Conference Agenda

Cabin heating of electric vehicles can have a significant negative impact on vehicle range. Thus, the objective of this work is to analyze the potential implementation of a thermochemical energy storage module (TCESm) integrated with a heat pump for augmenting cabin heating of electric vehicles in cold climates and reducing the need for battery storage. First, the thermal properties of the most promising salt hydrate-based thermochemical materials were investigated on the basis of mass, volume, cost, and temperature lift capability. From this, the reversible strontium bromide monohydrate to strontium bromide hexahydrate hydration reaction was identified as the most promising for use in an open TCESm, where moisture in the ambient air exothermically hydrates the salt. Then, a baseline EV thermodynamic heat pump design was specified and integrated with a model for the TCESm. The TCESm model used a lumped approach that considered the reaction kinetics as a function of time and the extent of reaction. Two TCESm heat pump integrated configurations were considered. In the first, a TCESm was supplied moisture and heated incoming evaporator air, to increase the EV heat pump evaporator saturation temperature. In the second, heated cabin air leaving the condenser was further heated in a TCESm, allowing the heat pump to run at a reduced capacity. At a baseline ambient condition of -10°C and 30% relative humidity, the first system showed a negligible improvement of heat pump COP of 1.9%. For the second case, the compressor work could be reduced between 40 and 50% at an ambient dry-bulb of -10°C and for between 5 and 10 kg of salt.

In multi-family buildings, large water storage tanks in centralized domestic hot water (DHW) systems can serve as thermal energy storage (TES) batteries to mitigate grid impact. These systems offer demand shift and efficiency benefits, significantly reducing peak power consumption, particularly in cold climates.

This study evaluates the performance of a centralized DHW system equipped with a CO2 heat pump water heater in multi-family buildings through simulation. The heat pump system and water storage tank are sized using design-day sizing. A generic stratified tank model is developed and validated against performance data from a commercial DHW product. To assess the potential of the centralized DHW system for energy efficiency improvements, load-shifting, and emission reductions, annual simulations are conducted using EnergyPlus. These simulations incorporate utility tariffs and marginal grid emission data from selected territories.

Results from this study demonstrate that the TES-enabled DHW system offers significant benefits on load shifting and emission reduction. In Chicago, compared to conventional electric resistance water heaters, TES-enabled DHW system provides a 22% utility cost saving and a 32% emission reduction. Compared to conventional heat pump water heaters without TES capability, TES-enabled DHW system achieves a 14% utility cost saving and a 29% emission reduction.

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Clothes drying is an energy-intensive process that causes significant electricity consumption and carbon emissions in the US. Approximately 83% of Households in the US own a tumble clothes dryer at home and 80% of dryers are electrical resistance dryers with low energy efficiency. The use of heat pump technology makes it possible for highly efficient and clean drying. Additionally, the ventless design of heat pump clothes dryers (HPCD) provides more installation flexibility. HPCD involves three primary mediums - wet clothes, a closed air loop, and a refrigerant circuit. The evaporator is used to dehumidify the wet air and the condenser is used to re-heat the dry air. One of the critical technological barriers to HPCD market penetration is its long drying time, primarily due to the relatively low discharging temperature and the slow response during the warm-up period. In this study, the thermal energy storage (TES) technology is adopted to address this challenge by providing pre-heating of air prior to the condenser to increase the operating temperature of the process air. The heat pump will charge the phase change material (PCM) in the TES device with heating energy during clothes washing and the PCM will discharge the stored heat to facilitate air heating during clothes drying. To analyze the optimal design and potential for energy saving and drying time reduction, a mathematical model of the HPCD system was developed. The HPCD is a highly dynamic system with a coupled heat and mass transfer and heat pumping cycle. This paper provides solutions to simulate the transient behavior of the system while maintaining low computational cost. Different drying system designs are simulated, and parametric studies are conducted. The modeling result indicates reduced energy consumption and drying time by integrating TES with HPCD, as compared to electrical resistance dryers. The study can provide significant insights into improving building flexibility with TES and smart appliances.

The intermittent nature of renewable electrical energy generation poses significant challenges to maintaining electrical grid stability. Grid-scale electrical storage is not currently feasible, but a potential solution is the use of load-side Thermal Energy Storage (TES). Demand-side management, with TES as a promising component, is essential for future modern grids with a high share of intermittent, non-dispatchable, renewable electricity. Given the increasing momentum in research on TES solutions, efficient numerical models are needed for accurately modeling TES systems. As a relatively new component in buildings’ HVAC systems, further studies are needed to investigate feasibility of these thermal batteries.

The ground has lower temperature variation compared to the ambient air, resulting in lower heat losses from a TES tank in the heating season and lower heat gains to the tank in the cooling season. In this study, we focused on modeling a stratified thermal energy storage tank that is buried in the ground. We developed a two dimensional (2D) numerical model in cylindrical coordinates capable of simulating the thermal interaction between the stratified tank and the ground over extended periods. The overall research goal of the project is optimization of the tank design parameters such as geometry, burial depth, and insulation thickness combined with a techno-economic analysis that provides design guidelines for a buried TES.

The intermittent nature of renewable electrical energy generation poses significant challenges to maintaining electrical grid stability. Grid-scale electrical storage is not currently feasible, but a potential solution is the use of load-side Thermal Energy Storage (TES). Demand-side management, with TES as a promising component, is essential for future modern grids with a high share of intermittent, non-dispatchable, renewable electricity. Given the increasing momentum in research on TES solutions, efficient numerical models are needed for accurately modeling TES systems. As a relatively new component in buildings’ HVAC systems, further studies are needed to investigate feasibility of these thermal batteries.

In this study, we focused on numerically modeling a one dimensional (1D) stratified thermal energy storage tank filled with water. Three numerical discretization schemes, namely Second Order Upwind (SOU), Crank Nicolson (CN), and Hybrid are employed to develop three numerical models. Simultaneously, we developed a TES tank experimental facility fully automated to replicate real-world scenarios of charging, storage, and discharging. Additionally, instances where adverse feed temperatures occur, resulting in increased mixing in the tank, are also investigated. The experimental results are used to validate the comprehensive tank models, so that they can accurately predict the tank's behavior across all usage scenarios. Finally, we discuss and compare the advantages and disadvantages of each model, providing the reader with insights for model selection.