Hycool - Deliverable 3.1:Optimization of the hybrid heat pump configuration and control strategy through dynamic modelling under different scenarios

This document is the deliverable "D3.1 - Optimization of the hybrid heat pump configuration and control strategy through dynamic modelling under different scenarios" of the European project "HYCOOL - Industrial Cooling through Hybrid system based on Solar Heat." (hereinafter also referred to as "HYCOOL", project reference: 792073). The present deliverable aims at defining a dynamic simulation tool for the modelling of the hybrid cascade chiller, which represents one of the core systems of the HYCOOL project. This system is based on the coupling of a thermally driven adsorption chiller and a vapour compression chiller. In particular, the operation of the adsorption chiller is primarily meant to dissipate the heat of condensation that needs to be rejected by the vapour compression chiller. In this way, reducing the temperature lift between evaporator and condenser, less compression work is needed and the energy efficiency ratio is improved. Firstly, a components selection was performed, in order to identify the most suitable refrigerant as well as the sizing of the heat exchangers, compressor and valves of the two machines. Particularly the refrigerant for the vapour compression chiller was selected by means of a thermodynamic optimization, coupled to considerations regarding the compressor sizing and its environmental impact. An innovative natural refrigerant, R290 (i.e. propane) was identified as the most promising for this application, also according to the current technology being developed by FAHRENHEIT. The dynamic model was implemented in the language Modelica through the software Dymola. It allowed exploiting standard libraries for the modelling of relevant components as well as physical phenomena, such as heat and mass transfer, which can be easily adapted to properly model the defined technology under investigation. For this reason, for all the components of the hybrid chiller, technical data from manufacturer datasheets and existing experimental data were used to make the model reliable. The implemented model was successfully validated against experimental data collected on a lab-scale prototype previously produced by FAHRENHEIT and tested at the CNR ITAE lab. The operation of a 20 kW cooling power machine, which will represent the rated power for the lab-scale experimental activity during the T3.3, was then simulated under different conditions. They represent the operation under variable heat source and sink and implement an experimental dynamic load profile provided by GIVAUDAN, whose meaningfulness can be extended also for the application to the Bo de Debò pilot plantThese simulations were used to optimize the ratio between cooling powers of the adsorption chiller and vapour compression chiller, demonstrating that the adsorption chiller needs to provide at least 20% more cooling power than the vapour compression one, to properly operate the hybrid configuration. Furthermore, some Key Performance Indicators were defined, namely, the cooling capacity and the thermal COP of the adsorption chiller and the average inlet temperature at the condenser of the vapour compression chiller. These were employed to comparatively evaluate the operation of the cascade chiller under different boundary conditions, thus highlighting which might be the most effective control strategy to maximize the overall efficiency. The outcome of this analysis was the identification of performance maps, as function of boundary conditions and part load, useful to identify the best management strategy of the cascade chiller and to give a comprehensive indication on its operation in different conditions The implemented simulation tool will be further refined as soon as all the components will be designed during the T3.2 and then used, during the T3.3 to identify further management strategies to be tested on the lab-scale prototype. The performance map obtained, which summarises the energy flows in and out from the hybrid heat pump will be employed during WP5 and WP6 as input for the control development and system integration design. Finally, it will represent a useful tool throughout the project also to support the sizing of the hybrid chiller for the demo site installations.