The Process of Energy Modeling – Part III

greenwaltBy Paul Greenwalt

Wood Harbinger’s engineers have been blogging since 2013! This Throwback Thursday series features posts from back in the day that are just too good to stay at the back of the blog. Enjoy this one by Paul Greenwalt, originally published on January 21, 2014:

In the previous parts of this series, I have explained the process of building energy modeling and when it is important or beneficial to utilize an energy model for a project.  In this third and final part of The Process of Energy Modeling, I am revealing a few tips and hidden benefits of energy modeling!

After you have entered all of your building information and you think you have it all dialed in, export your Annual Energy Consumption report to a spreadsheet and generate a pie chart for visual inspection.  On one of my first projects, I found that my lighting power consumption was almost non-existent!  After some investigating, I discovered that I had mistakenly deleted the lighting power out of most of my rooms!

The graph below helped me discover the error:


When I first started performing load calculations and running energy models, I found myself chasing my own tail trying to isolate problems in the model.  Eventually, I scrapped the plagued model and started fresh.  I dedicated myself to perfecting the proposed case before embarking on the creation of the baseline case.  This led me to two discoveries.  First, it is a great deal easier to construct the model with all of the information compiled and appropriately organized and  second, if you can hold off on building the baseline case until the proposed case is well in-hand, you will encounter fewer errors once you expand your model to include the baseline!

Energy modeling gives you the ability to quickly compare equipment to one another.  But the nameplate efficiency, or factory tested efficiency, is just that; no energy modeling program can truly evaluate real life.  Thus, comparing individual pieces of equipment can only demonstrate the monetary benefit, in rough order of magnitude (ROM), that higher equipment efficiencies provide for the building owner.  This is opposed to system design changes that may or may not have better equipment efficiencies, but have much higher system efficiencies.

The biggest money savers are lighting (which on average accounts for 25% of the building energy usage) and space temperature setpoints.  Installing LED lighting can be expensive (costs are coming down as production and price point competition increase), but this can reduce lighting power consumption by up to half, saving nearly 10% of the annual dollars spent on energy. Turning thermostat settings down to 65°F instead of 68°F can save a great deal of heating energy in the winter, while turning it up to 75°F instead of 72°F can save cooling energy in the summer.  Some occupants may be slightly uncomfortable at first, but appropriate clothing can be the huge energy saver for your client.  Both of these examples can be easily modeled and add instant value to your integrated design team!

An important thing to keep in mind is that your energy model is a complicated and expensive tool.  While it can add benefits originally unseen, it is easy to get carried away and lose sight of the purpose of the particular model you are developing.  If you are running a simple simulation to compare two separate building envelopes, it is not necessary to drill down to the minute details.  Equipment efficiencies, schedules, internal loads, etc. should all be the same in both cases; this is a comparative analysis.  However, careful attention should be paid to the components of the envelope and the construction techniques in order to achieve maximum benefit and accuracy.

When it comes to entering information for your project, the proposed or existing building envelopes, the exterior of a building (i.e. windows, walls, doors, roof and floors) are often the last ones to be acquired either due to missing existing drawings from the old building or the architect not providing up-to-date envelope details.  Once you finally receive all of the information that you need and enter it into the model, you find that the details show significant thermal breaks and by your calculation, the wall, window, or roof is no better than the baseline case!  Even worse is a model that shows nearly perfect insulation, but the modeler has missed a subtle piece of information.  For example, a catalog cut shows windows with a great U-factor (heat transfer coefficient) that is reported as COG or center-of-glass, not the U-factor of the entire window assembly.  This is an extremely valuable part of the design process that you should be used to your benefit.  Recommend that the architect specify better windows or provide more insulation for lowered heating costs.  This will add value to your energy model and save the owner money in the end.

The energy modeling program you use most likely has the option to run shorter simulations (reduced year).  Take advantage of this!  It will save having to wait an hour for results and forgetting what you changed!

The take away from this can be summed up in three words: document, document, document!!!  If you don’t write it down, it will get lost!  I have spent hours chasing a rabbit only to find that I set an air handler to run 100% outside air.  If you hate writing stuff down, use screenshots  to help remember settings or changes.

Take a class on the energy modeling software you are using.  You may know a great deal about it and most of the basics, but the instructors have years of experience and if they can’t answer your question, they can get you to someone who does!

Look for classes offered by ASHRAE, LEED, or your local code jurisdiction.  Often times they will have classes on energy modeling or changes to the code or program that will directly impact your current or future projects.

Well, there you have it!  Now you not only know all about Energy Modeling, it will be your new best friend!  Put these tips to good use and if you have some of your own tips or tricks, please share!  We can all benefit from knowing more!

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One Comment

  1. Posted July 18, 2014 at 3:11 am | Permalink

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