Net Zero Energy Building Envelope Design
Net zero energy building envelope design should be of primary importance to every commercial contractor, asserts the Center for Climate and Energy Solutions (CCES). “Space heating, cooling and ventilation,” says the CCES, use up the most energy in commercial sector, and comprise “34% of the energy used onsite.”
Net zero energy, the term used in the title, means that energy efficient measures and design are employed to cut down on energy consumption, and the energy that is used is equal to renewables, such as solar, that are produced on site. A net zero building is ideal because it does not increase the amount of greenhouse gases in the atmosphere.
Homes and commercial structures, according to CCES, emit 38% of U.S. carbon dioxide emissions, a greenhouse gas (GHG) the U.S. desperately wants to reduce. Reaching net zero energy is so crucial that the U.S. Energy Independence and Security Act of 2007 demands that any new commercial construction be net zero no later than 2030.
Composed of the roof, foundation, and walls, the building envelope separates the interior of a building from the outdoors. The CCES asserts that the building envelope should be designed in such a way, and should employ such materials that it acts as a thermal barrier, minimizing heat transfer, so that it requires less energy for heating and cooling. Thus neutralizing the indoor environment, so it is not too warm or too cool. Let’s look at how design can enable this goal.
The design of a structure will determine how much lighting, heating and air conditioning it will need. Engineers and architects should collaborate to select alternative warmth options. “Passive solar heating” uses the rays of the sun, and the positioning of the building to warm the structure. The position depends on the climate. South-facing windows are a boon in the northern hemisphere, and shaded locations in southern locales.
Best Building Envelope Materials
Bio-based products employed in all parts of the building envelope can significantly lower embodied energy. That is the energy needed to “extract, manufacture, transport, install and dispose of building materials.” Using bio-based materials, also reduces greenhouse gas (GHG) emissions.
Insulation and Sealing
Heat transfers from a warmer area to a cooler one, and insulation helps to slow this process. Every insulation, therefore, has a different R-value, which is a measure of the ability to resist the flow of heat. But whether contractors use “blanket, concrete block or forms, spray foam, rigid foam or natural fiber,” insulation, in its capacity as a building envelope support, is useless without the proper air barrier and moisture barrier.
Although insulation slows the transfer of heat, and reduces energy loss, it is not airtight and cannot protect from water and moisture intrusion. A high performance air barrier and moisture barrier resists air movement, and therefore moisture, by increased air tightness. Vapor permeable air barriers allow any moisture within the structure to escape via diffusion. Depending on the membrane, they can also be watertight, resisting moisture intrusion from wind-driven rain. Without the proper air barrier and moisture barrier, the insulation could be at risk from moisture and mold.
Roofs and the Building Envelope
Roofs designed to reflect the heat of the sun can greatly reduce air conditioning costs, whether they be payments to utilities or GHG environmental harm. Roofs of ENERGY STAR materials, often called “cool roofs,” can decrease “peak cooling by 10% to 15%,” declares the Center for Climate and Energy Solutions.
Roofing also presents an opportunity to install, “on-site generation systems.” Solar photovoltaic (PV) arrays can either be installed directly on top of the roof, or integrated using photovoltaic shingles and tiles.
Walls and the Net Zero Concept
Choosing the right materials for walls can be difficult , said the CCES, because the “energy properties of an entire wall are affected by design.” Nevertheless, a structure’s thermal mass, or its capacity for heat storage, is more than somewhat dependent on the materials chosen. Thermal mass structures pull in heat more slowly and retain it longer, thus maintaining even warmth or coolness throughout, and reducing energy consumption. Building products labeled “thermal mass” may be your everyday stone and adobe, or those that use phase change (PCM’s) materials. PCM’s are solid at about 65 degrees, then liquify as they retain heat. PCM’s gain heat during the day and give it off during the cooler night, moderating interior temperatures.
Fenestration, a term that encompasses windows, outside doors, and skylights, influences interior lighting, and the amount of heating/cooling energy needed. Today’s high performance fenestration materials, coatings, and designs, extremely reduce heating and cooling costs. Materials such as, multiply glazed and double-paned (or more) windows, filling the spaces between panes with argon, a low-conductivity gas, and e-window coatings that mute infrared sun rays cut energy use from 10% to 40%, and result in the lowest to maintain commercial construction.
Relying only on efficient products will not produce a net zero building. Reaching net zero energy depends on commercial architects and contractors employing energy-efficient designs and materials in every part of the building envelope.
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