Lowering energy use, elevating building performance
- Understand and reconsider the definition of high-performance buildings.
- Learn the two-step approach to net-zero: reduce, then produce.
- Understand total occupant comfort.
The National Renewable Energy Laboratory’s (NREL) definition of a net-zero building is a building that generates enough renewable energy on-site to equal or exceed its annual energy use. Net-zero energy design is a reality. We can achieve it today without the need for futuristic technologies. The questions we should be asking ourselves are: Is net-zero enough? Is net-zero the end goal? How does the pursuit of net-zero design impact the overall performance of the built environment?
According to Architecture 2030, nonresidential buildings consume 47.6% of all energy used in the United States annually. The sheer volume of energy consumed by buildings is one of the biggest, if not the biggest, contributor to carbon emissions and global warming, and that is only going to increase.
Design industry leaders, including ASHRAE and AIA, have established clearly defined goals for achieving net-zero design by 2030. The aim of ASHRAE Standard 189.1: Standard for the Design of High-Performance, Green Buildings is to provide an iterative road map toward achieving net-zero design by the year 2030.
A critical step on the path to net-zero design is ensuring that engineers and architects reduce the energy use of the building while elevating environmental performance as it relates to the overall health and comfort of occupants. This two-pronged approach to high-performance building design can lessen energy consumption and increase productivity. Ultimately, buildings can be positioned as a key component of the solution toward decreasing emissions and improving the environment.
High-performance: A new definition
Net-zero energy design is an iterative and collaborative process. Setting clear expectations within an integrated project delivery (IPD) team is important. An integrated team consisting of the owner, architect, engineer, contractor, and all vested partners must have a clear understanding of how the building will be designed, built, and operated with clearly outlined high-performance goals. High-performance environments should be the ultimate aim for design teams.
Perhaps it’s time to redefine high-performance. DLR Group believes high-performance buildings should be net-zero (or net-zero capable) buildings that maximize occupant comfort and productivity.
This vision of a high-performance building requires the traditional design process to evolve. A more integrative and holistic process with a focus on early decisions in the design phase and rigorous performance simulation is necessary. Building performance simulation and energy analyses are vital to establish indoor environmental and energy optimization criteria. Also important is a clear understanding of the anticipated use of building spaces to fully inform the design. An initial visioning session must establish measurable high-performance goals based on the building’s anticipated operations protocol.
Project energy budgets now take on as much significance as project cost budgets. Establishing energy and budget targets early in the design, and then tying systems analysis and evaluation to both project cost and energy budgets are critical to ensuring the project stays on track for energy consumption goals within the financial budget.
Synergies between engineered systems must be evaluated and presented to key stakeholders as part of a holistic analysis. At this time it’s essential to share projected energy and operational savings along with first costs to illustrate the positive impact on occupant comfort, and the total cost of ownership (TCO) of the building. If a building owner is to invest in a high-performance glazing system, then the associated reduction in chiller and boiler plant size, and the associated energy and maintenance cost reductions must also be presented as a TCO comparison.
Yet we don’t want to design bunkers. We want compelling, beautiful buildings that elevate the human experience through design.
Two consistent challenges must be overcome to produce buildings that achieve our new vision of high-performance design:
- An emphasis on value engineering to lessen first costs versus operating costs
- Thoughtfully considering occupant comfort and productivity through the entire design process.
A building’s initial capital costs and operational costs are often derived from different funding sources. This can pose a significant challenge in pursuit of high-performance if value engineering and minimizing first costs becomes the primary driver of the design process. Acquiescing to investor and/or owner demands to lower first costs during design can have negative long-term impact on occupant comfort and productivity. This does not have to be the case any longer.
The Research Support Facility at the National Renewable Energy Laboratory, Golden, Colo., is a 360,000-sq-ft office building that generates as much electricity as it uses. It uses rooftop photovoltaics for on-site production and was built for the same price as a traditional Class A office building. NREL’s “Controlling Capital Costs in High-performance Office Buildings: A Review of Best Practices for Overcoming Cost Barriers” white paper further documents that it is feasible to design and construct buildings that can achieve net-zero energy goals with standard first cost considerations.
A holistic, value-based building performance analysis is key to any net-zero design project. As part of performance analysis the design team must be disciplined, maintain focus, and champion the importance of elevating energy performance to the level of schedule and budget for the project. This ensures that both energy goals and budget priorities are managed and optimized throughout the design process rather than addressed in individual value engineering exercises. When a clear business case for a high-performance design strategy has been presented to the project team through a quality performance analysis, it is much easier to retain that strategy during a traditional value engineering process.
The engineering team has learned that focusing purely on reducing energy consumption during design will not guarantee high performance. A focused reduction of energy consumption must go hand-in-hand with designing spaces to optimize occupant comfort.
A commitment to ensuring occupant comfort in the design process to produce a small increase in productivity can potentially offset annual operational costs during a building’s operational lifecycle. A user-friendly, high-performance building with healthier and happier occupants can provide opportunities to enhance the morale of employees, improve operations, return a premium for owners through increased rents, and ultimately reduce operating costs.
During a building’s lifecycle, its use changes and the needs and perception of occupants also change. A design that cannot bend and shape to evolving user needs cannot deliver a state of mind that expresses satisfaction with the surrounding environment.
When users are not comfortable, they take action to modify their environment. We see this every day. Personal space heaters seemingly appear overnight. Next are fans of all shapes and sizes. Then a power strip for that heater, the fan, and the needed mini-refrigerator. Perhaps some curtains or posterboard to block glare. A book or trash can might be placed over the diffuser. In the end, all of this extra equipment and modification alters system performance and ultimately energy use and performance.
Reduce, then produce to find net-zero
To achieve our goal of high-performance buildings, design teams must first address energy reduction strategies and then incorporate energy production using on-site renewables. First reduce, then produce.
The first step in high-performance building design, whether new construction or a deep energy retrofit of an existing building, is to engage in a holistic assessment of practical energy reduction strategies. This assessment includes building systems optimization, high-efficiency equipment, energy recovery, system synergies, an emphasis on plug load reduction, and passive energy reduction such as mixed-mode natural ventilation, thermal massing, and solar shading.
DLR Group’s “reduce, then produce” belief is grounded in a 75-25 approach. First, reduce the energy demand of a building by as much as 75% compared to baseline. Then invest in renewable energy production systems for the final 25% reduction to achieve net-zero. At a 75% energy reduction, the return on investment of the energy production system generating 25% of energy need becomes more practical.
Optimize building design for occupant comfort
The second element in our new definition of high-performance building is to ensure the optimization of a building’s indoor environment for the ultimate comfort of building users. DLR Group defines occupant comfort as “the state of mind that expresses satisfaction with the surrounding environment.” This also is the essence of design. As designers, our challenge is to balance both aims of high performance to maximize occupant comfort with zero-net energy consumption.
Optimization entails critical thinking about the impact of the human factor on design and how occupant use will impact performance. We must understand the client, the ultimate purpose for the space(s), the influence of plug loads, and other variables through design discovery to effectively understand the human factor. The aim is to ensure optimum occupant comfort.
Design for occupant comfort begins with holistic thinking about four key aspects: visual, thermal, air quality, and acoustical comfort. Balancing these elements within a net-zero energy environment can produce true high-performance design.
Visual comfort is critical in all spaces for a welcoming, productive environment. One of the essential design strategies for net-zero energy design is daylight harvesting. However, daylight harvesting without proper glare control can often negate the predicted energy savings. If occupants are uncomfortable due to glare or heat gain, they will take control of their environment by blocking the daylight that induces glare. Daylight induced glare is subjective based on the direction of view and angle at which daylight luminance reaches the task surface.
For example, Fireside Elementary School, Phoenix, is designed to reach net-zero. The design team controlled glare by choosing different visible light transmittance glazing with customized window shading solutions for different orientations. The daylight harvesting strategy included a simple control system. Light switches were offered with three options: auto on, off, and an audio/visual setting. The auto on button does not turn on all light fixtures. A photocell takes into account the amount of daylight and only turns on required light fixtures.
Designers can evaluate daylight simulation models to understand harvesting potential. Again, the collaboration of an integrated design team allows interior designers to clearly understand the assumptions for surface reflectance values within a space. When interior designers select paint colors and surface finishes, these can be chosen to maximize the daylight harvesting potential of the design.
In addition to the quantitative analysis, it is important to access qualitatively the scenarios when glare may be an issue, especially due to direct sun. This is when the interior blinds will be used, and some modeling may fail to capture the impact of these shading features on the daylight.
In another case, at Google’s Kirkland, Wash., campus, designers recently maximized the daylight zones as part of a major tenant improvement. The design provided interior glazed partitions, which increased the number of spaces with a view and extended access to daylight for additional spaces.
Thermal comfort of occupants, more than any other criteria, can have a high potential to optimize energy use. Several factors impact thermal discomfort in a space. These include metabolic rate, clothing, mean radiant temperature, relative humidity, air temperature, and air speed.
ASHREA Standard 55 specifies conditions for acceptable thermal environments. However, regardless of the air temperature, the reality is if occupants perceive increased radiant heat or heat loss within their space, such as from an exterior glass wall, their first instincts are to turn on the fan or space heater, or reach for and alter the thermostat. Over time, the adverse impact of this behavior on energy use is significant.
At Fireside Elementary School, this behavior was mitigated by providing a thermal mass wall that provides a lag in the heat transfer and, most importantly, by optimizing view glass with shading. This helps in avoiding direct solar radiation and in maintaining a comfortable operative temperature.
Indoor air quality (IAQ) impacts energy consumption and plays a crucial role in occupant health. Indoor pollutants can be diluted by bringing in fresh air from outside. However, depending on the building type and climate, filtration of outdoor air can prove to be energy-intensive. The greater the volume of air and the more filtration required for this outdoor air, the more energy will be required to condition it.
A common strategy that high-performance buildings employ is demand-control ventilation. Based on changes in occupant density within a space, carbon dioxide levels can be measured and the amount of outdoor air required can be controlled. However, this strategy is often executed poorly in buildings. Due to poorly implemented sequences of operations or sensor calibration issues, it’s common for outdoor air to be completely eliminated during occupied hours based on the CO2 levels. This increases indoor pollutants, such as volatile organic compounds (VOCs) emanating from finishes, which can negatively impact air quality. The role of an integrated design team, including the mechanical engineer and/or control system integrator, is to clearly communicate a sequence of operations for the HVAC controls and establish adequate sensor calibration procedures to ensure air quality. Diligent commissioning or retro-commissioning can also address and enhance IAQ.
At the Google Kirkland Campus, the mechanical system selection was based on system performance in regard to IAQ to optimize comfort in addition to energy efficiency. A number of mechanical systems were modeled and evaluated as part of a mechanical decision-making matrix. Competing systems were evaluated for energy performance as well as the client’s goals of thermal comfort, acoustics, IAQ, and the total impact on lifecycle costs. For this reason, a 100% outside air system with chilled beams was selected to meet all of the criteria.
Acoustic comfort can be achieved by controlling noise at the source; this is a key strategy especially with HVAC-induced background noise. Early input on acoustical issues, particularly around key adjacencies, can aid in avoiding costly and energy-consuming acoustical interventions. Proper isolation of HVAC to minimize noise requires careful planning on equipment selection, ductwork layout, and air distribution system design. Value engineering can have a significant impact on noise control when sound attenuators, duct runs, and HVAC equipment with similar efficiencies but varying noise levels are debated. More attenuation and longer duct runs with extra fittings result in greater pressure loss. This requires more energy to power fans, more noise to push the air, and the deterioration of acoustical comfort.
Tracking building performance
The true measure of high performance is assessed over the operational life of the building, not just at the moment the project is handed over to the owner. It is vital to understand that high-performance building designs don’t necessarily produce high-performance buildings without correct operations and maintenance procedures.
Evaluating the actual performance of a building design post-occupancy is vital. Without post-occupancy evaluation, it is impossible to know if a building is performing—both operationally and programmatically—as designed and if the client is, in fact, receiving a valuable return on investment.
As design professionals, the best course of action is to ensure post-occupancy evaluation of building operations and program performance are part of the standard design services or that this scope is included in the commissioning process.
A measurement and verification (M&V) process adhering to guidelines set forth by the International Performance Measurement and Verification Protocol (IPMVP) should be standard practice for all high-performance building projects. Designers also can use the energy model as an operational target throughout the first year of operation. Tracking against the model will help set the building on a track for high-performance. The predicted building systems energy use from the design energy model should be verified and updated post-occupancy with actual energy breakdowns for each building system.
Tracking energy consumption and peak demand can be as simple as collecting utility bills for at least 12 consecutive months of operation. In a high-performance building, a detailed breakdown of energy use for each major energy-consuming system is needed to track ongoing building performance. This data can be harvested through utility meters and system submeters, building automation data trend analysis, or with portable data-logging devices. At a minimum, submetering key energy end-use systems to match the predicted energy consumption breakdown for loads including cooling, heating, fans, pumps, lighting, plug loads, and domestic hot water systems will enable a thorough M&V process. Commissioning the submeters to confirm that they are designed, installed, and calibrated to operate as intended is critical to ensure high-integrity data is being harvested for analysis.
Assessing occupant comfort can be accomplished in several ways. Most often, you will hear about issues within the first year during a typical warranty period. However, a more detailed post-occupancy evaluation can reveal occupant related challenges. Regular surveying of occupants is often the best method to gauge occupant satisfaction and establish baselines for future measurement.
The next big step toward ongoing tracking of building performance is real-time monitoring. This is a continuous optimization process that tracks both energy consumption and occupant comfort patterns.
Energy tracking, benchmarking, and disclosure are becoming a mandatory procedure across many of the nation’s major metropolitan areas including New York City, Chicago, and San Francisco. For committed owners, a net-zero energy focused building certification such as ASHRAE’s Building Energy Quotient (bEQ) may prove to be beneficial to reinforce and communicate their commitment to tracking, measuring, and verifying building performance.
The high-performance future
High-performance buildings must achieve net-zero energy consumption and maintain superior occupant comfort. These principles, and a design process to produce a net-zero energy design with a focus on occupant comfort, can be applied to both new construction and the renovation of existing buildings.
Today, most of the focus for net-zero buildings is directed at new construction, which constitutes a small portion of the total energy usage in the built environment. Upgrading the existing building stock provides an even bigger opportunity to reduce carbon emissions for positive climate change. A Lawrence Berkeley National Laboratory study found median whole-building energy savings of 16% for existing buildings and 13% for new construction through commissioning. Potentially, this means that for every seven buildings that are retro-commissioned, we are essentially offsetting the energy use and cost of a similar-sized building.
A study by the National Renewable Energy Laboratory found there is technical potential for more than 47% of existing commercial building floor space to achieve net-zero energy using currently known technologies and design processes.
Above all, design engineers and building performance analysts can play a significant role in achieving the industry goals for net-zero energy while elevating the indoor environmental quality and the health, well-being, and productivity of building occupants.
Ruairi M. Barnwell leads DLR Group’s Building Optimization practice and contributes his high-performance building design expertise on design teams in the firm’s core market sectors. He was a 2013 40 Under 40 award winner. Premnath Sundharam is a Certified Energy Manager and a certified Building Energy Modeling Professional. Premnath is an expert resource for energy modeling and sustainable design at DLR Group.