Sights on 2030: Early-Stage Energy Modeling for High-Impact Results

| November 8, 2016

by Ian Robinson and Victoria Rybl

Architecture 2030’s “2030 Challenge”has laid out an ambitious target of achieving net-zero operating carbon emissions in all new buildings and major renovations by the year 2030. Lofty initiatives relating to climate change are nothing new to the building industry. However, as initiatives like the 2030 Challenge achieve widespread adoption by code officials, compliance with such targets is bringing about radical changes in the design process. Critical, early-stage design decisions such as building form, envelope properties, and HVAC system selection can no longer be made without assessing their energy impact. The imperative to design ever-more-efficient buildings has made it crucial to engage energy modelers as part of the design teams very early in the process.

Defining success : “How good is good enough?”

Deciding what metrics to use and what performance target to design is the first step in any energy-informed design process. Both the metric and the target will be unique to the project. LEED (and often building owners) require energy cost as a metric. The Massachusetts Stretch Code uses site or source energy consumption. The 2030 Challenge uses net greenhouse gas emissions. Optimizing for one metric or another can lead to vastly different design decisions. Which metrics are most relevant to a given project and what the targeted performance should be is determined by what hurdles that specific project needs to clear. However, thoughtfully choosing a metric and striving towards a target is fundamental. Establishing the target early in the process and defining that target as a design requirement will help ensure all parties are focusing their efforts on a desired end result.

Value-add modeling in early design: “Now what?”

Energy modelers often struggle to produce meaningful results in early-stage modeling due to the absence of concrete details. It is exceedingly difficult (and time-consuming) to produce model after model while major design elements are in flux. However, with well-documented assumptions and modern energy modeling tools, it is possible to make valid determinations and guide the design team towards positive outcomes. Issues that have the most impact include:

  • Massing options.
  • Glazing and envelope options.
  • HVAC systems.
  • Targets for internal gains (occupancy, lighting, plug loads).

As if optimizing each component individually weren’t complex enough, design decisions regarding each separate item can also impact the optimal choice for each of the others. At this stage, it is important to simplify the model and use time-efficient tools to minimize modeling time and allow a maximum number of energy modeling runs. With simplified models, the team can perform dozens, or even hundreds of simulations to yield a true sensitivity analysis for each design variable. Sensitivity analyses assess the impact of major design elements on energy performance in multiple scenarios. For instance, what impact does changing the average lighting power density have on building energy usage if the façade is well-insulated and the HVAC is a chilled-beam system? What if the building is lightly insulated and the HVAC is VAV? Frequently, the answer in one scenario is very different from the other.

By assessing design decisions holistically, we develop a more accurate picture of how each decision impacts the overall project. Using the outcomes of early stage modeling, the team can make decisions that optimize energy usage and first costs without any guesswork. Equipped with this knowledge, the design team can move into the detailed design stage with clear direction regarding energy performance. Owners and architects can have confidence that each individual piece of the puzzle will contribute to the bigger picture, meeting its energy-related goals.

 

Ian Robinson

Ian Robinson

Ian Robinson, PE, is an energy engineer and project manager at RDK Engineers.

Victoria Rybl

Victoria Rybl

Victoria Rybl is an energy engineer.

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Category: All, Green