Specifying systems to achieve outcome-based energy goals
The design of energy-efficient building systems requires a holistic, integrated design process, with early engagement, supported by three basic elements for success
- Understand external drivers for design at multiple community scales, including three key factors in developing and measuring system goals.
- Explore five emerging trends to impact energy goals and to navigate the increased momentum toward net zero design.
- Learn how to use a front-loaded goal setting process to achieve successful, cost-effective and timely outcomes.
In 2020 the world faced disruptive change, bringing into focus a plethora of drivers for building design, from indoor air quality to
resilience to climate change. A building system — whether lighting, building envelope or heating, ventilation and air conditioning — must perform as part of a whole-building approach to achieve maximum performance, including efficient resource use.
The key to a successful energy-efficiency project is early stakeholder engagement, which identifies key priorities that drive a roadmap for design, construction and operations. The industry has benefited from a variety of frameworks, from energy standards to design guides to green building rating systems like U.S. Green Building Council’s LEED, Green Globes and the Living Building Challenge.
No one system alone may suit the needs of a project’s stakeholder group. In the virtual world we’ve experienced the past year, we have benefited from increasing our engagement with broader stakeholder groups and using virtual big rooms. The big room concept is derived from lean construction practices, where stakeholders are brought together early in a project phase to build rapport, share knowledge and collectively reach consensus on key decisions.
Drivers for system design
Early engagement with all stakeholders should identify both qualitative (beauty, biophilic design, collaboration) and quantitative drivers for design to explore regional or local sustainability initiatives or mandates. In Washington, D.C., starting in January 2021, a new building energy performance standard went into effect. This standard requires a portion of buildings that perform below the city’s median source energy use intensity or Energy Star score to reduce its energy use by 20% over a five-year period. This cycle is repeated an additional three times, eventually impacting buildings down to 10,000 square feet in size.
BEPS complements the district’s energy code, set to ratchet up stringency in parallel. This outcome-based approach is a significant evolution from frameworks that credit efficiency based on predicted performance using whole building energy analysis.
Beyond energy efficiency alone, sustainability considerations transcend regional boundaries and have become integral to nearly all programs and frameworks for measuring outcomes. The United Nations’ Sustainable Development goals bring into clarity 17 topics of focus, all of which relate to building systems, with goals of Good Health and Well-Being (3), Clean Water and Sanitation (6), Affordable and Clean Energy (7), Industry, Innovation and Infrastructure (9), Sustainable Cities (11) and Responsible Consumption and Production (12), most directly related to the role of a consulting engineer in developing implementable solutions across a range of scales.
The consulting engineer impacts outcomes for eco-systems both on Land and Water (14, 15) and relies heavily on the power of knowledge sharing across generations through mentoring, apprenticeship and Education (4). Stakeholder engagement, so beneficial to integrated design, rests on a foundation described by Peace, Justice and Strong Institutions (16) and Partnerships for the Goals (17).
Three key factors to achieving outcome-based goals
Beyond the integral sustainability goals, three other factors are key to achieving the system goals. They include: integrated design thinking, building performance analysis and life cycle cost analysis.
- Integrated design thinking
With the accelerated focus on net zero energy buildings, the demand for integrated design thinking is greater than ever. Innovation has brought the world incredible technology, but sometimes at the expense of beauty. The judge of a successful project is not performance alone, but the user’s perception of the environment: Is innovation up front and center or not immediately noticeable, like elements of the natural world?
A sign of integrated design thinking occurred several years ago when the American Institute of Architects began to evolve its criteria for design excellence. No longer are the Top Ten Measures of the Committee on the Environment a separate program, but are now the AIA’s primary measures for design excellence — a clear and resonant stance that sustainability is not a separate measure to consider, but is a part of the greater ecosystem.
Perhaps this is why we see a significant amount of biophilic design influence on recent projects. Biophilic design goes beyond material selection and draws on systems thinking of the natural world to shape building design. Engineered systems play a big role in the control of airflow, views, light, comfort and other sensory perceptions. The tree serves as an inspiring reminder of what nature achieves, pumping water from the ground to a tree’s canopy, to its structural strength, to its ability to sequester carbon.
- Building performance analysis
Once the context and goals for an integrated design project are set, iterative design exploration takes place. Building performance analysis has now become accessible to a wider group of stakeholders due to advancements in cloud-based technology and intuitive user interfaces.
It is important to align the right tools and workflows with the right skillset at the right time. ASHRAE Standard 209: Energy Simulation-Aided Design and the AIA Architect’s Guide to Building Performance provide timely guidance. One of the most powerful uses of early design phase modeling is education and engagement. The team’s focus should not be on determining an exact energy outcome, but using data collection of thousands of a building’s inputs to drive more dialogue between the design team and the building’s user and operations team. These discussions allow greater potential for right-sizing a building’s systems for a user’s actual needs. Sensitivity analysis allows the team to focus on opportunities with the highest impact and opportunities for cost-shifting.
A building’s energy use intensity has traditionally been used as a measure of efficiency. However, thermal load efficiency management allows building systems to reduce in size, with impacts on building area efficiency, structural systems, electrical and gas infrastructure and corresponding first cost. Flattening the load profile of a building through passive measures is not a new concept, but can be tested more rapidly than ever before. A potential opportunity is the continued demand for high-quality first cost data for what can often be very granular energy conservation measures, not necessarily fully detailed early in a project’s design process.
Energy analysis is only as good as a team’s understanding of inputs, which can be challenging for complex buildings. Significant variables may include building enclosure performance, process loads or occupancy. Utility rate structures are often simplified for energy analysis, but can result in a significant deviation in outcomes, especially if a utility rate structure includes significant demand charges, such as in New York City.
Several energy frameworks use different metrics for determining performance: ASHRAE 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings (energy cost), International Green Construction Code (source energy and greenhouse gases), city metrics (mixed from Energy Star to Zero Energy Performance Index). The LEED rating system was the first major framework to use a differential framework from a baseline.
The baseline is complex in itself, floating based on a building’s size and other basic characteristics. The opportunity is now for a forward-looking approach to modeling: meet prescriptive requirements and then optimize to achieve the most cost-effect bundle of energy conservation measures.
But what happens if utility costs in a locality are low? On recent work for the school system in the U.S. Virgin Islands, the DLR Group team experienced a significant impact on decision making with an average electricity rate of $0.40/kWh compared to a commercial average of $0.11/kWh for the United States as a whole.
For regions of the country with low utility rates, many energy conservation measures can experience long financial payback periods. To address this, many companies already use carbon pricing to drive internal business decision-making, including energy companies. Carbon pricing, also referred to as shadow carbon pricing or societal value of carbon pricing assigns a value to emissions per metric ton equivalent. On a recent project, the DLR Group team used a college’s value of $50/ton, essentially doubling the effective utility cost of natural gas.
- Lifecycle cost analysis
Many owners, particularly with public institutions, mandate life cycle cost analysis, with a traditional emphasis on HVAC systems. Selection options to study should involve early dialogue with an owner’s team, including key facility management staff. It is important to select options without initial first cost prejudice, but rather that address a range of the owner’s values.
On a recent project, DLR Group identified that energy was important, but less of a priority than factors like maintainability, support of the building’s program and a very specific element of indoor environmental quality: acoustics. The systems selected should be options that the design team would not have major concerns with implementing. Innovation carries some inherent form of risk: a well-thought-out process allows an owner’s team to react to a range of options on the risk spectrum that highlights opportunities and concerns that transcend more than a single option.
Life cycle cost analysis options may have large differences or may be studies of smaller permutations on a scheme. An owner team may find focused study more insightful or even realistic if the owner already has significant facility management experience with a particular type of system or technology.
- Variable refrigerant flow system with dedicated outdoor air system.
- Variable air volume system with air-cooled chiller and natural gas condensing boiler central plant.
- Ground-source heat pump system with dedicated outdoor air system.
- Example 1: Optimization of air-handling unit pressure drop: trade-off of face velocity versus equipment size.
- Example 2: Consistent space cooling and heating with variations in central plant
- Air-cooled scroll chiller with primary-secondary pumping.
- Air-cooled screw chiller with variable primary pump.
- Water-cooled centrifugal chiller with forced-draft cooling tower.
Designing for the future
An increasing focus on net zero energy buildings supports themes of resilience, both in terms of short-term vulnerabilities to power outages for example, as well as the long-term mitigation of extreme climate. Datasets now simulate impacts on a building’s system with forecast climate data with 50- and 100-year outlooks, similar to the traditional availability of flood potential data for 100- and 500-year storm events. The themes below represent emerging trends of what consulting engineers will help owners and communities navigate over the next decade.
Electrification: Even 10 years ago, in colder U.S. climates, the concept of shifting heating energy use to electricity from natural gas was not commonly discussed. Yet, to reduce dependency on fossil fuels, an acceleration of adoption of electricity has taken off:
- Service water heating: Air-to-water heat pumps have been more accessible to the residential market and are now seeing additional development for the commercial market.
- Air-source heat pumps: There is a significant increase in the use of variable refrigerant volume/flow systems due to advances in technology that reduce derating at low ambient temperatures. A holistic analysis of these systems is needed though, given their use of R-410a, which has significant global warming potential.
- Heat recovery systems: Ground-source heating and cooling has been a common system used in many high-performance buildings, now with an increasing focus on larger centralized systems where heating and cooling energy shifts can be achieved across a larger diversity of building types. These systems use traditional chiller technology to recover condenser heat for direct use, before even transferring this heat to a geo-exchange loop.
Replacement: The industry has traditionally relied on data from ASHRAE to determine standard equipment design life. Equipment is often not replaced, and is instead repaired or rehabilitated. Increasing care should be applied to end of equipment life.
- How will the equipment be removed? Is there an elevator or easy roof access?
- How will components be recycled? Can they be repurposed?
- Are components easy to repair or is there the potential for parts obsolescence?
- Can a piece of equipment be refurbished in place, reducing related transportation and construction energy?
Building automation: The industry is seeing increasing awareness and reference to ASHRAE standards for building automation systems, not only an open-protocol standard like BACnet, but also sequences of operation. The translation of a design engineer’s sequence intent into an automation system is a critical, but often discontinuous step, as underlying code is not easily checked. Setting up a system with enough foresight for fault diagnostics and detection platforms supports not only an initial system’s commissioning, but also ongoing optimization.
Real-time trend analysis is increasingly critical to verifying a system is operating properly. Even if a space is meeting comfort criteria, it may be doing so inefficiently through excessive pump/fan energy or through simultaneous heating and cooling. More frequently, building owners are offering building data as a means of communicating energy information and air quality to their occupants.
Digital twins: Large-portfolio clients use facility condition assessments to ascertain a facility’s condition index, a measure of deferred maintenance compared to the current replacement value. These assessments are often performed every five to 10 years, but often without a data exchange framework that allows facility management, energy management and education to be interlinked together. A digital twin can integrate a computerized maintenance management system that benefits a wide range of stakeholders, from design professionals to end users to facility managers.
Resiliency: Like sustainability, building resilience now encompasses a wide range of topics, at many scales. For building system, some key elements to focus on include:
- Vulnerabilities are location-driven: A building is located below a flood plain or has a structural system designed only to winds of a Category 3 hurricane.
- Hazards: high winds, extreme temperature, flooding.
- Criticality — necessity for continuity of operations or rapid restoration of operations.
The upcoming decade presents significant opportunities for consulting engineers to address challenges of scale, while augmenting partnerships between owners, design professionals, contractors and other allied professionals. Technology and automation will continue to be a backbone of innovation, but with the partnerships that only come from multidisciplinary collaboration.
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