Performance evaluation and optimal design of supermarket refrigeration systems with supermarket model "SuperSim", Part I: Model description and validation

This is the post-print version of the final paper published in International Journal of Refrigeration. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2010 Elsevier B.V.Conventional supermarket refrigeration systems are responsible for considerable CO2 emissions due to high energy consumption and large quantities of refrigerant leakage. In the effort to conserve energy and reduce environmental impacts, an efficient design tool for the analysis, evaluation and comparison of the performance of alternative system designs and controls is required. This paper provides a description of the modelling procedure employed in the supermarket simulation model ‘SuperSim’ for the simulation of the performance of centralised vapour compression refrigeration systems and their interaction with the building envelope and HVAC systems. The model which has been validated against data from a supermarket has been used for the comparison of R404A and CO2 refrigeration systems and the optimisation of the performance of transcritical CO2 systems. These results are presented in Part II of the paper.DEFR

The development and calibration of a generic dynamic absorption chiller model

Although absorption cooling has been available for many years, the technology has typically been viewed as a poorly performing alternative to vapour compression refrigeration. Rising energy prices and the requirement to improve energy efficiency is however driving renewed interest in the technology, particularly within the context of combined cooling, heat and power systems (CCHP) for buildings. In order to understand the performance of absorption cooling, numerous models are available in the literature. However, the complexities involved in the thermodynamics of absorption chillers have so far restricted researchers to creating steady state or dynamic models reliant on data measurements of the internal chiller state, which require difficult-to-obtain, intrusive measurements. The pragmatic, yet fully-dynamic model described in this paper is designed to be easily calibrated using data obtained from the measurements of inflows and outflows to a chiller, without resorting to intrusive measurements. The model comprises a series of linked control volumes featuring both performance maps and lumped mass volumes, which reflect the underlying physical structure of the device. The model was developed for the ESP-r building simulation tool. This paper describes the modelling approach, theory and limitations, along with its calibration and the application of the model to a specific example

Energy simulation of climatic wind tunnel plant

The Climatic Wind Tunnel (CWT) is a facility used by the motor industry to test vehicles under climatic extremes without the need for expensive overseas test programs. This work focuses on the application of computer simulation to the Heating Ventilation and Air Conditioning (HVAC) plant that makes up a CWT facility. The objective being to reduce its operational costs through the identification of energy saving operational strategies. When in operation the CWT has a peak power consumption of 3MW. The implementation of any measures that would reduce this peak load would give rise to considerable savings in the operating costs of the facility. Computer simulation is an accepted technique for the study of systems operating under varying load conditions. Simulation allows rapid analysis of different strategies for operating plant and the effectiveness of achieving the desired effect without compromising the buildings performance. Models for the components of the CWT have been developed and coded in Neutral Model Format. These models have then been linked together in a modular simulation environment to give a model of the complete plant. The CWT plant naturally decomposesin to four major subsystems these being the test chamber, the soakroom, air make-up and refrigeration system. Models of all the primary and secondary HVAC plant are described as is how they constitute the systems that make up the CWT. Validation tests for individual components as well as for the systems have been carried out. To illustrate the potential of the application of computer simulation into finding improved modes of operation that would reduce the energy consumption of the facility, four studies have been carried out. The studies involve the possibility of scheduling the operation of condenser fans as a function of refrigeration load and outside ambient temperature, methods for the pre-test conditioning of a vehicle, a reduction in the secondary refrigerant flow temperature and an increase in the thickness of the insulated panels from which the facility is constructed. The studies carried out showed that there was potential for moderate energy savings to be made in the operation of the facility and that extended simulation runs would allow for the in-depth assessment of a large range of possible modes of plant operation in order to identify the areas where the greatest savings are possible

Dynamic Simulation of Household Refrigerators: Numerical Model and Experimental Comparison

This work presents a dynamic model to simulate a whole household refrigeration unit taking into account both the refrigeration cycle itself and the refrigerated compartments network. The methodology implemented to achieve the transient simulation of the whole system combines a steady-state approach for the refrigerating cycle loop with a transient approach for the refrigerated compartments loop. Both loops are solved at each time step (the linking boundary conditions for the refrigerating cycle and the compartments network are the air temperature of the evaporator chamber and the heat generated by the evaporator, respectively). The numerical infrastructure implemented to simulate the whole system and its elements is described in [1]. On one hand, the refrigerating cycle loop includes appropriate numerical models for the main components, namely, hermetic compressor, wire-and-tube condenser, non-adiabatic capillary tube [2], and finned-tube evaporator. In addition, the receiver located at the outlet position of the evaporator, is also considered and modeled according to [3]. On the other, the refrigerated compartments loop is made up of connected chambers and a damper to regulate the cold air flow going to the refrigerator and freezer. The transient solution of the system includes two important features: i) a numerical model for the refrigerating cycle when the compressor is turned off, and ii) a control system to regulate the compartments temperatures by means of the damper position and the compressor working condition. In the first part of this work the main details of the resolution procedure and the numerical model of both the whole system and all its components are given. In the second part a set of parametric studies to analyse the influence of specific aspects of the main elements on the refrigerating cycle is carried out, namely, arrangements of fins and tubes in the evaporator, non-adiabatic capillary tube geometrical configurations, and gap between wire-and-tube condenser and rear wall. The trends of the numerical results are compared against experimental data at similar conditions. In the last section, an illustrative numerical case including most of the model features is shown in order to see the model potential. REFERENCES [1] N. Ablanque, C. Oliet, J. Rigola, O. Lehmkuhl, C.D. Pérez-Segarra,“Modular Simulation of Vapour Compression Systems with an Object-Oriented Tool”, International Refrigeration and Air Conditioning Conference at Purdue, 2377, Purdue, IN, USA, 2012. [2] N. Ablanque, J. Rigola, C.D. Pérez-Segarra, A. Oliva, “Numerical simulation of capillary tubes. Application to domestic refrigeration with isobutane”, International Refrigeration and Air Conditioning Conference at Purdue, 2377, Purdue, IN, USA, 2010. [3] A. Sadurni, Numerical Analysis and Experimental Studies on Vapour Compression Refrigerating Systems. Special Emphasis on Different Cycle Configurations. PhD Thesis. Universitat Politècnica de Catalunya, Terrassa, Spain, 2012

Evaluation of Supermarket Energy Use and Emissions with Various Technology Options

In this paper, an operational supermarket in the UK has been selected to be modelled by the previously developed supermarket energy simulation software ‘SuperSIM’. Detailed information of the supermarket and model development procedures are explained. The model was previously validated through comparisons with site measurements of space air temperature and humidity and energy consumptions. It is therefore used to simulate, quantify and evaluate supermarket energy performance at various technology options in terms of heat recovery from refrigerant discharge, high efficiency condensers and evaporators and store locations etc

HVAC system simulation: overview, issues and some solutions

Integrated performance simulation of buildings’ heating, ventilation and air-conditioning (HVAC) systems can help in reducing energy consumption and increasing occupant comfort. Recognizing this fact, in the last forty years many tools have been developed to help achieving this goal. In this paper we introduce a categorization of these tools with respect to which problems they are meant to deal with and summarize current approaches used for modelling (i) HVAC components, (ii) HVAC control and (iii) HVAC systems in general. Further in this paper, we list issues associated with applications of HVAC modelling and simulation. Finally, we present and discuss co-simulation as one of solutions that can alleviate some of the recognized issues

Supermarket refrigeration systems for demand response in smart grids

With an increasing share of intermittent renewable energy sources in the electrical grid, the need for adapting the demand to the available supply of electricity becomes increasingly important. Within this thesis, the demand response capacity by supermarket refrigeration systems are investigated and methods for enabling it is developed.Article 1 explores the temperature control system in depth, concluding that the majority (80.5 %) of return air temperature sensors in RDCs were located in an area where a thermal gradient interfere with the perceived temperature, i.e. the temperature readings falsely indicated a higher return air temperature than the actual mean temperature of the passing air. The issue is analysed in detail and mitigated through a strategic re-positioning of the affected temperature sensors.Article 2 presents a computationally efficient yet accurate dynamic hygro-thermal model of an RDC with the capability to include effects of door openings. Thus, the model contributes to enabling demand response by supermarkets as it could provide the forecasts of the necessary temperature constraints, limiting the duration for which the supermarket could attend to a demand response request.Article 3 presents a field study where wireless gyroscopes were attached to the RDC doors in an operational supermarket to record the speed, duration, angle and frequency that the doors are operated at. Novel insights in significant differences in behaviour between medium and low temperature RDCs could be concluded.Article 4 presents a method for the thermal characterisation of RDCs based on an adaption of the Co-Heating methodology. The method evaluates infiltration rates within the 10 % limit compared with the condensate collection method. In addition, data on thermal performance, such as the heat transfer coefficient for the envelope and its thermal inertia, can be measured in a systematic way. The thesis together with the four appended articles presents a suite for the evaluation of temperature development in refrigerated display cabinets in operational supermarkets, which represents the main constrain for the demand response capacity

Modelling and data validation for the energy analysis of absorption refrigeration systems

Data validation and reconciliation techniques have been extensively used in the process industry to improve the data accuracy. These techniques exploit the redundancy in the measurements in order to obtain a set of adjusted measurements that satisfy the plant model. Nevertheless, not many applications deal with closed cycles with complex connectivity and recycle loops, as in absorption refrigeration cycles. This thesis proposes a methodology for the steady-state data validation of absorption refrigeration systems. This methodology includes the identification of steady-state, resolution of the data reconciliation and parameter estimation problems and the detection and elimination of gross errors. The methodology developed through this thesis will be useful for generating a set of coherent measurements and operation parameters of an absorption chiller for downstream applications: performance calculation, development of empirical models, optimisation, etc. The methodology is demonstrated using experimental data of different types of absorption refrigeration systems with different levels of redundancy.Los procedimientos de validación y reconciliación de datos se han utilizado en la industria de procesos para mejorar la precisión de los datos. Estos procedimientos aprovechan la redundancia enlas mediciones para obtener un conjunto de datos ajustados que satisfacen el modelo de la planta. Sin embargo, no hay muchas aplicaciones que traten con ciclos cerrados, y configuraciones complejas, como los ciclos de refrigeración por absorción. Esta tesis propone una metodología para la validación de datos en estado estacionario de enfriadoras de absorción. Estametodología incluye la identificación del estado estacionario, la resolución de los problemas de reconciliación de datos y estimación de parámetrosy la detección de errores sistemáticos. Esta metodología será útil para generar un conjunto de medidas coherentes para aplicaciones como: cálculo de prestaciones, desarrollo de modelos empíricos, optimización, etc. La metodología es demostrada utilizando datos experimentales de diferentes enfriadoras de absorción, con diferentes niveles de redundancia