Conference Agenda

A dynamic model of automatic commercial ice maker was established on GT-SUITE platform to study the performance of a R404A commercial ice maker and verified with test results. The model was adapted to a R134a modification of this ice maker and compared its performance with test data too. Finite state machine tool provided by the GT-SUITE platform is employed to simulate the operation mode switching of automatic commercial ice maker.

This paper puts forward a computer methodology for designing low-pressure axial fan blades for small-capacity refrigeration applications. Based on the blade element theory (BET), the aerodynamic efficiency of the airfoil, the principles of mass and momentum conservation together with empirical correlations for the flow irreversibilities, a mathematical model was devised for screening the blade geometric parameters (e.g., radial chord and pitch variation, and hub radius) by varying the fan inductance distribution for a given blade diameter, motor speed, and airflow system characteristic curve. The best blade configuration is selected by means of a tailor-made optimization algorithm and undergoes a series of linear transformations for translating the fan parametrization into a CAD drawing. Two new fan blades were designed, one for maximum blade efficiency (MBE) and another for maximum airflow rate (MAR). In comparison with the free-swirl design approach, a standard procedure adopted in the open literature, the proposed blades showed an efficiency and an airflow by 20% (MBE) and 14% (MAR) higher than the reference. The airflow characteristics of the new designs were also assessed by means of wind-tunnel testing, which confirmed an increase of 11% in the case of MBE design, while an enhancement of 10% was observed in the case of MAR design.

The increased demand for energy efficient systems requires design workflows and engineering tools that can promote innovation, reduce costs, and accelerate product development. In the case of vapor compression cycles, such as heat pumps, model-based design has been successfully used to support different stages of the design process. For example, design exploration using steady state simulations or performance evaluation using dynamic analysis are continuously implemented with notable success. However, these studies and their conclusions seem to fall isolated and there is still a lack of synergy between both analyses. This could be attributed to many factors, and one could be the lack of tools that can support both technologies. This limitation may hinder the development of workflows that promote the interaction between both steady state and dynamic simulations.

This paper aims to present a convenient way to enhance the development process of vapor compression cycles, heat pumps specifically, by using the capabilities of Modelon Impact and Modelica to support both transient and dynamic simulations. These capabilities are applied to develop a workflow for the design of heat pumps seamlessly integrating both types of simulations into the design process. One part of the workflow focuses on the steady analysis for design exploration, sizing, and charge optimization. Thereafter, a selected set of optimized systems is evaluated using dynamic simulations for long term performance analysis, evaluating the response to variable ambient conditions, and implementing different control strategies. An advantage of this integrated approach for steady-state and control design is the complete consistency of the models, which is hard to achieve if the models are developed in separate platforms, as typically is the case. The open standards of Modelica and the Functional Mockup Interface (FMI) enable the integration of these models into cross-tool engineering workflows.

The results of our study demonstrate a significant enhancement in selected Key Performance Indicators (KPIs), specifically Coefficient of Performance (COP), Energy Consumption, and Seasonal COP. This improvement is pronounced when accounting for both the inherent design restrictions and the variability in performance conditions. Our analysis takes into consideration the complex interplay between these factors, providing a comprehensive understanding of how the system performs under realistic and diverse operating scenarios. The findings underscore the importance of integrating design considerations and accounting for real-world variability in evaluating and optimizing the performance of heat pumps.

Manufacturers and building energy modelers often depend on data-driven models that need a large amount of experimental data to produce heat pump performance maps. This work provides a new gray box model that reduces the need for extensive training datasets in comparison to empirical models. The proposed model combines fundamental physics-based principles with an empirical method to reliably forecast heat pump performance under various operating scenarios. Separate component models are formulated for the compressor and heat exchangers. The overall heat transfer coefficient is modeled through an empirical correlation utilizing only ambient temperatures and operational inputs to the heat pump. By incorporating additional physical characteristics to couple the component models using a system model, the model provides reliable predictions for cooling capacity, coefficient of performance, and sensible heat ratio. These predictions consistently exhibit a mean absolute percentage error of lower than 4% when tested over experimental data using smaller data sets that encompass the AHRI 210/240 mandated tests from 3.5- and 4-ton units.

The importance of energy conservation has greatly increased to promote the decarbonization in buildings. This has resulted in significant interest in variable-speed heat pumping systems with improved efficiency. This paper formulates and evaluates a variable heat pump system model compatible with Building Energy Modeling software like EnergyPlus. The model uses as inputs the indoor and outdoor temperatures along with indoor supply air and compressor speed of the heat pump system to predict the heating capacity and coefficient of performance (COP) with 11 data points for training purposes. The model predictions are compared against experimental data from two, state-of-the-art, variable-speed heat pump systems. The model can predict the capacity and COP of the variable heat pump system with 3% and 4% respectively.

The electrification of the thermal sector through refrigeration/heat pumps for space cooling and heating is a fundamental part of the energy transition. In this paper, dynamic models of different types of refrigeration/heat pump systems (air-air, water-water, air-water, water-air refrigeration/heat pumps) are developed and applied to estimate and compare their operation thermal characteristics. The main purpose of the paper is to show the benefits of water/water refrigeration/heat pumps and to emphasize their growing importance in the context of the 5^th generation district heating and cooling systems (centralized/decentralized refrigeration/heat pumps). The dynamic models are developed in Matlab and the thermodynamic properties of refrigerants are calculated using Coolprop. Using these models, the influence of the time variable heat sources and heat sinks, which depend on variable outside climate conditions and indoor temperature conditions, on the performance characteristics is investigated. Moreover, on/off control and variable speed control are analyzed as control strategies for demand side management to respond to intermittent renewable energy generation, taking advantage of the thermal inertia of the building and energy storage. The results show the COP dependence on the type of refrigeration/heat pump, temperature lift, outside climate conditions, inside temperature conditions, compressor efficiency, heat transfer conditions in the evaporator and the condenser, refrigerant thermodynamic properties, and thermodynamic cycle characteristics. The water-water refrigeration/heat pumps can reach the highest COP (COP>7). They have higher operational flexibility because the water can also be a medium for heating and cooling storage. The COP of air-air refrigeration/heat pumps strongly depends on outside climate conditions. For extreme winter climate conditions, when the heating demand is large, the COP is low (COP<3) and the heating capacity of the air-air refrigeration/heat pump decreases. However, water accessibility is a constraint for the wider application of water-water refrigeration/heat pumps. This can be overcome with the 5^th generation of district heating and cooling. The COP of the decentralized plants is high because the evaporation temperature is high (heat pump) and the condensing temperature is low (refrigeration system). Also, the COP of the central plant is high because the temperature lift is low. The high COP and wide operational flexibility make water-water refrigeration/heat pumps an asset in the energy transition and their wider applicability is facilitated by the development of the 5^th generation district heating and cooling systems.