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Energy benefit assessment of various refrigeration systems integrated with HVAC units in shopping malls
Full text linkShopping malls are among the most energy intensive commercial buildings, mainly due to heating, air conditioning and refrigeration plants. In recent years new innovative solutions have been employed in both the building and the plants, in order to reduce as much as possible the energy requirement and to increase the energy conversion efficiency of the systems. This practice has been further motivated by the need for using low environmental impact refrigerants, thus giving place to a widespread renovation of plants. The growing awareness of the environmental protection and the strong push by the European Union towards the use of natural refrigerants has been promoting the spread of carbon dioxide as working fluid.
The CO2 refrigeration units operating in cold climates perform better than solutions using synthetic and not environmentally friendly refrigerants, while in mild and warm climates, due to the low critical temperature of the carbon dioxide, transcritical operations in R744 systems can commonly take place, increasing substantially the energy consumption. On the other hand, the high temperatures reached by the CO2 in the high pressure heat exchanger potentially allow recovering a large amount of heat at different temperature levels according to the supermarket needs. This leads to further opportunities for the spread of CO2 as refrigerant in mild and warm climates. Heat recovery and the integration with the heating, ventilating and air conditioning (HVAC) units make the CO2 competitive as refrigerant also in climates characterized by high outdoor temperatures.
In this perspective, dynamic simulations of complex systems and control strategies play a crucial role in the performance assessment and system management.
This work analyses the energy saving potential generated by the heat recovery from carbon dioxide refrigeration systems in favour of the heating system of the building and by the integration of the refrigeration systems with the supermarket HVAC units in shopping malls located in mild and warm climates.
A comprehensive model of the commercial building, the refrigerated food storage equipment, the HVAC units and the refrigeration systems is developed.I centri commerciali sono tra i servizi più energivori, principalmente a causa degli elevati consumi per il riscaldamento, per il condizionamento dell’aria e per la frigoconservazione. Negli ultimi anni sono state adottate molteplici soluzioni innovative sia negli edifici che negli impianti con lo scopo di ridurre il più possibile la domanda di energia e di aumentare l’efficienza energetica dei diversi sistemi. Ciò è stato inoltre motivato dalla necessità di utilizzare refrigeranti a basso impatto ambientale, dando luogo a un diffuso rinnovamento degli impanti. La crescente consapevolezza ambientale e la forte spinta dell’Unione Europea verso l’utilizzo di refrigeranti naturali hanno promosso la diffusione dell’anidride carbonica come fluido di lavoro.
I sistemi di refrigerazione a CO2 in climi freddi forniscono prestazioni migliori rispetto alle tradizionali soluzioni che utilizzano refrigeranti sintetici e non eco-compatibili, mentre in climi miti e caldi, a causa della bassa temperatura critica dell’anidride carbonica, i sistemi a R744 lavorano frequentemente in condizioni transcritiche, aumentando considerevolmente i consumi. D’altra parte, le alte temperature raggiunte dalla CO2 negli scambiatori di alta pressione permettono potenzialmente il recupero di grandi quantità di calore a differenti livelli di temperatura in accordo alle diverse esigenze dei supermercati. Questo genera ulteriori opportunità per la diffusione nei climi miti e caldi dell’anidride carbonica come refrigerante. Il recupero di calore e l’integrazione con le unità HVAC possono infatti rendere competitiva sia energeticamente che economicamente la CO2 come refrigerante anche in climi caratterizzati da elevate temperature esterne.
In questa prospettiva, la simulazione dinamica di sistemi complessi e le strategie di controllo giocano un ruolo fondamentale nella valutazione delle performance e nella gestione dei diversi componenti.
Questo lavoro analizza i potenziali risparmi energetici ottenibili dal recupero di calore da sistemi di refrigerazione ad anidride carbonica in favore degli impianti di riscaldamento e dall’integrazione di tali sistemi con le unità HVAC per supermercati e centri commerciali situati in climi miti e caldi.
A tale scopo sono stati sviluppati modelli di simulazione completi dell’edificio commerciale, degli apparecchi per lo stoccaggio e la conservazione degli alimenti, delle unità per il riscaldamento e la climatizzazione dell’aria e dei sistemi di refrigerazione
Valutazione delle prestazioni di macchine frigorifere a CO2 per applicazioni commerciali in climi caldi
No full textLe prestazioni delle macchine frigorifere a CO2 sono notevolmente influenzate dalla temperatura dell’aria esterna. La configurazione base, infatti, si caratterizza per efficienze molto più basse rispetto alle soluzioni attualmente impiegate nei climi caldi. Al fine di migliorarne le prestazioni, differenti espedienti tecnologici sono stati recentemente proposti. In questo articolo, i coefficienti di prestazione (COP) ed i consumi energetici annuali di diverse soluzioni impiantistiche a CO2 vengono comparati a quelli di un sistema convenzionale ad espansione diretta a R404A. Tali valutazioni sono state implementate considerando le tipiche condizioni operative di un supermercato localizzato in diverse città dell’Europa meridionale
Modelling commercial refrigeration systems coupled with water storage to improve energy efficiency and perform heat recovery
Full text linkA 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 environment, taking
into account the hourly weather data and calculating the hourly cooling load demand from
display cabinets and cold rooms equipment. New types have been written to describe display
cabinets and cold rooms, CO2 refrigerating units and a particular water store.
Simulations consider a simple double compression cycle with liquid receiver, and other
options among which an auxiliary compressor. Results show that CO2 plants are feasible
and energetically acceptable in mild climates, provided that improvements to standard cycle
are adopted. Furthermore, heat recovery can be effectively performed through the employment
of a heat storag
Energy and environmental comparison of commercial R744 refrigeration systems operating in warm climates
No full textCarbon dioxide (CO2, R744) is an environmentally friendly refrigerant, which is widely used in supermarket refrigeration systems located in cold weather sites. Its use at high outdoor temperatures still requires some additional investigations to accomplish performance similar to the one obtained by employing the conventional working fluids.
This paper deals with the theoretical comparison in terms of both annual energy consumption and Total Equivalent Warming Impact (TEWI) of different commercial R744 refrigeration cycles operating in five different warm climates. An innovative CO2 direct expansion (DX) configuration, which serves both the medium temperature (MT) load and the low temperature (LT) one, is also considered. Taking into account the running modes of a typical European supermarket and a R404A multiplex configuration as the baseline, the results showed that enhanced R744 refrigeration technologies are capable of dropping the energy consumption and the TEWI by at least 2.8% and 31.1%, respectively
Performance Evaluation of a R744 Booster System for Supermarket Refrigeration, Heating and DHW
No full textCarbon 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 cooler) to cover domestic hot water (DHW) and heating needs.
The investigated solution is a R744 booster refrigeration system operating in mild climates, which provides the selected supermarket with DHW and heating, besides satisfying the cooling load required by display cabinets and cold rooms. To meet the full heating load of the building in any operating conditions, an additional air-cooled evaporator can be used as a supplemental heat source, driving to an increment in the total energy consumption.
This paper investigates a suitable control strategy for the chosen system in order to minimize the consumption and, contemporary, supply both the cooling and heating loads
Water storage to improve the efficiency of CO2 commercial refrigeration systems
No full textCarbon 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 application of CO2 also to mild climate conditions, through modifications of the refrigerating cycle and the adoption of various innovative configurations. Quite often such configurations require significant extra costs or involve the adoption of solutions not yet well established in the market. In some cases the promotion of interactions between the refrigeration systems and other systems available in the building could allow for the exploitation of simple solutions which could be easily adopted with low extra costs.
In this paper a basic CO2 transcritical/subcritical commercial refrigeration system is considered, applied to cold rooms and display cabinets in a supermarket located inside a large shopping mall. Subcooling of the refrigerant is performed, taking advantage of a large fire prevention water tank.
The whole refrigeration system has been modelled in Trnsys environment. Simulations have been carried out taking into account the hourly weather data and the daily profile of the cooling load demand from the refrigerated food storage equipment.
Different configurations are examined, for the best exploitation of this cold storage. The technical feasibility of this solution is investigated
Supermarket refrigeration and air conditioning systems integration via a water storage
No full textOne 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 subcooling the refrigerant at the exit of the gas cooler is very interesting when
a cold storage is available, or when the rejected heat may be recovered for other thermal systems in the
supermarket. In this paper the exploitation of a large fire prevention tank as a condenser/subcooler for a
supermarket CO2 booster refrigeration system and as a heat source for a heat pump for the HVAC system is
investigated. The whole system is modelled in the Trnsys environment and the effects of the thermal capacity
on the energy efficiency are compared with the case of the two systems running separately. The energy savings
range from about 3% to more than 5% at two different locations in Northern Italy
Energy benefit assessment of a Water Loop Heat Pump system integrated with a CO2 commercial refrigeration unit
Full text linkThe 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 Potential (GWP) refrigerants, and the indirect impact on the environment related to high electrical energy consumption, make shopping malls not sustainable buildings.
This paper analyses the energy saving potential of integrated supermarket air conditioning and refrigeration systems using a Water Loop Heat Pump system (WLHP), where a water loop is used as a heat source/sink for a number of electric reversible heat pumps which provide climate control on the thermal zones. A basic CO2 booster commercial refrigeration system, applied to cold rooms and display cabinets, is considered. Heat recovery from the refrigeration circuit is performed in the heating season, while in the cooling season a dry cooler on the water loop allows heat rejection to outdoors.
A comprehensive model of a commercial building, HVAC and refrigeration integrated systems is presented. The building and all systems are modelled in the Trnsys environment taking into account the hourly weather data, the simulated daily profiles of the cooling and heating load demand and the request from refrigerated food storage equipment. Such a model allows a thorough understanding of the potential for energy savings with heat recovery solutions. This work is developed in the framework of CommONEnergy, an EU project funded by the European Community within the Seventh Framework Programme (FP7/2007-2013) that aims at reducing energy consumption in shopping malls
Energy analysis of a transcritical CO2 supermarket refrigeration system with heat recovery
Full text linkCarbon 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 substantially. On the other hand, the high temperatures reached by the CO2 in the high pressure heat exchanger (gas cooler) potentially allow recovering a large amount of heat at different temperature levels according to the supermarket needs.
The paper deals with the energy performance evaluation of a R744 refrigeration system, which provides the selected supermarket with DHW and heating, besides satisfying the cooling load required by the refrigerated and frozen food storage equipment. The system is equipped with an additional air-cooled evaporator which can be used as a supplemental heat source, to increase the amount of heat recovered and meet the full heating demand of the building. Different control strategies are examined in order to minimize the electric consumption and, contemporary, maximize the heat recovery
Overfed Evaporators and Parallel Compression in Commercial R744 Booster Refrigeration Systems– an Assessment of Energy benefits
No full textThe entry into force of the EU F-Gas Regulation 2014 pushes European Countries to use natural refrigerants. Carbon dioxide (R744) is one of the most promising long-term alternatives to the currently employed refrigerants in commercial refrigeration. On the other hand, the use of CO2 supermarket refrigeration systems in warm climates requires specific technical solutions to make them competitive with conventional HFC-based plants. In the European market, different layouts have been currently proposed, which have been mainly derived from the basic booster configuration.
In this paper, the performance of a commercial CO2 refrigeration solution employing medium temperature (MT) overfed evaporators, a CO2 refrigeration configuration using parallel compression and the system which combines both of the previously technologies were theoretically compared. Three different warm climate locations were selected, i.e. Rome (Italy), Valencia (Spain) and Seville (Spain). The results showed that the benefits deriving from a higher evaporating temperature in the MT display counters, allowed by overfed evaporators, outweighed those related to parallel compression. Furthermore, the investigated R744 refrigerating plants performed an annual energy saving ranging from 2.9% to 12.3% over a R404A multiplex refrigeration system. The use of a de-superheater on the part of the combined solution led to an additional drop in the annual electricity consumption by 2.3-2.6%
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