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Building Simulation 2017 Conference – Technical Summary

Building Simulation 2017 Conference – Technical Summary

by Weijun "Allen" Mei

November 14, 2017

Building Simulation 2017 Conference – Technical Summary

In August, I attended my first IBPSA International Conference. It was a three-day parallel session program in which people from different organizations came together to share their knowledge and experience. As an entry level practitioner and an IBPSA newbie, it took me a while to digest what I heard and learned at the conference. I attended approximately 12 sessions over the course of three days and I would like to recap and share what I learned.

#1 The Value of Energy Modeling to Owners and Architects

Building Energy Modeling has been around for a while, with origins in the 1950s and increasing in use since the 1970s. We know the benefits of energy modeling: helping with building design, obtaining permits or LEED certifications, and researchers sometimes use it to assess new systems. However, for most of us, it is not easy to visualize or quantify how beneficial it is.

In one of my sessions, Anica Landreneau of HoK, presented their internal study on energy modeling payback. It was amazing to learn that the average payback is 2 to 3 months! Personally, I think in this industry, 2 to 3 months payback is basically a must.

She also introduced the AIA 2030 vision, which is to design carbon neutral buildings by the year 2030. While society is still debating the merits of climate change, AIA has created a vision and is promoting the future of buildings. From an energy modeler perspective, this is a great challenge to take and I think it will reshape how we think about building design and use.

#2 LEED and Energy Modeling

LEED is widely known and pursued by building owners internationally. The majority of Energy and Atmosphere category points are achieved by energy models. At Cyclone Energy Group, we have helped many of our clients earn LEED Certification of all levels. Through the past several years, we have received and responded to hundreds of LEED comments back on our models. Based on this experience, we know what LEED expectations are as well as their limitations and have established quality control procedures and peer knowledge sharing to streamline the review process.

Gail Hampsmire from the USGBC spoke at one of the sessions in the conference. She noted that many energy models are subject to the “garbage in and garbage out” principal. The lack of thoughtful consideration by energy modelers often leads to models with nonsense results. She suggested that USGBC should establish a certain filter system to single out those poor-quality models.

I strongly agree with what she said. Energy models normally have hundreds to thousands of inputs, which means they could go wrong in every way. And lots of times, it is hard to check all of those assumptions. I think a more comprehensive review process and increasing the requirements for energy modeler credentials, such as the ASHRAE Building Energy Modeling Professional (BEMP), are becoming increasingly important to promote the validity of energy modeling.

#3 Code Compliance Models

Code compliance models are big part of what we do at Cyclone. We have worked on many code compliance models across the nation. In general, energy models are an alternative to ComCheck compliance, which means you can use energy models to get building permits if you cannot pass prescriptively through ComCheck. With high-percentage glass buildings or buildings where you need to trade-off between lighting and enclosures to demonstrate compliance, energy modeling is the only option. Generally, you have to use an energy model if your building design has more than 40% window-to-wall ratio and/or your envelope or lighting power density doesn’t prescriptively comply with code.

In most states, code compliance is regulated by International Energy Conservation Code (IECC) or ASHRAE 90.1. In IECC section 401, it states that IECC is equivalent to ASHRAE 90.1 (IECC 2009 to ASHRAE 90.1-2007, IECC 2012 to ASHRAE 90.-1-2010, IECC 2015 to ASHRAE 90.1-2013). Most of our code compliance models are done to ASHRAE Standard 90.1. California has its own energy code called “Title 24”. It is very different from ASHRAE 90.1, but the principle of modeling is similar.

The code compliance ruleset is defined in ASHRAE 90.1, Chapter 11. It is called Energy Cost Budget (ECB) method. The ruleset of LEED models is defined by ASHRAE 90.1 Appendix G, which is called performance rating method (PRM). While the principles of ECB and PRM are very similar, there are differences – especially the way of establishing baseline systems. So, if you have a building that wants to pursue LEED and permit both, then the energy modeler has to build two separate baseline models.  There are some cities that require the use of PRM for code compliance but that is rare.

Michael Rosenberg from Pacific Northwest National Laboratory introduced a new way of modeling code compliance, which calls for a fixed baseline method.

The first change is to use PRM for code compliance models. The second change is to establish a fixed baseline at 90.1-2004 level.

It is very likely that this method will be implemented in the next few years and I think it will greatly reshape the way we model and the modeling software we use.

#4 Energy Modeling: LEED and Version 4

LEED Version 2009 is almost a past tense now and Version 4 (v4) is gradually becoming the new normal. Whenever changes take place in a long-established system, there is always some confusion and frustration.

For energy modeling, the main change is referencing code changes from ASHRAE 90.1-2007 Appendix G to ASHRAE 90.1-2010 Appendix G. HVAC efficiencies are higher, lighting power density allowances are lower, envelopes in baseline are more stringent and most importantly, daylighting controls are required now.

Taylor Roberts, from Group14 Engineering addressed some of the issues during his presentation.

Personally, I see the requirements of daylighting as the biggest challenge. ASHRAE 90.1-2010 does not address photocell locations and illuminance setpoints. Also, lighting zones and thermal zones that we typically model are not the same thing. The conflict between those two needs to be addressed through practice.

USGBC will definitely give interpretations on those issues and we will also address those here at Cyclone. Please follow our blog posts for future interpretations.

#5 Modeler Influence on Simulation Results

This is a very interesting topic. As an energy modeler, I believe very much that energy modelers have significant influence on simulation results. Pamela Berkeley, from Rochester Institute of Technology, gave a very detailed presentation on this topic.

I took a few facts from her presentation and used them to illustrate how we at Cyclone Energy influence our models:

  • What modeling software do you use?

Cyclone uses IES<VE>, which I personally think is the best commercial software on market.

  • Do you create a detailed model?

Cyclone develops highly detailed energy models. We believe detailed models give more accurate estimates and allows us to evaluate more elements of a building.

  • How you develop geometries?

Cyclone develops all geometry from measurements taken from drawings. Dimensions, components, shades, spaces, and etc. are also extracted from the drawings. We don’t import from BIM models as often those models are overly complex and take longer to clean up than it takes to create from scratch. Additionally, when you create a model rather than import you think about how all spaces are used and you have been control over the variables.

  • How do you model lighting and HVAC?

We model lighting per the design on the electrical drawings. We count lighting fixtures and calculate lighting power densities for each space and implement whatever lighting control is specified on the drawing. We either use lighting schedule as defined by the client or in the absence of information, use schedule out of ASHRAE 90.1.

We model HVAC systems per the mechanical drawings. Equipment sizes, efficiencies, zoning and schedules are according the equipment selections and sequence of operations.

  • How do you model receptacle loads?

Most times, receptacle loads are not defined by design drawings. If they are unknown, we use ASHRAE 90.1 and Fundamentals Handbook receptacle loads per space type.

As you can see, there are so many factors that need to be taken into consideration when developing an energy model. Different energy modelers modeling the same building can easily produce different results. It is not a black or white process, there is an art to it that influences the results.

I personally believe, energy modeling is never an easy task. It requires the energy modeler to have multiple areas of knowledge and capability of seeing buildings as whole. Great patience is required to start models from scratch and finish them with high-quality results.

If you have any questions about energy modeling, please don’t hesitate to contact us at workwithus@cyclone.energy. We can help!