-bale can have great aesthetic value, and lends itself to a variety of styles and finishes. The thick walls present opportunities for niches, deep windowsills and seating areas, and “truth windows”. And, as Matts Myhrman once said, "You can do anything with straw-bales, except have skinny walls!"

  • Earth

    Detail of rammed earth wall at Hidden Villa
    pise formwork

    In the right circumstances monolithic earth walls are an effective construction system, providing durable walls that mediate daily and seasonal temperature swings. Earth construction may well be the oldest method of building in the world, as ancient cities of Mesopotamia were built of rammed earth and stone. It is the quintessential local building material, with a large variety of types and styles suited to an equally large variety of climates and soil types.

    We are familiar with several of these systems – including adobe, light straw-clay, cob, and hybrid adobe – but in our practice we have most frequently worked with rammed earth or the sprayed soil-cement variation known as PISE. Soil-cement is typically reinforced, and stabilized with cement or lime, important when working in locations with seismic concerns. Another option for seismically active locations is Watershed Block, a product from David Easton that uses native soils to create a standard masonry unit with natural color variations.

    Without an insulating layer, monolithic earth construction should only be used in relatively mild climates and with careful attention to solar orientation, shading and passive design. The mass helps mediate diurnal temperature swings, but spaces may become too warm or cool during unseasonable periods of weather. We generally prefer to use earth as a finish on straw-bale or other insulating systems, or as a thermal mass wall within an insulating envelope. This way the full benefits of the earthen walls are enjoyed in a wider variety of climatic conditions.

    Aesthetically a variety of textures and finishes can be achieved depending on technique – from the striations of a rammed earth wall, to a textured or troweled sprayed wall – giving structures a natural, timeless quality.