Making Good Choices
A straightforward efficiency target (“I want to be 50% more efficient than code minimum”) may seem like an easy goal, but getting to that goal requires both knowledge and diligence to ensure
that all of the above considerations are factored in and that decisions are supporting goals.
Energy modeling software can be an indispensable ally in this pursuit. A knowledgeable consultant can help to guide choices that have
In this sample worksheet, a building is modeled as though it were built to code minimum standards (56.7kWh/m2a), and compared to a target energy use of 15 kWh/m2a.
A number of changes to the building design are tested in the computer model, and the amount of heating demand reduction achieved by each potential change is noted (column 2). The modelers then make recommendations about whether or not the measure should be carried forward into the final building design (column 3). A As the chart shows, only six of the 14 measures were This type of “fine-tuning” is extremely useful at the de- chosen to meet the desired energy target. Some measures sign phase to help meet energy efficiency targets. did not result in enough performance gain, others resulted in additional gains but were deemed too expensive for the impact they would have.
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Cost and the notion of “payback”
The cost implications of achieving a desired efficiency target are always an important consideration. However, the notion of “payback” tends to be applied to energy efficiency in a way that is inconsistent with other aspects of a home design. While it is common to wonder about the financial payback of additional insulation or better windows, the same question is never asked about house/room size, kitchen cabinetry and countertops, paint, or any other aspect of a home. Too often, the cost of a fancy countertop or luxury tub or shower enclosure outweighs the cost of efficiency measures that were deemed to have insufficient “payback.” While financial payback is one useful metric for making efficiency decisions, factors like environmental impacts (what is the payback of greatly reducing your carbon footprint?), future fuel supplies, indoor air quality, and other considerations can be equally important; a single-minded focus on efficiency payback can result in a project that does not do justice to a full set of goals.
The work of a good energy modeling consultant can provide valuable decision-making information for a homeowner, but it is important to make sure that energy use is monitored once the building is occupied. Actual energy use should be compared to predicted energy use, and troubleshooting undertaken if the real-world results deviate too widely from the model. Improper functioning of equipment/appliances and occupant behavior are the two most common reasons for poor real-world results. The Passive House Institute, developer of one of the world’s foremost energy efficiency standards, has found that “different users have, even if they live in identically constructed houses, frequently very different consumption results: Deviations of ±50% from the average consumption value are not exceptional. This deviation is caused mainly by different thermostat settings during the heating season.”7 This makes it clear that it is not enough to just have efficiency targets during the design process, but that it is important for owners and occupants of buildings to intentionally contribute to efficiency.