Energy efficiency - best investment for our energy future

Posted Wednesday, July 24, 2013 in Sustainable Maine

Energy efficiency - best investment for our energy future

Terrahause, a Passive House project at Unity College.

by Paul Kando

Being energy efficient does not mean sacrificing comfort, like turning the thermostat down and feeling cold all winter: it means more comfort while consuming less energy, intelligently applied technology to reduce the energy demand of a house to near zero, without relinquishing comfort. One could literally freeze sacrificing comfort yet not save even 25 percent, while improved energy efficiency routinely reduces the energy consumption of houses by as much as 90 percent.

The potential for improving energy efficiency is often underestimated. It could cut US energy consumption 23 percent by 2020, saving $680 billion and abating 1.1 gigatons (1,100,000,000 tons) of greenhouse gas emissions annually. Energy efficiency is essential to ensure that the use of renewable energy offsets rather than supplements fossil fuel use. A Passive House (PH) rated window reduces heat losses by more than 70 percent in comparison with an ordinary double pane window. Proper insulation can reduce heat losses by up to 90 percent through an external wall.  An efficient heat recovery ventilation system reduces ventilation heat losses by 80 to 90 percent. Such measures will help achieve high levels of energy efficiency and minimal energy consumption in a building.

Energy efficient buildings are characterized by high levels of insulation around the heated envelope; no (or minimal) thermal bridges across the insulated envelope; air-tightness; heat recovery ventilation; and high performance windows and doors. New PHs are designed to use no more than 15 kWh/m2 of heated floor space/year for heating or cooling; 120 kWh/m2 of heated floor space/year total primary energy consumption; 0.6 air changes per hour at a 50 Pascal indoor-outdoor pressure difference (as measured by a blower door). They maintain a comfort temperature of 20ºC (68ºF), no less than 90 percent of the time. A house that meets these requirements will use 90 percent less energy than its conventional counterparts.

Existing buildings can be upgraded to similar standards. However, depending on the condition of a building (as determined by a professional energy audit), such an upgrade may only be economically feasible in conjunction with major remodeling or rehabilitation. As an alternative, “low hanging fruit” efficiency measures always make sense, as long as these “move the building” closer to PH performance.

 Efficiency can be improved wherever energy is used. It means permanently replacing annual energy consumption with a one-time investment in intelligent, innovative products and clever process management. The required measures can often be combined with maintenance or remodeling tasks. It is foolish not to add thermal insulation when a wall is being repaired; or a room is added -- insulation is always less expensive than the energy it saves. Sealing and insulating basement ceilings and attics is always a good idea. A one-time investment in high levels of energy efficiency pays off from repeated annual savings. The required products can be manufactured locally, creating employment and encouraging innovation.

When it comes to windows, replacement is not always the best option. By all means replace old single-pane windows if they are in poor condition. However if a window is otherwise in good shape, interior storm windows, because of their low cost, may be a better deal. If you do replace a window, the replacement should be the most energy efficient model available. A PH- rated window may be marginally more expensive to buy, however the labor of replacing a window usually costs more than the marginal price difference between the cheapest and the best window you can buy. Paying someone to install a poor-performing window makes no sense.

Conventional builders approach energy efficiency by adding more insulation, and other energy improvements to a conventionally constructed building, skipping the planning process which is key to PH construction. The result is often more expensive, less efficient, or both. Moisture problems are especially common.

PH construction is fundamentally different. It combines 21st century building methods and science with sophisticated information technology. All technical decisions (including choice of materials and even appliances) are made in the design phase, during which everything is system- and cost-optimized by computer-simulation. These houses are usually built by designer-builders who employ small, well-trained and well-supervised crews at the building site. The building is performance-tested (not just inspected) throughout the construction phase. Subcontractors – the staple of conventional building -- tend to be absent, or restricted to very narrowly defined tasks. It makes absolutely no economic sense to newly build anything less efficient than a PH.

Existing houses may be upgraded to maximize energy efficiency. This can’t be done without knowing the current state and performance of the building. The key is a professional energy audit, based on which a comprehensive efficiency-improvement plan, specific to the building, can be made. When remodeling or additions are planned, it makes sense to upgrade an existing house to PH standards.    

Even if the residual energy demand of an efficient house is met by fossil fuels, lower energy use means stretching supplies and minimizing environmental impact. A much better way, however, is to meet the residual demand from renewable energy sources. The best bang for the energy buck is always improved efficiency. After that the renewable energy part can be sized to meet a smaller demand.

Architects, designers, builders and craftsmen who update their construction approach will benefit greatly from the inevitable spread of PH technology – and their 21st Century expertise will be in demand.

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