Maximize your Energy Points with these 7 Questions for your Energy Modeler
The PDF can be downloaded through the link at the bottom of this article.
Is your LEED or Green Globes energy model getting the points your project deserves?
In sustainability certification programs, like LEED or Green Globes, the energy model-related credits may significantly impact both the overall score and the cost of certification. Up to 36% (18 points) of a LEED v4 BD & C silver project might come from the energy model (via Optimize Energy Performance). The energy modeling results will also dictate the amount of Green Power needed, the end uses that need monitoring (under Advanced Energy Metering), and how much solar photovoltaic (PV) capacity (or other renewable energy source) is needed to meet the criteria for points under Renewable Energy Production. Besides these, there are other credits with significant associated costs that may be pursued if the project needs to hit the certification target.
Though the modeling guidelines and requirements are quite clear, perhaps more so than other credits, energy modeling has inherent subjectivity. In other words, two different energy modelers can model the same building with the same software, while both using valid approaches, and end up with two different savings and point outcomes.
In a perfect world, every LEED or Green Globes project would get an experienced energy modeler who knows all the tricks of the trade. This perfect world energy modeler has the time and systems to ensure the points for the certification are maximized, giving the rest of the team optimal flexibility in completing the remaining aspects of the certification target. However, this is not always the case; energy modeling is hard, modelers are human (a.k.a. imperfect), and there are multiple viable ways to characterize a new building’s energy use so that it complies with modeling requirements.
The following list of questions is intended as a checklist for LEED and Green Globes teams; it is meant to help ensure the value of the energy model is maximized. With a maximized value, the otherwise challenging job of certification becomes a little easier, the cost to owners is reduced (hopefully incentivizing them to certify their next project), and, just maybe, it gets the project closer to the next level of certification and possibly drive additional sustainability investments.
1. Has the energy model been Quality Checked by a 2nd person?
As an energy modeler works on a project for days or weeks at a time, he or she may experience the inability to see outside of his or her bias, or, sometimes, errors. Even with formal Quality Check (QC) checklists and years of experience under the energy modeler’s belt, using a second person for QC review is almost always essential to finding issues or improving analyzed savings in the model.
A good QC reviewer will be asking the following questions to themselves during their review:
Are the baseline inputs compliant with modeling requirements?
Where are the savings and penalties coming from? Do they make sense relative to the design?
How do the HVAC system capacities compare between Baseline and Proposed?
Is the sequence of operation of HVAC equipment adequately modeled?
Have you considered X, Y, Z strategies that might improve savings?
Have you accounted for A, B, C common review questions that could negatively impact the score?
Even though it might not be the energy modeler’s firm’s policy to do a 2nd person QC review, it often results in notable improvements. Even if it does not improve savings, it reduces the volatility of the review process and helps to ensure the accuracy of point projections.
To avoid credit submission delays, it is recommended that any QC expectations are communicated to the energy modeler ahead of time. This allows the modeler to arrange his or her schedule and internal resources to meet requirements and stick to the schedule. If the modeler does not have the bandwidth to support this effort, a 3rd party review team may be taken into consideration. Reviewing a model takes much less time than creating it, so review costs should be much less than the initial modeling fee.
2. Have all forms of schedules been evaluated?
“Schedules” within an energy model are set up for each internal load, operating piece of equipment, and thermostatically controlled device. These schedules dictate when and how equipment runs for each hour of annual energy simulation. Accordingly, schedules are among the most impactful inputs to the final outcomes of the model.
The modeling requirements for schedules in both LEED and Green Globes projects state, “The schedules shall be typical of the proposed building type as determined by the designer and approved by the rating authority.” In other words, this translates to, “get input from the designer and use a reasonable schedule.” Can you see why there is subjectivity in energy modeling?
Though the design input is listed as required, many energy modelers resort to using standard schedules, either from ASHRAE standards or from similar previous projects, which are broadly applied to the current project. This saves the modeler time in model creation, but a closer examination may help improve the energy savings of the model.
The best practice is to list the different space types, examine the schedules assigned to them, and determine their respective appropriateness. Good questions to ask in this examination include the following:
Does the fraction of emergency lights line up with the unoccupied diversity fraction of my lighting schedule?
Do my continuously illuminated spaces have a schedule that reflects the emergency lights/unoccupied diversity? How about the infrequently occupied spaces?
Should the private offices have a different schedule than the open office spaces?
Are the equipment schedules realistic? Do IDF, MDF, and server room spaces to draw this much power all the time?
What is the temperature setback strategy of the building? Do the air-side and water-side HVAC equipment reflect this?
Does seasonal variability affect how the building is used?
The goals of the examination are to understand how the building is expected to use and save energy at the space level and to determine if the right schedule is used. To be clear, changing schedules for the sole purpose of maximizing savings is highly unethical. However, because schedules are educated guesses of the building use in many instances, there is nothing wrong with refining schedules and expecting them to improve the savings (if the designer approves, of course).
A quick meeting with the design team, owner, and energy modeler is recommended to review this topic. The energy modeler should be able to extract key inputs to understand how current and future schedule changes impact the savings.
3. Have both interior lighting power allowance options been examined?
LEED and Green Globes both normally use ASHRAE 90.1-2010 as the baseline for an energy model. This standard presents two different methods for determining the interior lighting baseline allowance: the Building Area (BA) method and the Space by Space (SBS) method.
The BA method assigns a single baseline lighting power density (LPD) value, based on the primary building type or function, whereas the SBS method gives each unique space in the model a different LPD, according to the space type.
From a modeling standpoint, depending on the sophistication of the energy modeler’s tools, it is usually much easier and less time consuming to use the Building Area (BA) method. To be fair, in many cases, the weighted average LPD of the SBS method ends up similar to the BA method’s, and the difference in the two approaches may be negligible. In other cases, however, the differences can be significant, and the right approach can positively impact the score of the energy model.
Here is an example:
In hotel buildings, the BA allowance is 1 W/ft2 and the SBS method’s allowance varies by space type. In the corridors, which make up a significant percentage of the area, the SBS allowance is 0.66 W/ft2. Since those areas are illuminated constantly, while guest rooms have much less usage, a large percentage of the lighting energy most likely comes from the corridors. In this case, the modeler likely benefits from using the BA method.
In other situations, the opposite may be true. For example, an office building with significant laboratory space (1.81 W/ft2 in SBS) is likely to get a higher allowance with the SBS than just using the 0.90 W/ft2 BA value.
The ease of formally checking both allowance calculations depends on the modeler’s tools. In some cases, it may take a significant amount of time to add in a new baseline allowance, especially with SBS. However, an informal spreadsheet calculation is normally accurate enough to tell which option is better for the project, and this should not take much time.
4. Have exceptional calculations and non-traditional efficiency opportunities been captured?
Above and beyond documenting the envelope, lighting, HVAC, and service water heating efficiency categories, certification programs normally permit additional energy efficiency calculations to demonstrate additional savings. In LEED, this is called “exceptional calculations”.
These are upgraded control strategies, which go above and beyond ASHRAE 90.1-2010, such as demand-controlled ventilation or static pressure reset, or non-regulated equipment with verifiable efficiency differences and energy savings.
Examples of non-regulated equipment are wide ranging and may include, but are not limited to, the following: kitchen and refrigeration equipment, air compressors or dryers, vacuum pumps, data center/IT equipment, manufacturing equipment, and/or passive solar features.
“Do we have other energy efficient equipment we’ve missed?”
A good strategy to uncover this equipment, particularly if the energy modeler is stuck, is to schedule a meeting on the topic with project team members who are familiar with these different topics. It is important to ask, “Do we have other energy efficient equipment we’ve missed?” These areas could include the MEP engineers, the kitchen, refrigeration, industrial equipment reps, and/or key owner’s representatives, like the I.T. and manufacturing leaders.
Once the opportunities are uncovered, the energy modeler should be able to do some quick hand calculations to ballpark the savings. It is then possible to determine what difference they make in the score and if they should be fully pursued. In many cases, the additional savings can add multiple points to the score.
5. Have different forms of possible utility rates been checked?
With both LEED and Green Globes, cost savings is typically used to determine the savings percentages and, therefore, the awarded points. An energy model may either use actual, local utility rates or average rates, as published through EIA.gov or equivalent for international projects. While both approaches are completely viable, the differences may be significant.
For electricity costs, EIA provides a flat $/kWh rate. The actual rate may have a peak demand (kW) component and/or time of use rate structure. These peak and time-of-use components of the electric rate are becoming more common as utility companies adapt to the growing usage and greater distribution of PV on their grids, as well as the phasing out of antiquated fossil fuel power plants. A savvy design team may take the utility tariff environment into account in their design by using technology that reduces demand or shifts loads into off-peak hours. In this scenario, the energy model maximizes savings by adding in the actual rate to capture more of the benefits of the design. Additionally, the project may be in the service area of a smaller utility company, whose rates differ significantly from the state average.
“Select the utility rate option that benefits the score the most.”
The energy modeler should select the utility rate option that benefits the project the most. It should not take the energy modeler long to import both types of rate structures and simulate the baseline and proposed buildings to find which provides more points for the project.
6. Have Pilot Credits that could benefit the energy modeling score been investigated?
Experienced professionals in the certification process are aware of the number of established pilot credits that may be utilized to benefit a specific project. A particularly powerful pilot credit for LEED’s Optimized Energy Performance Credit is EAP95, the Alternative Energy Performance Metric.
This pilot credit, whose framework was likely used in developing LEED v4.1 scoring system, allows greenhouse gas, source energy, and/or time dependent valuation (TDV) energy to be used in calculating the savings percentage of a project, in lieu of cost savings. This only makes a difference when a project has more than one fuel source (i.e. electrical and natural gas).
As shown in the figure below, the greenhouse gas portion of EAP95 is determined using regional emission rates published in an EnergyStar® study. In parts of the country with higher percentages of renewable energy in their generation, such as the Northwestern US, this pilot credit is particularly helpful in boosting the savings of the project, especially when the project is experiencing a higher level of electrical savings relative to natural gas or other fuel sources. Completing the EAP95 worksheet to see if it will help the project would not take the energy modeler long.
The equivalent concept within Green Globes is to evaluate each of the four paths within the Assessing Energy Performance (3.3.1.1) category. It is very possible to have a broad range of points outcomes between each of the paths, and each one needs to evaluated to ensure inherent flexibility of the Green Globes rating system is being adequately leveraged.
7. Is there a contingency plan if review comments reduce points?
For certification programs, and especially for LEED, the energy model review comments may be a major hurdle in the overall process. The reviewers are very competent at their job; if the numbers in the documentation do not make sense, the reviewers will recognize this, and the team will need to produce explanations.
Beyond any inconsistencies, there may be aspects of the model that must be handled a certain way, like following a credit interpretation ruling (CIR); these are unexpected and often not well documented. Even experienced modeling teams, after following all the right steps above may run into a comment or issue they were not anticipating.
For these reasons, having a contingency plan within the model acts as a safety net. A contingency plan could be anything from using a conservative control sequence to just including an intentional, known error, like using a slightly worse cooling efficiency than the original. These items can and should be added after the first round of review questions, regardless if the comments impact the score (modelers are trying to maximize the score, after all!). Keeping a ‘card up your sleeve’ for this situation helps to protect the credit from wild point swings and allows the team to remain as close to expectations as possible.
An ideal scenario would be submitting a project for 10 points, defending the comments without many changes, and adding in the contingency, to ultimately wind up with 11 points. However, since the unexpected is possible, the comments might ordinarily reduce the score to 9 points. In this case, the contingency plan keeps the score at 10. This scenario is usually preferred, rather than losing a point from the review process after submitting at 11 and still ending up with 10 after comments.
“Have a contingency plan for the review process to avoid point volatility.”
It is important that this strategy is communicated amongst the team members, so there are no surprises with any stakeholders. The energy modeler should be able to make one or two quick changes to the model to incorporate the contingency plan.
About Craig Green
Craig Green is the managing principal at G2 Energy Solutions, an energy engineering consulting firm based in Phoenix, Arizona. Over the last decade, Craig has had the distinct pleasure of both creating and reviewing dozens energy models for LEED and Green Globes applications.
For questions on the article or to discuss working with G2 Energy Solutions, please contact Craig at 480-637-7900 or craig.green@g2energysolutions.com.
Click below to download the PDF: