Energy Modeling For Sustainability

Evolving software for modeling energy dynamics makes it easier for architects and engineers to design green buildings
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From GreenSource
B.J. Novitski

Because a complete simulation requires specifying thermal zones and mechanical systems, the venerable DOE-2 has proved daunting for architects to use, particularly early in design, when crucial decisions about form and orientation are made. To make these simulations more accessible, software developers have been creating "friendlier" user interfaces. Systems such as eQUEST (doe2.com/equest), also initiated by DOE, and EnergyPro, offered by the private sector, enable architects and engineers to take advantage of DOE-2's analytic power during schematic design. They do so by offering intelligent defaults for as-yet-undecided design features. As the project develops, these defaults can be replaced by real design proposals, and the analysis becomes incrementally more precise. There is a price to pay, though, for simplicity. eQUEST, for instance, is limited in the complexity of geometry it can model. DOE-2 and EnergyPlus are not alone in their thoroughness and reliability. Trane Trace 700 and the British IES are comparable in calculating loads and sizing mechanical systems. IES goes further still to calculate carbon emissions and provide a computational fluid dynamic (CFD) analysis of airflow between thermal zones. Most energy modeling software supports energy-consumption comparisons among different scenarios to assist in design choices. However, no single software system does it all, and it's common for design firms to draw on several to accomplish a complete simulation. This is particularly important for firms interested in still-out-of-mainstream technologies like photovoltaic cells, ground-source heat pumps, or natural ventilation in commercial buildings.

 

In the design of Stopwaste.org, Rumsey Engineers used eQUEST energy modeling to simulate envelope insulation, glazing, electric lighting, and mechanical systems.

Photo courtesy Rumsey Engineers

 

It's important to note that no simulation is a perfect representation of reality, and any prediction relies on many assumptions about conditions that will affect the operations of the building, such as weather, occupancy rates, and facility management practices. Results from these programs are useful for evaluating design options, but their ability to predict actual energy use is limited and should be tempered by good sense, professional experience, and actual performance data.

 

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Originally published in GreenSource
Originally published in April 2008

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