A nationwide assessment of energy flexibility from predictive-controlled heat pump and active thermal energy storage system for building electrification

Evaluation of Energy Savings by Optimization Control in Thermal Energy Storage System

A demand response method for an active thermal energy storage air-conditioning system using improved transactive control: On-site experiments

Smart grid coordination in building HVAC systems: EMPC and the impact of forecasting

The substantial peak electrical demand for space heating in cold and freezing climates poses a significant challenge to grid stability and energy affordability. This study proposes and numerically investigates a novel active thermal energy storage system integrated directly into a building brick to address this challenge. The system features an encapsulated Phase Change Material (PCM) composite, enhanced with a high-conductivity copper oxide foam, and is coupled with a low-wattage electrical heating element. This design enables the brick to function as a 'thermal battery,' charging with off-peak electricity and discharging heat during peak demand periods. A comprehensive computational fluid dynamics (CFD) model was developed to analyze the system's performance under severe winter conditions, with ambient temperatures as low as -30°C and varying electrical power inputs. The results demonstrate a profound improvement in the indoor thermal environment. While an unheated brick's surface dropped to -5°C, the active system maintained it above a stable + 8°C, delivering a peak heat output of over 150W/m² to the living space. This effective load shifting reduced the wall's net daily energy loss by nearly 70%, significantly lessening the burden on the primary HVAC system during peak hours. The findings confirm that the proposed active PCM-brick is a highly effective and viable solution for peak-shaving, enhancing occupant comfort, and improving the energy resilience of buildings in cold climates.

sandTES – An Active Thermal Energy Storage System based on the Fluidization of Powders

An encoder–decoder LSTM-based EMPC framework applied to a building HVAC system

Those that use electricity for water heating, the majority use resistive elements rather than heat pump water heaters (HPWHs), the latter of which use 60-70% less energy than the former. One major barrier to wider HPWH adoption is the added equipment required, which prevents current 50-80-gallon tanks on the market from fitting into smaller utility closets sized for 30-40 gallons, such as those found in manufactured housing. Additionally, these smaller HPWHs tend to underperform relative to their larger counterparts. One solution that addresses both space and performance concerns is thermal energy storage, and in particular, phase change materials (PCMs). PCMs have been studied extensively in building envelope and HVAC systems, but remain a nascent technology in residential water heating. While water itself has a uniquely high energy storage capacity, PCMs have an even higher energy storage density, thus providing the potential to elevate the performance of 40-gallon HPWHs to that of 50-gallon or larger tanks. This research is part of a larger project that seeks to utilize thermal energy storage to enable decarbonized water heating in low-income communities. In this study, we outline the design process used to produce novel PCM heat exchangers for use in small-volume HPWH tanks, including the identification of design constraints and performance targets relevant to real-world applications. In order to ensure optimal PCM utilization and tank storage capacity, we focus here on co-maximizing surface area and PCM volume in the heat exchangers; therefore, this research targets triply periodic minimal surface (TPMS) lattices. TPMS lattices boast enhanced heat transfer capabilities compared to traditional heat exchanger geometries and offer highly tailorable designs; thus, they pair well with the growing field of additive manufacturing, or 3D printing. Starting with a suite of TPMS lattices, we demonstrate a systematic approach for narrowing down feasible designs that comply with identified constraints while meeting PCM performance objectives.

Heating, ventilation, and air-conditioning (HVAC) systems account for the largest share of energy consumption in European Union (EU) buildings, representing approximately 40% of the final energy use and contributing significantly to carbon emissions. Latent thermal energy storage (LTES) using phase change materials (PCMs) has emerged as a promising strategy to enhance HVAC efficiency. This review systematically examines the role of latent thermal energy storage using phase change materials (PCMs) in optimizing HVAC performance to align with EU climate targets, including the Energy Performance of Buildings Directive (EPBD) and the Energy Efficiency Directive (EED). By analyzing advancements in PCM-enhanced HVAC systems across residential and commercial sectors, this study identifies critical pathways for reducing energy demand, enhancing grid flexibility, and accelerating the transition to nearly zero-energy buildings (NZEBs). The review categorizes PCM technologies into organic, inorganic, and eutectic systems, evaluating their integration into thermal storage tanks, airside free cooling units, heat pumps, and building envelopes. Empirical data from case studies demonstrate consistent energy savings of 10–30% and peak load reductions of 20–50%, with Mediterranean climates achieving superior cooling load management through paraffin-based PCMs (melting range: 18–28 °C) compared to continental regions. Policy-driven initiatives, such as Germany’s renewable integration mandates for public buildings, are shown to amplify PCM adoption rates by 40% compared to regions lacking regulatory incentives. Despite these benefits, barriers persist, including fragmented EU standards, life cycle cost uncertainties, and insufficient training. This work bridges critical gaps between PCM research and EU policy implementation, offering a roadmap for scalable deployment. By contextualizing technical improvement within regulatory and economic landscapes, the review provides strategic recommendations to achieve the EU’s 2030 emissions reduction targets and 2050 climate neutrality goals.

This paper studies the potential of shifting the heating energy consumption in a residential building to low price periods based on varying electricity price signals suing Economic Model Predictive Control strategy. The investigated heating system consists of a heat pump incorporated with a hot water tank as active thermal energy storage, where two optimization problems are integrated together to optimize both the heat pump electricity consumption and the building heating consumption. A sensitivity analysis for the system flexibility is examined. The results revealed that the proposed controller can successfully achieve significant shifting potentials compared to a baseline case.

A large potential to shift the electricity consumption to adapt to the stochastic renewable electricity generation is identified through the utilisation of a combination of Heat Pumps (HP) and local Thermal Energy Storage (TES) devices in building heating systems. In this paper, a building heating system coupled with an active Phase Change Material (PCM) TES device and a HP is simulated to characterise its potential for Demand Response (DR) applications. A control-oriented numerical model for the PCM TES is developed and previously validated numerical models of the building, HP and hot water radiators are integrated to simulate the dynamics of the coupled building heating system. A Genetic Algorithm (GA) based control strategy is designed to optimise the building heating energy consumption and operational cost with respect to time-varying electricity price signals. The developed control strategy is successfully implemented to utilise the TES capability of the PCM and the thermal inertia of the building to intelligently shift the electrical load of the HP to low price periods, while satisfying the specified indoor comfort requirements. In comparison to a reference case utilising a sensible TES, cost savings and consumption reductions of more than 40% and 30%, respectively, are attained with the active PCM TES. Simulation results indicate that utilising an active PCM TES over a sensible TES offers significant advantages for DR applications in building heating systems in terms of load shift flexibility, energy costs and consumption.

To mitigate the variation in demand on the electric grid, thermal energy storage (TES) is an alternative to electric batteries or installing new peaking power plants. Stakeholders and policy makers across the United States have expressed interests in promoting TES, as demonstrated by the US Department of Energy’s Grid-Interactive Efficient Buildings program and the efforts of various state legislatures. However, the cost value provided by TES are unclear. If reliable cost benefits were determined, stakeholders would have a clearer picture of the financial returns that can be gained from their investment in TES. The study in this report is conducted by ORNL with collaboration with Emerson the Helix Innovation Center. In the first part of this report, EnergyPlus was used to perform whole-building simulations for two residential buildings in Indianapolis and Atlanta. The HVAC system in both buildings were equipped with phase change material TES. The TES tank was charged in off-peak hours and discharged in peak hours to perform load shifting. First, the economic value implied by existing time-of-use (TOU) rates offered by utility companies was analyzed via whole-building simulation. Second, existing demand reduction (DR) incentives sourced from 3 different electrical grid administrators (i.e., California, Texas, and New England region) were surveyed to determine their implied value. The study suggests that the traditional value analysis that focuses on ROI for the building owner significantly undervalues TES technology making economic viability difficult. A more comprehensive value analysis that includes peak demand management and deferred capital for peaking power plants shows that TES should be economically viable but here the value is greater for the utility and requires large market penetration and aggregation to fully realize the benefits. Therefore, to facilitate commercialization, new business models are needed that include a broader range of stakeholders and distribute the value of TES proportionally. In the 2nd part of this project, the benefits of a novel phase change material (PCM) integrated heat pump configuration were evaluated via detailed component based simulation. A one-dimensional PCM heat exchanger model which discretizes the PCM tank and refrigerant tubes into small control volumes is developed. Each control volume can have different PCM temperatures, PCM properties, and heat transfer coefficients. The PCM tank is charged by a wrapped tank condenser and discharged by an internal refrigerant coil. The PCM heat exchanger model is integrated into DOE/ORNL Heat Pump Design Model for heat pump system simulation. To demonstrate the performance of the PCM integrated heat pump, a case study in Chicago was performed. A Time-of-Use utility structure-based control strategy is implemented to schedule the PCM tank charging and discharging mode switching. Compared with a conventional electric heat pump, the PCM integrated heat pump shows superior performance on load shifting and utility cost reduction. As a result, the proposed system demonstrates 24.6% utility saving for cooling application and 25.8% utility saving for heating application.

Corrosion of metal and metal alloy containers in contact with phase change materials (PCM) for potential heating and cooling applications

Development and characterization of novel and stable silicon nanoparticles-embedded PCM-in-water emulsions for thermal energy storage

Heating ventilation and air conditioning (HVAC) systems usually account for the highest percentage of overall energy usage in large-sized smart building infrastructures. The performance of HVAC control systems for large buildings strongly depend on the outside environment, building architecture, and (thermal) zone usage pattern of the building. In large buildings, HVAC system with multiple air handling units (AHUs) is required to fulfill the cooling/heating requirements. In the present work, we propose an energy-aware building resource allocation and economic model predictive control (eMPC) framework for multi-AHU-based HVAC system. The energy consumption of a multi-AHU-based HVAC system significantly depends on how long the AHUs are running, which again is governed by the zone usage demands. Our approach comprises a two-step hierarchical technique where we first minimize the running time of AHUs by suitably allocating building resources (thermal zones) to usage demands for zones. Next, we formulate a finite receding horizon control problem for trading off energy consumption against thermal comfort during HVAC operations. Given a high-level building specification and usage demand, our computer-aided design framework generates building thermal models, allocates usage demands, formulates the control scheme, and simulates it to generate power consumption statistics for the given building with usage demands. We believe that the proposed framework will help in early analysis during the design phase of energy-aware building architecture and HVAC control. The framework can also be useful from a building operator point of view for energy-aware HVAC control as well as for satisfying smart grid demand-response events by HVAC system peak power reduction through automated control actions.

A characteristic-oriented strategy for ranking and near-optimal selection of phase change materials for thermal energy storage in building applications