Energy modeling is becoming more common place with the design of commercial buildings.  However it is primarily used by the mechanical engineer to design and size their systems.  Very seldom is it used in the early stages of a project as part of the design process for the entire building to maximize the energy efficiency.  In the residential sector of design and construction, energy modeling is rarely used.  It is more common place with Energy Star rated homes, even then it is only used to show compliance with the requirements of Energy Star standards, not a part of the design process.

Energy modeling in new home design, construction and renovations can be a very effective tool to weigh the cost effectiveness of any design strategy used to improve energy efficiency in a home.  Actually most energy auditors use some form of energy modeling to show their customers what kind of financial payback they could expect when implementing any of the recommended improvements.  So why is this tool not used more within the design industry?  Energy modeling is a standard service I provide with any home design work that I do, as well as a service that I provide to other design and construction professionals.  I offer this because some jurisdictions do require an energy compliance certificate.  Granted most design professionals and builders use REScheck as their preferred method.  However, REScheck will only demonstrate compliance using the trade-off approach and the prescriptive packages approach as described in the energy conservation codes.

More advanced software packages such as REM/Design which I use takes this a step further.  REM/Design and other software packages will not only provide you with a compliance certificate, but it will provide design loads along with estimated energy usage and cost to operate the home.  This can be helpful as a preliminary sizing tool for your heating and cooling systems.  What is also valuable about this feature is it gives you the ability to weigh the cost effectiveness of “upgraded” insulation levels or more efficient systems.  The software will even break up the loads into building components, so you know where most of your energy is being lost in the homes envelope.  For instance a recent project I was consulting on, I was able to determine that the six skylights the homeowner wanted in their passive solar home were more of an energy penalty than an overall gain.  So there was a compromise and the number of skylights was reduced to 3 as a daylighting strategy instead of one for heat gain in the winter time.

In an article posted on the American Institute of Architects website (Sustainable AIA: 2031–Why Energy Models Don’t Predict Actual Energy Use), it discusses the criticisms that energy modeling does not predict the actual energy usage of the building or home.  To some degree that is expected, energy modeling simulates the energy usage of a home to determine design loads based upon your geographical region.  Each software package takes into account occupants; however they cannot take into account occupant behavior which has a huge impact on the performance of any building or home.  Of course each software package has its flaws and performs some calculations better than others.

In the coming weeks, Chris Laumer-Giddens with Energy Vanguard in Georgia who is a licensed architect and HVAC designer will tell us the basic differences in some of the more widely used energy modeling tools.