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June 2, 2011 -
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Today's tip from Building Operating Management: Energy models are valuable in achieving high performance HVAC designs.
How efficient can a building’s HVAC system be? To a very large extent, the answer depends on other factors in the building. The type of windows, the amount of insulation, the lighting system, the reflectivity of the roof — these factors and others like them can constrain the performance of the HVAC system by requiring it to work harder to heat and cool the building.
Today, it is possible to evaluate the HVAC impact of these other elements while the building is being designed. Powerful energy modeling software, available from a range of sources, enables the design team to estimate just how efficient a given set of design choices is, and then to compare other designs to identify the one that best meets the building owner's requirements.
For example, Option A may involve code-minimum insulation, ordinary insulated glass windows and a non-reflective roof. Option B, with more insulation, low-emissivity windows and a reflective roof, may initially cost more, but pay for itself in energy savings. What's more, savings associated with a smaller HVAC system can free up funds to cover the cost of those added efficiency measures. In some cases, the energy model may identify options that actually reduce the first cost of the project.
The use of an energy model is required to obtain federal tax deductions under Section 179D of the Internal Revenue Code. These are also known as EPAct tax deductions for the Energy Policy Act of 1995. To qualify for a deduction, an HVAC project must reduce energy costs at least 16.67 percent below the costs for a building designed to meet ASHRAE 90.1-2001. Energy modeling has to show the energy cost savings.
It's important to keep in mind that the energy model, as important as it can be at the design stage, is only an estimate. The actual energy efficiency of a building will depend on how the building systems are operated. A well-designed building can’t overcome poor operation.