Paola D'Agaro

University of Udine | UNIUD · Department of Electrical, Management and Mechanical Engineering

A real case of a supermarket where a CO2 refrigerating plant also supplies heating, air conditioning and hot water is considered. Ice thermal energy storage (ITES) is used both as latent storage in summer and as sensible thermal energy storage (TES) in winter to partially cover the space cooling/heating load of the supermarket. In particular, it al...

In this work, the utilization of the supervision system of a five-story hotel located in Northern Italy as tool to calibrate and validate a building energy model (BEM) is evaluated. The BEM is created using the TRNSYS simulation environment with the aim to develop a digital twin, to study the energy consumption of the building-HVAC system. The proc...

Building energy simulations are important to assess the performance of buildings and to design solution aimed at reducing energy consumption and carbon emissions. Many software perform these simulations, focusing on systems operations and energy losses and gains. When it comes to modelling historical buildings, the simulations could be also used to...

Building energy simulations are a key tool to design high performance buildings capable of facing the future challenges, to help reaching the emissions reduction targets. Currently, thermal properties of materials used in most building energy simulations are assumed to be constant and not dependent from moisture content and temperature. Heat and mo...

The cooling load of a commercial refrigeration system is affected by the operating conditions of the refrigerated display cabinets and cold rooms, mainly through their mutual interactions with the indoor environment in terms of temperature and humidity. In this paper, the effects of cooling load profiles in the prediction of the annual energy use a...

The electrical energy demand of an HVAC plant can be better managed by using latent thermal energy storage when time-of-use tariffs or peak tariffs are in force, in a view of Demand Side Management of the electrical grid. Nonetheless, air conditioning systems show a marked use of electrical power during the day, and the peak in the cooling load mos...

The electrical energy demand of an HVAC plant can be better managed by using latent thermal energy storage when time-of-use tariffs or peak tariffs are in force, in a view of Demand Side Management of the electrical grid. Nonetheless, air conditioning systems show a marked use of electrical power during the day, and the peak in the cooling load mos...

Transcritical CO2 refrigeration systems for supermarkets are more and more integrated to DHW production, space cooling & heating. In CO2 integrated solutions, the thermal loads of supermarket buildings are fully covered by the refrigeration system, but advantages in terms of total investment and running costs need to be carefully estimated. They ar...

Transient building energy simulations are powerful design tools that are used for the estimation of HVAC demands and internal hygrothermal conditions of buildings. These calculations are commonly performed using a (often dated) typical meteorological year, generated from past weather measurements excluding extreme weather conditions. In this paper...

Heat and Moisture Transfer (HMT) simulations are used to evaluate moisture related damage risks in building envelopes. HMT simulations are commonly performed accepting the hypothesis of not considering the moisture hysteresis of materials. The results of HMT simulation of a timber wall with hysteresis are presented, and compared to the results of t...

An ice thermal energy storage is adopted in the HVAC plant of a supermarket, to shave peaks in electricity use. Ice is formed at night-time by employing the commercial refrigeration system, which is considerably partloaded during the shop closing time. During daytime, the thermal storage is discharged and operated in parallel to a water chiller, to...

Use of Dedicated Mechanical Subcoolers gives rise to the need of an optimisation process involving gas cooler pressure, activation and setpoint temperature values, subcooling degree and subcooler size, with the aim of further improving the energy efficiency while considering costs. In this paper a thermoeconomic analysis is performed on a commercia...

Use of Dedicated Mechanical Subcoolers gives rise to the need of an optimisation process involving gas cooler pressure, activation and setpoint temperature values, subcooling degree and subcooler size, with the aim of further improving the energy efficiency while considering costs. In this paper a thermoeconomic analysis is performed on a commercia...

A numerical procedure for the simulation of both fogging and the defogging process on the glass door of a vertical refrigeration display cabinet for chilled food is presented. The large scale problem within the cabinet (convective air flow and heat transfer, moisture mass transport, unsteady conduction through a multi-glazed door) is modelled via a...

Dedicated Mechanical Subcooling (DMS) is one of the most investigated and effective strategies applied to increase the performance of CO2 commercial refrigeration systems in transcritical operation. Further performance benefits can be obtained by a reduction of the gas cooler pressure of the main cycle at transcritical conditions. In this work the...

The use of hybrid surfaces, alternating hydrophobic and hydrophilic (or less-hydrophobic) areas, has been recently proposed as a valuable tool for dropwise condensation performances enhancement. The hydrophilic region, in particular, is designed in order to promote the removal of the droplet from the hydrophobic region, reducing their average size...

A Lagrangian model following the history of every droplet belonging to an evolving droplets population, originally developed to simulate pattern evolution in the framework of in-flight icing phenomenon, is used in order to simulate dropwise condensation over different shaped micro-structured surfaces. Both the mechanical and the thermal energy bala...

Subcooling methods at the exit of the gas cooler in transcritical CO2 commercial refrigeration systems have been studied in the recent years showing that overall remarkable improvements can be obtained. Another strategy that results efficient is the use of evaporative systems at the gas cooler (adiabatic cooling) as it allows to significantly reduc...

Accounting for about 17% of the overall electricity consumption worldwide, the refrigeration sector requires improvements in energy reduction and management. Demand side management (DSM) could be adopted to improve the overall system energy efficiency. In this work, a CO2 commercial refrigeration system coupled with different cold thermal energy st...

A langrangian-based phenomenological model, following the evolution of the individual droplets nucleating at random positions, is applied to the simulation and optimization of hybrid, mixed hydrophobic and hydrophilic surfaces. The proposed mathematical model was originally developed to simulate droplets pattern evolution in the framework of in-fli...

A fully instrumented CO 2 trans-critical booster system with parallel compression, in operation in a small size supermarket in northern Italy, made available measured data that allowed monitoring its performance. The entire refrigeration system of the supermarket, i.e. the Commercial Refrigerating Unit, the refrigerated display cabinets and cold ro...

Supermarkets are intensive energy consumers because of a high electricity demand, mainly due to refrigeration utilities. Thus, in this work a supermarket integrated HVAC, refrigeration and water loop heat pump (WLHP) system was analyzed according to a demand side management approach, adopting a demand response strategy coupled with real-time pricin...

Demand side management (DSM) strategies can be used to reduce customers' demand at peak times, change the timing of end-use consumption from high to low-cost periods and increase consumption during off-peak periods. They can be implemented by using the energy flexibility available in the final users' applications, energy storages or control systems...

In warm climates carbon dioxide (R744) refrigeration systems are known to perform worse because of the transcritical operation which occurs for a large part of the year, increasing substantially their energy use. On the other hand, the high discharge temperature potentially allows recovering a large amount of heat at various temperature levels. Thi...

Demand side management (DSM) strategies can be used to reduce customers' demand at peak times, change the timing of end-use consumption from high to low-cost periods and increase consumption during off-peak periods. They can be implemented by using the energy flexibility available in the final users' applications, energy storages or control systems...

Employing natural fluids in refrigerating plants at warm climate conditions sometimes impacts negatively on the system performance. Ejectors can play a key role in configurations aiming at improving the efficiency of such systems, however their geometry has to be optimized in order to gain the best benefit. Scope of this work is a numerical investi...

Demand side management (DSM) can be defined as a set of measures adopted to modify customers’ energy demand with the aim of improving the efficiency of the overall energy system. Indeed, DSM strategies can be used to reduce customers’ demand at peak times, reduce energy consumption seasonally/yearly, change the timing of end-use consumption from hi...

During the refurbishment of a supermarket in northern Italy, the HFC refrigeration plant has been replaced by a new CO2 transcritical system. A deep synergy has been favoured with the HVAC system, by allowing mutual heat exchanges at various temperature levels. Simulations have been performed at the design stage, with a TRNSYS based tool and in-hou...

The improvement of energy efficiency and the use of environmentally friendly working fluids are key elements of current European policies. Supermarkets are intensive energy consumers and approximately the 40% of their annual energy consumption is for refrigeration. Direct emissions of greenhouse gases associated with the use of high Global Warming...

The improvement of energy efficiency and the use of environmentally friendly working fluids are key elements of current European policies. Supermarkets are intensive energy consumers and approximately the 40% of their annual energy consumption is for refrigeration. Direct emissions of greenhouse gases associated with the use of high Global Warming...

Carbon dioxide (R744) is widely used as refrigerant in supermarkets located in cold weather sites thanks to its negligible environmental impact and its favourable thermo-physical properties. Due to its low critical temperature, transcritical operations in CO2 refrigeration systems can commonly take place, increasing the energy consumption substanti...

A basic CO2 transcritical/subcritical commercial refrigeration system is considered, applied to cold rooms and display cabinets in a supermarket. Subcooling of the refrigerant or heat recovery from condensation can be performed, taking advantage of a large fire prevention water tank. The whole refrigeration system is modelled in a TRNSYS environmen...

Carbon dioxide is an eco-friendly refrigerant which is non-flammable and non-toxic. Due to its low critical temperature, transcritical operations in CO2 refrigeration systems can commonly take place. In these conditions, favourable thermo-physical properties of R744 allow heat recovery at high temperature in the high pressure heat exchanger (gas co...

One of the most challenging targets for the Commercial Refrigeration sector nowadays is spreading the use of pure CO2 systems in mild climate countries. In recent years several solutions have been proposed in order to improve the performance of CO2 transcritical cycles. Among these improvements, the reduction of the discharge pressure by means of s...

Energy savings can be achieved not only with development of display cabinets and refrigeration systems, but also with a careful integration with the HVAC plant, heat recovery, combined heat and power generation and tri-generation. Various measures can be implemented both as retrofit for existing plants and as improved solutions for new designs, to...

Carbon dioxide is being more and more widely used in commercial refrigeration, due to its negligible environmental impact. However up to now its application as the only refrigerant is especially devoted to cold climates, which allow for the best exploitation of this refrigerant. Several solutions are being identified to extend a convenient applicat...

The present paper is aimed at the modeling of a continuous film breakup into individual rivulets, leading to the formation of dry patches on the substrate surface. Following an approach already successfully applied to the prediction of still/moving droplet configuration, we attempt to model the details of a single possible film breakup and its evol...

Decision makers in the supermarket chains ask with ever increasing strength for a comparison between different HVAC and refrigeration plant solutions, not only in terms of investment costs, but also of energy needs. The option of heat recovery from the refrigeration plant in favour of the HVAC system for space heating is being more and more conside...

Decision makers in the supermarket chains ask with ever increasing strength for a comparison between different HVAC and refrigeration plant solutions, not only in terms of investment costs, but also of energy needs. The option of heat recovery from the refrigeration plant in favour of the HVAC system for space heating is being more and more conside...

Decision makers in the supermarket chains ask with ever increasing strength for a comparison between different HVAC and refrigeration plant solutions, not only in terms of investment costs, but also of energy needs. The option of heat recovery from the refrigeration plant in favour of the HVAC system for space heating is being more and more conside...

Wholesales & Retail buildings represent 28% of the total non-residential building stock, accounting for approximately 157 Mtoe in 2005.Considering typical shopping malls high impact on modern society, the project addresses their transformation as lighthouses of energy efficient architectures and systems as well as assessment transparency. CommONEne...

A fully conjugate heat transfer analysis of gaseous flow, within slip flow regime, in short microchannel is presented. A Navier Stokes code, coupled with Maxwell and Smoluchowski slip and temperature jump model, is adopted. Due to the link between temperature and velocity field in highly compressible flows, results are presented for Nusselt number,...

A numerical model for the prediction of the build up of a moist air condensate layer is presented. The model simulates the process of birth, growth, coalescence and possible motion of each individual condensate droplet. Due to its computational intensity, such a kind of approach is not feasible for the simulation of complex configurations of indust...

A numerical analysis of conjugate heat transfer in coolant passages with arrays of pin fins is carried out. Uniform heat flow is applied externally to the base plate of the pins, which is thermally conducting. The base plate itself redistributes the applied heat flux, allowing energy flux to concentrate toward the pins. The effect of such a redistr...

In several heat exchange devices, phase transition occurs in a small region adjacent to the wall, and the secondary phase is present only in a thin layer running along the wall, allowing for decoupling between the fluid dynamic computation of the core flow and the numerical analysis of the secondary phase. This happens in finned dehumidifier, but a...

The present paper deals with the laminar forced convection in a parallel-plane channel, and is aimed to investigate the effect of conducting walls. On the external boundaries of the duct walls a thermal boundary condition is prescribed, such that the wall heat flux longitudinally varies with sinusoidal law. The local energy balance equation is writ...

High pressure drop and high length to hydraulic diameter ratios yield significant compressibility effects in microchannel flows, which compete with rarefaction phenomena at the smaller scale. In such regimes, flow field and temperature field are no longer decoupled. In presence of significant heat transfer, and combined with the effect of viscous d...

Three-dimensional laminar forced convection including steady-periodic transition is investigated up to periodic-chaotic transition in the fully developed region of coolant passages with staggered arrays of pin fins. Comparative examples concern overall pressure losses and heat transfer characteristics of circular, square and elliptical pins made of...

The present paper studies the conjugate heat transfer problem in a parallel-plane channel. Laminar and stationary forced convection is studied, with a boundary condition given by a temperature distribution on the external side of the channel wall, which undergoes a sinusoidal longitudinal change. The local energy balance equation is written with re...

Surface roughness may have a significant impact on microchannel performances, since at such a small scale it is nearly impossible to obtain an actual smooth surface. The numerical approach allows a detailed description of the surface imperfections; thus, we can easily separate roughness from other microscale effects. In this paper, roughness is mod...

A suite of routines for the prediction of environment moist condensation and evaporation on solid surfaces is presented. The physical problem requires the solution of the airflow field along a (cold) solid surface, the evaluation of the unsteady conduction through the solid itself, and the development of a suitable model for the heat and mass trans...

A numerical analysis of the flow field in rough microchannel is carried out with a finite volume compressible solver, including generalized Maxwell slip flow boundary conditions suitable for arbitrary geometries. Roughness geometry is modeled as a series of triangular obstructions. The relative roughness from 0% to 2.65% was considered. Because for...

The aim of this study was to compare the measured effectiveness of an air curtain device at different jet velocities against a three-dimensional (3-D) computational fluid dynamics (CFD) model. The air curtain device was not as wide as the entrance and had a geometry that encouraged 3-D flow. By carefully setting up the air curtain an effectiveness...

A numerical procedure for the simulation of fogging and defogging phenomena is presented and is applied to the prediction of the demisting process on the glass door of a refrigerated closed display cabinet.The physical problem depends on the flow field along the glass, both inside and outside the refrigerated cabinet, on the unsteady conduction thr...

The effectiveness of a 1.0m wide air curtain fitted over a 1.36m wide entrance to a cold store has been evaluated. It was shown that careful setting up of the air curtain (adjusting the jet velocity and angle) was needed, this achieved an effectiveness of 0.77 compared to the initial value of only 0.31 as set by the installer. An analytical model t...

A commercial CFD code has been employed to simulate the air flow pattern and the temperature distribution in a frozen food vertical display cabinet. At first the choice of solver parameters has been investigated in a 2D modelisation. 3D simulations have been then performed, and the effects of the cabinet length, of the warm air curtain and of longi...

A numerical analysis of three-dimensional flow structures in a nominally two-dimensional fin geometry is presented. A sinusoidal louvred fin is considered. The heat transfer enhancement is achieved by combining boundary layer interruptions and vortical structures induced by the corrugation of the base fin. The fin shape and pitch, as well as flow c...

A numerical procedure for the prediction of fogging and defogging phenomena is presented. The simulation involves the solution of an air flow field along a cold solid surface, the evaluation of the unsteady conduction through the solid itself, and a model for the heat and mass transfer within the thin water layer on the fogged surface. A suite of r...

Roughness effects on the heat transfer and pressure losses in microscale tubes and channels are investigated through a finite element CFD code. Surface roughness is explicitly modelled through a set of randomly generated peaks along the ideal smooth surface. Different peak shapes and distributions are considered; geometrical parameters are represen...

In retail premises, display cabinets play an important role in persuading the customer to buy food products, while satisfactorily preserving them. This is a complex task, because these two purposes are in some way conflicting.

The decrease of the air-side thermal resistance by adoption of variously interrupted and corrugated surfaces is a major aim in compact heat exchangers design. The current study presents a two-dimensional numerical analysis of flow field and heat transfer in two typical fin configurations: flat and wavy interrupted fins. Simulations are carried out...

Roughness effect on the heat transfer and pressure loss performances of microscale tubes and channels are investigated through a finite element CFD code. Surface roughness is explicitly modelled through a set of random generated peaks along the ideal smooth surface. Different peak shapes and distributions are considered; geometrical parameters are...

A three-dimensional numerical investigation of flow field and heat transfer in sine-wave crossed ducts is presented. Numerical simulations are carried out using a finite element procedure based on an algorithm which shares many features with the SIMPLER finite-volume method, and utilizes equal order pressure–velocity interpolation functions. Since...