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Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal. [ABSTRACT FROM AUTHOR]

As the United States continues its progress toward sustainable construction, net zero building design is becoming an increasingly important and popular topic. Two definitions of net zero energy performance, monthly and annual, provide different levels of energy autonomy and efficiency within a building. This article analyzes the viability and incremental cost for two-, three-, and four-story multifamily apartment buildings to reach both annual and monthly net zero energy performance throughout four climate zones in the United States using baseline reference buildings that represent current construction practices. Building size plays a large role in determining the capability for a building model to reach annual or monthly net zero. Two-story buildings are capable of reaching annual net zero with an increase in construction cost of about 4.4–5.6%. Three-story buildings in warmer climates can achieve annual net zero with an increase of about 5.1%, but models in colder climates cannot reach annual net zero performance. Four-story buildings cannot achieve net zero, owing to insufficient building area for solar arrays to produce electricity. Monthly net zero energy performance was significantly harder to achieve, with the only case reaching this goal being the two-story Houston based model, at an added cost of 8.2%. Generally speaking, only small buildings in warm climates will be able to achieve monthly net zero without vastly oversizing photovoltaic systems and increasing costs without adequate payback. [ABSTRACT FROM AUTHOR]

Bayesian and nonlinear least-squares methods of calibration were evaluated and compared for gray-box modeling of a retail building. Gray-box model calibration is one form of system identification and is examined here with perturbations to the simple yet popular European Committee for Standardization (CEN)-ISO thermal network model. The primary objective was to understand whether the computational expense of probabilistic Bayesian techniques is required to provide robustness to signal noise, specifically with regard to lower dimensional problems (physical or semiphysical), where model calibration is preferred over uncertainty quantification. The Bayesian approach allows parameter interactions and trade-offs to be revealed, one form of sensitivity analysis, but its full power for uncertainty quantification cannot be harnessed with gray-box or other simplified models. Surrogate data from a detailed building energy simulation program were used to ensure command over latent variables, whereas a range of signal-to-noise and noise colors were considered in the experimental study. The fidelity to the building zone temperature and thermal load was the basis for comparing results. Utilization of uniform priors showed that both methods performed similarly well. Bayesian calibration outperformed traditional methods on noisy data sets; however, traditional methods were adequate up to an approximately 25% noise level. The thermal gray-box model calibration has the intended application of embedded model predictive control, where speed, accuracy, and robustness are crucial. Traditional methods required approximately 100 times less CPU time and are recommended given the model simplicity, application, and expected system noise levels. [ABSTRACT FROM AUTHOR]

Sustainable design should be applied in all phases of the life cycle of a building, including programming, design, building construction, building operation, and finally demolition. This paper compares and contrasts sustainable design programs based on the life cycle of a building in North America, Europe, and Asia. Tables comparing programs from these three regions are provided for each phase in the life cycle of a building. These tables can be used by building design professionals as a reference guide to sustainable design around the world. The tables also highlight specific requirements or concerns that are applicable in a particular region. The similarities between different programs and regions can be taken into consideration during the planning of sustainable design work, regardless of the region of construction. Finally, references to more detailed program documents are provided so that interested readers can determine specific requirements that apply in a region of interest. [ABSTRACT FROM AUTHOR]

This paper describes an investigation of the economic performance of a central chiller plant with thermal energy storage (TES) operating in a hotel in California and an office building in Wisconsin for the following three conventional control strategies: chiller-priority, constant-proportion, and storage-priority control. Since all control strategies depend on properly selected design parameters, the storage and chiller capacities as the primary design parameters were varied over a wide range, and the life-cycle economic feasibility of each possible design was assessed over a 20-year economic life using the net present value method. Measured cooling and weather data for both buildings were used in annual calculations to determine annual utility cost savings on the basis of one of four artificial rate structures. Trends in the life-cycle economic performance of TES systems as a function of chiller and storage capacities were revealed, and design guidelines were developed. [ABSTRACT FROM AUTHOR]

This paper describes a macroanalytic approach to energy management in buildings. Conventionally, energy improvement measures are designed and deployed in buildings, expecting and typically achieving energy savings from changes to the building envelope or energy systems such as lighting system retrofits. However, additional savings opportunities can be identified by analyzing the interaction between building systems and the influence of building occupants. An energy accounting system can provide the required wealth of data and information and facilitate the analysis on which to design and refine further retrofit measures. The problem of energy management is cast in the framework of a classical feedback control loop: A “sensor” (energy accounting system) monitors the utility consumption of the building in question, compares it with predefined “setpoints” (energy consumption targets) and analyzes the deviations within a comprehensive reporting system (the “controller”). In response to the analysis, adequate measures including occupant motivation are defined by the controller and applied by the “actuator” to the “system,” embracing the building and its occupant under the prevailing weather conditions. The system output is the actual energy and utility consumption that is compared with the target values, and the loop is closed. The paper discusses an implementation of an energy management system that has been applied successfully to the measurement and verification of utility cost savings in an energy savings performance contract in Germany. Building occupant motivation—a category of energy retrofit measures that is often overlooked—is presented. A set of tabular and graphical data illustration and analysis techniques is presented along with recommendations for building occupant motivation measures and associated implementation guidelines. [ABSTRACT FROM AUTHOR]

High-performance buildings, such as zero-energy buildings (ZEBs), are an important step toward a reduction in greenhouse-gas emissions. Because ZEBs may exhibit large differences between demand and on-site generated electricity, residual electrical loads imposed by the building may fluctuate between positive and negative values. Furthermore, such buildings can be characterized by large temporal changes in residual load, commonly caused by clouds passing on a sunny day. Today, electricity grid operators can easily deal with a single ZEB with this behavior. But what happens if large portfolios of ZEBs have the same behavior? In this study, a highly efficient office building with a total floor area of 8,355 m2 located in Denver, Colorado, was designed and simulated using a detailed building energy modeling approach. Combining the building energy model with a photovoltaic model showed that the building reached net positive status on an annual basis. Further analysis of residual loads and strategies for their reduction revealed the limited potential of demand-side management in ZEBs and the high flexibility of batteries. Using a multiple-objective optimization approach for optimizing several simplified electric and thermal storage systems allowed the comparison of different strategies for residual load reduction. Although electrical storage may not yet be economical given today's system costs, results show that the residual loads can be effectively managed and reduced, and at the same time, an increase in photovoltaic self-consumption can be achieved. The analysis concludes with the presentation of a multiple-objective optimal solution (Pareto front) for a battery storage model, indicating what utility incentives would be required to achieve cost-effectiveness for a range of price scenarios for battery systems. [ABSTRACT FROM AUTHOR]

Low delta T syndrome, that is, the operation at low differences between supply and return chilled-water temperatures, increases the energy consumption of chilled-water systems. Numerous causes of low delta T lie at the cooling coils. As the load on the coil increases, more chilled water is sent through it. A point of saturation is reached when significant increases in chilled-water flow result in negligible increases in provided cooling power. The ability to recognize when such saturation is occurring and restrict flow in such situations is needed to combat low delta T. An intelligent pressure independent control valve attempts this by measuring and logging inlet and outlet water temperatures and water flow rates. Through nonlinear regression of measured coil data, a novel approach for the valve to predict saturation was developed and tested. The resulting curve fit was then used to predict whether a coil was operating in a constant- or variable-air-volume system. In total, 128 test coils over four climates and various system characteristics showed a 79.7% correct prediction rate. [ABSTRACT FROM AUTHOR]