Conference Agenda

A circumstance with both heating and cooling demands has emerged ubiquitously across building and urban scales. This scenario is ideally addressed by implementing the evaporator and condenser of a heat pump. However, an ongoing challenge exists to harmonize the time and amount of heat and cold production with the user’s demand. More importantly, determining the effectiveness of a heat pump’s dual functionality across diverse applications remains up in the air. In this paper, the integration of a heat pump and latent heat and cold storage is proposed. Two independent latent heat and cold storage units are integrated to align the time and amount between heat and cold generation and demand, thereby facilitating a demand-oriented thermal energy supply service. Simulations are performed in intermittent, alternate, and scattered heating and cooling scenarios. Based on second-law efficiency and exergy analysis, we establish thermodynamic criteria - ratio of power consumption (RP) and ratio of time spent (RT) - for systems with simultaneous heating and cooling mechanisms. Such simultaneous production can yield substantial energy savings of up to 46%, and double the output thermal power in some cases compared to alternate heating and cooling heat pumps. Nevertheless, the simultaneous heating and cooling mechanism proves challenging for a single-stage heat pump with significant temperature differences in achieving an appreciable competitive edge in RP and RT. Further refinement in heat pump design and refrigerant selection poses a research frontier.

The research conducted on phase change materials (PCMs) for latent thermal energy storages (LTESs) is continuously growing in terms of publications, pointing out the importance of this topic. In fact, PCMs present many advantages that could help the energy transition and reduce CO₂ emissions, by enhancing the performance of existing systems and better exploiting renewable energy. Therefore, it is of crucial interest to develop new and reliable methods to control LTES. Differently from sensible thermal energy storages, in LTESs the stored thermal energy is not proportional to the temperature. To really have an insight into the level of charge of these storages, it is important to know the liquid fraction, i.e., the amount of the liquid phase with respect to the whole amount of PCM. X-ray computed tomography (XCT) is a technology that allows to non-intrusively “look inside” the materials and, in the current study, it was used to analyse calcium chloride hexahydrate crystallization phenomenon. This transient process of calcium chloride hexahydrate was tracked with many XCT scans, one every 6 minutes, resulting in 3D image stacks that were processed to obtain the volumetric liquid fraction evolution over time. Repeatability tests were run to evaluate the reliability of the XCT technique and the volumetric liquid fraction data was used to validate a numerical model developed within ANSYS Fluent framework. XCT offers great opportunities to study the heat and mass transfer mechanisms underlying the main issues of phase change materials, like, for example, supercooling and salt hydrate segregation.

Refrigeration systems are an essential appliance for both commercial and residential applications. Thermal (Cold) energy storage can effectively reduce the carbon emission contributions from refrigerators. This study investigated the demand flexibility of a domestic refrigerator using thermal (cold) energy storage through dynamic modeling. The models include both the fresh and frozen compartments, vapor compression cycle loop, and thermal storage panels. Experimental data were collected to validate the models. Results show integrating energy storage into refrigerator can reduce the energy consumption by 30%, power demand by 20%, and carbon emission by 20%.

Integrating thermal energy storage (TES) with residential heating systems is an enabling technology for incorporating renewable sources into the electricity grid. In this paper, a system level model of a thermochemical energy storage system integrated with a residential heat pump is developed. A transient lumped model of the adsorption cycle is developed to investigate the dynamic charging and discharging characteristics of strontium bromide as an adsorbent material. The results obtained from this model are coupled with a vapor compression cycle model to analyze the performance of the integrated system. The heating coefficient of performance (COP) as well as discharging temperature and heat duty are analyzed for a range of cycle parameters, including charging temperature for the thermal storage and discharging temperature. The effect of storage duration on performance is also reported. A representative system operates with a COP of 2.6 and is capable of discharging at a temperature greater than 30°C for four hours, providing an average heat duty of 2.4 kW.

The Grid Independent High Efficiency System (GIHES) delivers a heating system that operates free from the power grid and provides ultra-low emissions and high efficiency heating for residential and commercial buildings. The project demonstrated two weeks of continuous grid independent operation of a storage water heater equipped with a powered damper. The Thermoelectric Generator (TEG) integrated GIHES technology revolutionizes heating systems to provide grid resilient hot water production, while delivering significant value to the end user by eliminating impacts of power interruption and enhancing comfort, convenience and productivity. The system maximizes the thermal-to-electric conversion efficiency by optimizing location and orientation of the TEGs and durability while lowering system costs. The TEGs generate enough power to charge a battery and run the storage water heater unit with a powered damper uninterrupted by providing the required parasitic electrical power for start-up, shutdown and during idling. Several TEGs were analytically and experimentally evaluated based on the size, surface area and the power being generated before designing and fabricating a complete multi-TEG assembly for integration with the water heater. The GIHES technology can be extended to boilers, furnaces and tankless water heaters and integrated with heat pump to further increase the overall equipment efficiency. The technology has the potential to reduce the amount of dispatch power and peak power plant operation.

Techno-economic analysis (TEA) of the TEG integrated with the water heaters was performed. The testing data and the power output were used to develop the TEA. The analysis for the storage unit with damper showed that the TEG integrated system costs are economical and are lower than the labor costs to install a dedicated power system. Discussions with TEG manufacturers and Original Equipment Manufaturers (OEM’s) will provide more detailed information and methods to further lower these costs.