• Energy Research

Tools and experience on solar thermal cooling system sizing and design are still limited, as less than one thousand plants have been built until now. In this paper, a design tool for mid-size thermal solar cooling systems is presented. The tool consists of a model realised in TRNSYS and validated using the data of a real solar air conditioning system installed in the green building of Shanghai Research Institute of Building Science. Characteristic features of the system are the use of adsorption chillers driven by low-temperature solar heat from U-type and heat pipe evacuated solar collectors. The model has subsequently been employed for a technical analysis: the most relevant parameters have been varied and figures of merit calculated. An energy analysis has been performed for 6 reference cities, differing for climates and latitudes, highlighting the possibility to use only renewable energy for cooling purposes. Eventually, the systems have been compared with reference ones. Comparison highlighted that considerable savings in primary energy and CO2 emissions can be achieved: 0.97 MWh per installed square meter of solar collectors and up to 22 tons of CO2 annually, thus indicating a great potential for increasing energy efficiency and reduce CO2 emissions.

SAPO-34 - a silicoaluminophosphate microporous material - has recently attracted a great attention in the field of sorption thermal storage, since it is characterized by good water adsorption behavior (i.e. type V adsorption isotherms) and low regeneration temperature (i.e. 80 degrees C, for instance available by standard solar thermal energy collectors). However, the nanoscale mechanisms of water transport and adsorption in the microporous framework of SAPO.34 cannot be fully unveiled by experiments alone. In this work, water adsorption onto SAPO-34 is for the first time studied by means of an atomistic model built upon experimental evidence. First, Monte Carlo simulations are employed to set up a convenient atomistic model of water/SAPO-34 interactions, and numerical adsorption isotherms are validated against experimental measures. Second, the validated model is used to study the water diffusion through SAPO-34 by molecular dynamics simulations, and to visualize preferential adsorption sites with atomistic detail. Such atomistic model validated against experiments may ease the investigation and in silico discovery of silicoaluminophosphates for thermal storage applications with tailored adsorption characteristics.

In order to reduce the dependence on fossil fuels in the residential sector, low-carbon-footprint technologies such as heat pumps should be used. To fully exploit solar-assisted heat pumps, an effective control strategy is required. This study employs a low-global-warming-potential (GWP) refrigerant for a water-to-water reversible heat pump, which is assisted by a thermal energy storage tank, photovoltaic (PV) installation, and battery storage system using a dedicated control strategy. The heat pump’s operation is validated against the experimental data. Simulations are carried out for three different climates to analyze the performance of reversible heat pumps across Europe. The reversible heat pump fully meets the summer cooling demand in all three climates, while the heating demand is covered with the help of a backup source. An economic analysis is carried out for three different PV sizes and the results are compared with the reference energy systems. The inclusion of a battery storage system results in high payback times but increases overall flexibility and self-sufficiency.

Deep dehumidification is crucial for industrial applications requiring ultra-low humidity levels. Traditional cooling-based dehumidification struggles to achieve low dew points efficiently due to excessive energy consumption and frost formation risks. As an alternative, desiccant-based methods, particularly solid desiccant systems, offer improved performance with lower energy demands. This study experimentally investigates a fixed-bed dehumidification system utilizing a plate-fin heat exchanger filled with a silica gel/calcium chloride composite material. The performance evaluation focuses on the influence of ambient conditions and operating parameters, including air velocity and cooling fluid temperature. Among these, the most influential parameter was the velocity of air. For the tested heat exchanger, an optimum value in the range of 0.4–0.6 m/s was identified. Under optimal conditions, the tested HEX was able to reduce the dew point of air down to −2 °C, achieving a reduction in the humidity ratio up to 13 g/kg. The results indicate that air velocity significantly impacts also heat and mass transfer, with coefficients ranging from 80 to 140 W/(m2 K) and 0.015 to 0.060 kg/(m2 s), respectively. The findings highlight the potential of composite desiccant fixed-bed systems for efficient deep dehumidification, outperforming conventional lab-scale components in heat and mass transfer effectiveness. A comparison with other works in the literature indicated that up to 30% increased mass transfer coefficient was achieved and up to seven times higher heat transfer coefficient was measured.

The present paper reports the design, realization and testing of a lab-scale latent heat storage, specifically realized for solar cooling applications. The latent heat storage is based on a fin-and-tubes heat exchanger configuration employing a commercial paraffin as PCM. The paper mainly focuses on the experimental characterization, carried out by means of a test rig, available at the laboratory of the CNR ITAE, able to simulate working boundaries of a solar cooling plant. The experimental outcomes confirmed the increased heat storage density obtained by such a new component, compared to standard sensible heat storage. Nevertheless, still some limitations in the achievable heat transfer rate is highlighted, due to improper realization of the component.

The efficient utilization of renewable energy sources should rely on the exploitation of a mix of thermal and electric energy rather than relying on a single energy source. One way to apply this shared generation concept to space heating/cooling and refrigeration in both residential and industrial sector is through hybrid sorption-compression chillers. However, the experience on these systems is still limited and therefore their design and optimization require some efforts. Starting from the experimental experience on the testing of different hybrid cascade chillers, and integrating the measurement with a dynamic model, some considerations on the sizing, design and optimization of hybrid thermal-electric chillers are reported. In particular, design conditions of pre-commercial or commercial systems are evaluated and optimization at different levels is proposed, i.e. on the core components (through the proper design of relative capacities of the units in the cascade and through proper selection of the refrigerant), on the auxiliaries, to reduce their electricity consumption, and on the overall management of the hybrid chiller. Results demonstrated that the higher is the operating temperature lift between evaporator and condenser the higher are the achievable energy savings of a cascade chiller. (C) 2020 Elsevier Ltd. All rights reserved.

This project report presents the main features of the three Key Enabling Technologies that are being developed within HYPERGRYD. The technologies under investigation are Modular Heat Pump with short-term PCM storage, a Sorption Thermal Energy Storage, and a Reversible micro-CHP with steam engine and steam buffer. The report delves into the main specifications and technical drawings of each technology, demonstrating the current advancement level of the development within HYPERGRYD project. The Modular Heat Pump with short-term PCM Storage technology offers a scalable and efficient solution for heating and cooling applications. It employs phase change materials (PCM) to store thermal energy for DHW, releasing it during peak demand, thus optimizing energy consumption. The Sorption Thermal Energy Storage introduces a novel approach to energy storage through reversible physical-chemical reactions. This closed-loop system utilizes composite materials to store and release energy in the form of heat, demonstrating excellent energy density and prolonged storage durations for both heating and cooling. The Reversible micro-CHP with steam engine and steam buffer combines heat and power generation, achieving enhanced system efficiency through waste heat recovery. By utilizing a reciprocating piston engine, it simultaneously produces electricity and captures waste. This recovered heat finds applications in heating, or industrial processes, making the cogeneration unit a versatile and fuelflexible choice. The report is a document intended for HYPERGRYD consortium members, in particular to the pilot owners where the Enabling Technologies will be installed and the owners of tools from HYPERGRYD platform, who can use the provided drawings and specifications as inputs for the tools/platform.

Hybrid sorption-compression systems are gaining interest for heating/cooling/ refrigeration purposes in different applications, since they allow exploiting the benefits of both technologies and a better utilization of renewable sources. However, design of such components is still difficult, due to the intrinsic complexity of the systems and the lack of reliable models. In particular, the combination of adsorption-compression cascade unit has not been widely explored yet and there are no simulations or sizing tools reported in the literature. In this context, the present paper describes a model of a hybrid adsorption-compression system, realised in Modelica language using the commercial software Dymola. The models of the main components of the sorption and vapour compression unit are described in details and their validation presented. In addition, the integrated model is used for proving the feasibility of the system under dynamic realistic conditions and an example of the technical sizing that the model is able to accomplish is given.