Whole-building Energy Simulation Research Articles

Self-powered electrochromic smart window helps net-zero energy buildings

Net-zero energy buildings are becoming an important energy-saving and low-carbon technology for global environmental protection and resource conservation. As the least energy-efficient building components, windows have promoted the development of electrochemically light/thermal management, where smart windows without external electrical supplies are highly desired for net-zero energy buildings. Here, we develop a self-powered electrochromic smart window system to regulate solar radiation transmittance, constructed by a triboelectric nanogenerator (TENG) and a high-performance electrochromic device. The visible–near-infrared (VIS-NIR) dual-band electrochromic device is well-designed based on an eco-friendly low-energy demand phenothiazine redox ionic liquid, demonstrating a fast switching response of ﹤1.9 s, a large transmittance modulation of >51.8 %, and outstanding electrochemical durability (5.5 % attenuation after 4000 cycles). Upon continuous pressing/releasing motions, the integrated TENG-powered electrochromic smart window (TECSW) displays a prompt light/thermal management behavior with desirable privacy preservation performance (transmittance modulation of 51 % in the visible region) and excellent thermal management property (12.3 °C reducti°n). The whole-building energy simulations show that TECSW can save 347.79 MJ/m2yr (amounting to 96.60 kWh/m2yr) of operational Heating Ventilation Air Conditioning (HVAC) warming/cooling energy consumption among 34 cities in China, accounting for 17.25 % of the total energy consumption. This research provides new insight into designing green and energy-efficient smart windows for net-zero energy buildings.

A novel approach based on equivalent sky radiative temperature for quick computation of radiative cooling in building energy simulation

Passive radiative cooling materials (RCM) can cool surfaces by radiating heat to outer space via long-wave radiation. In simulation application, co-simulation of the thermal process between RCMs and building structures is generally required; however, the high computing time cost and low integration level have hindered the integrated whole-building simulation in architectural design. Traditional building energy simulations utilize the effective sky temperature to numerically approximate the effect of sky radiation. However, given the limitations of effective sky temperature concept, it is more suitable to evaluate diffusive gray surfaces while not fully capturing the characteristics of radiative heat transfer for spectrum-selective surfaces. In this study, an innovative equivalent-sky-radiative temperature was introduced as a new equivalent parameter to accurately simulate the thermal performance of RCMs in buildings. Embedding this new parameter into whole-building energy simulation tools such as EnergyPlus and DeST is expected to significantly improve the calculation accuracy and reduce the computational cost. Case studies in this work have shown an average error of 5.47 W/m2. The generation of the new parameter for 50 cities worldwide also demonstrated the technical feasibility of applying the equivalent-sky-radiative temperatures to evaluate the thermal performance and energy savings of real-world RCMs in buildings.

Techno-economic analysis to determine the potential of perovskite-based PV blinds for buildings

This paper analyses a novel perovskite-based Photovoltaic (PV) blind system for buildings. Some buildings are unable to install traditional solar systems because they cannot install PV panels on the roof or facade. Traditional PV materials have a long value chain, also the resulting solar panels are bulky and heavy and not suitable for blind applications. Recently, Perovskite crystals, a new semiconductor material, have shown potential for reducing the manufacturing cost while providing high energy conversion efficiency. However, a significant issue with PV blind systems is that they typically receive less solar radiation than traditional rooftop PV systems, resulting in less electricity generation, particularly when the PV blinds are used indoors behind the windows. In addition, unlike conventional rooftop PV panels, PV blind systems affect the total energy consumption in the building by changing the heating and cooling demands as well as interior lighting. Utilizing these new PV blind systems effectively necessitates a holistic analysis of solar potential, performance, and cost-effectiveness. In this study, whole-building energy simulation, techno-economical modeling, and parametric analysis will be used to compare perovskites PV blinds and conventional rooftop PV arrays.

Impacts of lighting and plug load variations on residential building energy consumption targeting zero energy building goals

Mitigating building energy use and carbon emissions in the buildings sector is a globally recognized goal. This is being pursued through the adoption of zero-energy building (ZEB) targets, with formal government regulations and policies actively embraced in domestic marketplaces. However, building assessment methods used for the ZEB certification system in South Korea have garnered substantial critique from building energy engineers and practitioners for their practical applicability. This study investigated energy consumption patterns of single-family residential buildings, focusing on two major energy end-use categories: lighting- and plug-loads. Empirical analyses and field measurement data were used to construct representative profiles of lighting and plug loads, as well as power density values, based on data from existing residential buildings. These distinct profiles of lighting and plug loads were used as input data for a residential ZEB evaluation. The measurement data from 60 detached houses in South Korea was utilized to derive four representative profiles for the category's loads. These profiles were subsequently employed for simulation-based analyses to assess load diversity. A whole-building energy simulation model was developed to conduct annual building energy analyses and assess ZEB certification based on the set and applied load profiles. Results showed that building energy consumption could vary by up to 23% based on different lighting load patterns and by as much as 58% for differing plug load patterns. These findings underline the importance of refining the current domestic ZEB certification process by considering the influence of diverse domestic load profiles on energy consumption and building certification grades.

Investigation on Architecture and Energy End-Use Characteristics of Korean Apartments for Whole-Building Energy Simulation Modeling

Investigation on Architecture and Energy End-Use Characteristics of Korean Apartments for Whole-Building Energy Simulation Modeling

Performance assessment of active insulation systems in residential buildings for energy savings and peak demand reduction

Active insulation systems (AISs) in buildings are envelopes that integrate thermal insulation, thermal energy storage, and controls. Although different designs for AISs have been proposed in the literature, a comprehensive analysis of feasible AISs is lacking. This paper discusses the energy performance, peak demand reduction potential, and performance characteristics of an AIS that uses a concrete wall as thermal mass sandwiched between two solid-state thermal switches (STSs). These STSs change their thermal conductivity using an on/off metal switch to create or break a thermal bridge across the STS. This paper first describes the experimental setup, used to determine the ratio of thermal resistance during R-high (low thermal conductivity) and R-low (high thermal conductivity) states of the STSs. This ratio was then used in whole-building energy simulations to evaluate the performance of AIS walls across different climate zones with/without a freeze timer of 60 min. The timer was added to reduce the number of switches of STSs from one state to another, and hence the energy needed for these switches. Analysis of the switching frequency and interval of STSs, thermal conductivity of walls, impact of wall orientation, and heat transfer through the wall from the use of AIS at different climate zones/locations were performed. The simulation results show that the AIS can achieve energy savings ranging from ∼ 980 to 2,290 kWh in a single-family home with a floor area of ∼ 220 m2 compared with an IECC 2018 baseline. The energy savings was higher in dry climate zones which represent 17% of residential buildings in the United States, compared to humid or marine climate.

Origins of whole-building energy simulations for high-performance commercial buildings: Contributions of NATEOUS, SHEP, TACS, CP-26, and RESPTK programs

Previous studies have traced the earliest origins of today’s whole-building energy simulation programs, such as EnergyPlus, eQUEST, DOE-2.1E, TRNSYS, TRACE, and HAP, to two public simulation programs in the early 1970’s, including: the Post Office program and the NBSLD program. However, in the 1960’s, there were earlier public simulation programs that had a significant influence on developments of the Post Office and NBSLD programs and are therefore related to many of the today’s whole-building energy simulation programs but were not discussed in previous studies, including: the NATEOUS program, the SHEP program, and the TACS program. In addition, there were public supplementary calculation programs that also contributed to developments of the Post Office and NBSLD programs, including: the CP-26 program and the RESPTK program. Therefore, the purpose of this study is to further clarify the earliest origins of today’s whole-building energy simulation programs based on the analysis of these early computer programs. This study extends the previous research (Oh and Haberl 2016) that discussed the origins of today’s whole-building energy simulation programs for high-performance commercial buildings and the thermal analysis methods used in these programs.

Experimental data for validation of a naturally ventilated single-story Double Skin Facade in whole-building energy simulation tools

Experimental data for validation of a naturally ventilated single-story Double Skin Facade in whole-building energy simulation tools

Models for validation of a naturally ventilated single-story Double Skin Facade in whole-building energy simulation tools

Models for validation of a naturally ventilated single-story Double Skin Facade in whole-building energy simulation tools

Modelling double skin façades (DSFs) in whole-building energy simulation tools: Validation and inter-software comparison of naturally ventilated single-story DSFs

Building energy simulation (BES) tools offer the possibility to integrate double skin façade (DSF) technologies into whole building simulation through dedicated modules or possible workarounds. However, the reliability of such tools in predicting the dynamic heat and mass transfer processes within the DSFs is still to be determined. Therefore, this paper aims to assess the performance of four popular BES tools (i.e. EnergyPlus, TRNSYS, IDA-ICE and IES-VE) in predicting the thermal behaviour of one-storey naturally ventilated DSF in three different ventilation modes. To evaluate their capability to predict thermophysical quantities, we compared the simulation results with experimental data. The results show that it is not possible to identify a tool that outperforms the others for all the analysed quantities, especially for the cavity air temperature, which is the least accurate parameter in all software due to underestimation of the daytime peak. IES-VE seems to be most accurate for Supply Air and Thermal Buffer modes when shading is deployed, while EnergyPlus appears most accurate for Outdoor Air Curtain mode. When it comes to surface temperatures and transmitted solar radiation, TRNSYS appears to be the best-performing software. In addition, this study investigated the challenges that designers may face when modelling a naturally ventilated DSF using whole-building simulation tools. Moreover, the investigation elucidates the challenges that have a more significant effect on the performance of the BES tools in order to reinforce their reliability.

Development, testing, and evaluation of the daylighting, thermal, and energy-saving performance of semitransparent radiative cooling glass in cooling-dominated regions

Glass-made building envelopes play an essential role in buildings’ thermal/daylighting environment and energy behavior. To enhance its overall energy efficiency in cooling-dominated regions, a double-layer film that combines the concepts of selective solar utilization (SSU) and radiative cooling (RC) is proposed to form the semitransparent energy-saving glass (SESG). The SSU film (∼0.1 mm) is a multilayer optical film that contains polyethylene terephthalate (PET) and thin reflective metal layer. The RC film (∼0.1 mm) consists of a PET layer and an adhesion layer. To evaluate the daylighting, thermal, and energy-saving performance of the SESG on buildings, comparative field tests using reduced-size model boxes and whole-building energy simulation analysis on a larger-scale office building are conducted. Compared with the normal clear glass, the developed SESG decreases the indoor air temperature of the modeled box by maximum values of 19.1℃ and 17.8℃ while reducing the daylighting level by 68 % to support a more comfortable thermal/daylighting environment. In addition, a single-story office building modeling using EnergyPlus was developed to evaluate the energy-saving and daylighting performance of the SESG in two different cooling-dominated cities, Male (Maldives) and Hong Kong (China) considering different glazing ratios. Compared with normal clear glass which will add amounts of extra cooling load and cause serious glare problems due to its high transmittance to visible light and near-infrared solar radiation, the annual cooling energy savings of the SESG reach 15 %—60 % in two selected cities under different glazing ratios. By considering both energy-saving potential and daylighting quality, the simulation results show that in Male, within the glazing ratios of 0.4 to 0.6, the UDI (Useful Daylighting Illuminance) values and energy-saving potential both reach the highest value of 0.5–0.6 and ∼ 55 %. In Hong Kong, the UDI values and energy-saving potential both reach the highest value of 0.4–0.5 and ∼ 57 % when the glazing ratio ranges between 0.5 and 0.9. The experimental and simulation results validate that combining selective solar utilization and radiative cooling for the glass envelopes is able to seek a more efficient balance between the energy behaviors and daylighting environment for buildings in cooling-dominated regions.

Modeling and demand-based control of responsive building envelope with integrated thermal mass and active thermal insulations

The static nature of current envelope design and operation is diametric to the mutable and transient forces and energies acting on our building stocks. Responsive building envelopes (or RBEs) have shown substantial energy saving potential for buildings by adaptively providing passive cooling/heating. In this research, an easy-to-implement yet flexible ‘demand-based’ control rule is proposed based on demand analysis to optimally control RBEs that integrate active insulation systems (AISs) and a sensible thermal energy storage (TES) layer. The controller developed herein calculates the desired thermal resistance for AIS layers and provides on-demand control of the heat flow into and out of the thermal mass to reduce AC load. It provides several benefits over the simple temperature-based controllers while does not require the complex formulation as needed for model predictive control. To quantify the thermal behavior and energy performance, a thermal network model is developed for RBEs to perform wholebuilding energy simulations of a residential thermal zone in six representative cities in the US. The results show apparent benefits of demand-based control strategy over traditional temperature-based control by offering higher energy savings and LPD reduction, especially in mild climate zones and during transitional seasons. Some design and implementation considerations for REBs with integrated AISs and TES are also discussed.

Overview of whole-building energy engines for investigating energy-related systems

Abstract With the rapid importance of high-performance energy modeling of buildings, whole-building energy simulation engines are rapidly used in the decision-making process. However, there are tens of engines in the market, which makes the choice of design engine very challenging. This article provides a comparison of the applications of whole-building energy simulation to predict a significant number of systems. As a result, the selected engines will be compared to establish their characteristics and abilities. Nevertheless, the focus will be placed on: generic criteria; envelope; lighting; service hot water; Heating-ventilation; and renewable systems. However, the authors found that an engine could be used extensively in one system and has limited capabilities in another system.

Urban heat mitigation through improved building energy efficiency

Buildings play a significant role in indoor and outdoor exposure to heat in urban areas. In this study, we quantify the heat mitigation potential of typical building energy efficiency measures that are often not considered as urban heat mitigation strategies, such as added insulation. We combined whole-building energy and urban climate simulations to compare indoor and outdoor (pedestrian-level) heat exposure with different levels of energy efficiency and under different climate timeframes in a soon-to-be-built public housing project in Phoenix, AZ. We found that improved energy efficiency reduces indoor and outdoor exposure to heat while climate change increases both. Considering the 2018 version of the energy code as the baseline, the mitigating impact of upgrading energy efficiency on indoor exposure to heat (as defined by% of year Tindoor > Tcooling setpoint +1 °C) exceeded the increase caused by climate change. Our estimates show a 6.6% increase caused by climate change vs. 20.7% reduction due to improved efficiency. Furthermore, our results indicate that energy upgrades may also have an impact on outdoor heat exposure (as defined by% of year with Toutdoor> 40 °C) due to reduced heat emitted from the buildings and their HVAC systems. We found a 2% increase in exposure caused by climate change vs. 1.4% reduction due to by improved efficiency. This suggest that upgrading energy efficiency of buildings may at least partially offset the impact of climate change on outdoor exposure to heat in the modelled urban canyon.

Assessment of the Impact of Using a Smart Thermostat and Smart Meter Data on a Whole-Building Energy Simulation

Building energy simulation models have been used to assist the design and/or optimization of buildings energy performance. The results from building energy simulation models can be more reliable when measured energy use data, indoor environmental condition data, system operation status, and coincident weather data are used to validate the simulation results. In this paper, given the wide-spread use of home automation devices in residential buildings, we studied how well a residential building energy simulation model can be tuned using measured interval data from a smart thermostat and smart meter. The analysis is based on a multi-stage approach that can help improve the reliability of the use of building energy simulation models that reflect both the indoor air temperature and whole-building energy use. Results from changing the input parameters in the building simulation show that the comparison of the simulated and measured indoor temperatures fall in a range below a NMBE of 1.5% and a CV-RMSE of 2.2%, while the simulated whole-building energy use matches the measured energy use below a NMBE of −2.7% and a CV-RMSE of 10.9%. We found that the most significant parameters for the indoor air temperature and whole-building energy use were the effective U-value for the slab-on-grade floor and the heating and cooling system operation status, respectively.

Energy savings potential of reversible photothermal windows with near infrared-selective plasmonic nanofilms

A variety of dynamic window and glazing systems with variable solar heat gain control features reacting to seasonal weather conditions and indoor space heating and cooling demands have been investigated in the past several decades. However, the modulation of solar heat gain has to affect the solar light transmittance in most existing dynamic glazing and window systems. In this work, a new type of dynamic window concept was proposed: reversible photothermal windows based on nanoscale solar infrared-induced plasmonic photothermal effects, which can modulate solar heat, independent of visible light conditions. This study provides the underlying technical characteristics and the thermal and optical features under solar irradiation via experimentally validated analytical models. The reversible photothermal windows exhibit a substantial ability to control solar heat gain coefficient with a range between about 0.2 and 0.6 and a stable visible transmittance of 0.32, A whole-building energy simulation demonstrates the potential for energy savings offered by reversible photothermal windows could reach over 18% in mixed climates, as compared to baseline models built using the most recent energy efficiency standards. This research illustrates technical and numerical evidence and mechanisms for energy savings that will support future research and development of this new dynamic window technology.

A procedure for automating thermal zoning for building energy simulation

Although many previous studies have addressed the accuracy of building energy simulations, very few studies of this subject have mentioned the importance of Heating, Ventilation, and Air-Conditioning (HVAC) thermal zoning strategies to sustainable building design. In addition, the building energy standards and guidelines related to building energy simulation recommend that only a core and perimeter thermal zoning strategy be used to reduce the total number of thermal zones in a model. However, although this simplifies modeling, it can lead to too many thermal zones in the building energy model of a multi-story building, or in some cases too few zones, which can impact the model's accuracy. Therefore, the aim of this study is to develop a new thermal zoning process for building energy simulation called the “grid/cluster method.” that can be applied automatically to whole-building energy simulations of multi-zone commercial structures. To verify this new thermal zoning method, the indoor temperature profiles of grid units were carefully analyzed in a case study simulation. In this study, three thermal zoning simulation models for a rectangular building were created and applied in heating- and cooling-dominant climates. The results show that for both climate conditions, the new grid/cluster method reduced heating/cooling loads by 11%–27% as compared to the single-zone model. In addition, the results significantly improved the simulated indoor comfort conditions.

Evaluation of phase change plaster/paste composites for building envelopes

Thermal energy storage (TES) materials increase a building’s thermal mass and provide the flexibility to shave and time-shift energy use. These materials are needed to enable grid-interactive efficient buildings, allowing building occupants to lower costs by leveraging free ambient heating/cooling as well as shifting consumption to cheaper electricity periods. Phase change materials (PCMs) that store heat through a solid–liquid/solid–solid transformation are of particular interest for TES because of their ability to store large amounts of energy across a constant temperature or very small temperature range. Previous studies on PCM building envelopes evaluated products that may only be incorporated as part of new construction and are not easily applicable to existing, energy-intensive buildings. In this work, we leverage laboratory PCM characterization and whole-building energy simulation to study the energy and cost savings of PCM plaster/paste coatings, which can be applied post construction to both new builds and retrofits of existing buildings (about 40% of residential buildings in the United States fall into the retrofit category). We evaluated the energy impact of PCM plaster/paste composites for a single-family residential building in the United States, including layer design (location and thickness), composite properties (phase change temperature, energy density, and shape of the enthalpy curve), and U.S. climate zone. The enthalpy curve shape of PCM shows that phase change temperature and energy density are not the only two parameters that must be considered for PCM selection. Maximizing the energy density amid the effective TES zone is key to boosting energy savings. We also studied PCM price targets with the aim of achieving reasonable payback periods based on both block and time-of-use electricity rates. Moreover, we developed an empirical equation to provide a rough estimate of the energy savings potential of incorporating PCM without the need to perform detailed simulations. These results will help guide the selection and design of PCM plaster/paste composite elements for residential building envelopes.

Modelling double skin façades (DSFs) in whole-building energy simulation tools: Validation and inter-software comparison of a mechanically ventilated single-story DSF

Double skin façades (DSFs) have been proposed as responsive building systems to improve the building envelope’s performance. Reliable simulation of DSF performance is a prerequisite to support the design and implementation of these systems in real buildings. Building energy simulation (BES) tools are commonly used by practitioners to predict the whole building energy performance, but the simulation of the thermophysical behaviour of DSFs may be challenging when carried out through BES tools. Using an exhaust-air façade case study, we analyse and assess the reliability of four popular BES tools when these are used to simulate a DSF, either through available in-built models or through custom-built representations based on zonal models. We carry out this study by comparing numerical simulations and experimental data for a series of significant thermophysical quantities, and we reflect on the performance and limitations of the different tools. The results show that no tool is outstandingly better performing over the others, but some tools offer better predictions when the focus is placed on certain thermophysical quantities, while others should be chosen if the focus is on different ones. After comparing the different models’ limitations and challenges, we conclude that BES tools can simulate the performance of DSF systems over long periods. However, their use alone is not recommended when the simulation’s scope is to replicate and study short-term phenomena and dynamic aspects, such as sizing the building’s HVAC system.

Recent Developments in the Design of Vertical Borehole Ground Heat Exchangers for Cost Reduction and Thermal Energy Storage

AbstractGround source (geothermal) heat pumps (GSHPs) can meet the thermal demands of buildings in an energy-efficient manner. The current high installation costs and long payback period limit the attractiveness of GSHP installation in the United States. Vertical borehole ground heat exchangers (VBGHEs), which are commonly used in GSHP systems, contribute most to the cost premium of GSHPs. Reducing the cost of VBGHEs could help increase market penetration of GSHP systems. This paper reviews recent developments for VBGHEs, including improvements in borehole heat transfer and borehole field layout, integration with thermal energy storage, and new design tools. Improvements in the borehole design and materials are more likely to be justified when the ground has high thermal conductivity. Integrating thermal energy storage can provide additional value to the GSHP system, especially when flexible electric demand at buildings becomes more valuable. Advanced design tools for VBGHEs that account for the thermal response of irregularly shaped borehole fields and that are more closely integrated with whole-building energy simulation programs may facilitate more innovations and optimization of GSHP system designs.