Food retail with large supermarkets consumes significant amounts of energy. The environmental impact is also significant because of the indirect effect from CO2 emissions at the power stations and due to the direct effect arising from refrigerant leakage to the atmosphere. The application of trigeneration (local combined heat, power and refrigeration) can provide substantial improvements in the overall energy efficiency over the conventional supermarket energy approach of separate provision of electrical power and thermal energy. The use of natural refrigerants such as CO2 offers the opportunity to reduce the direct impacts of refrigeration compared to conventional systems employing HFC refrigerants that possess high global warming potential. One approach through which the overall energy efficiency can be increased and the environmental impacts reduced, is through the integration of trigeneration and CO2 refrigeration systems where the cooling generated by the trigeneration system is used to condense the CO2 refrigerant in a cascade arrangement. This research project investigates experimentally and theoretically, through mathematical modelling and simulation, such a system and its potential application to supermarkets. A small size CO2 refrigeration system for low and medium food temperature applications was designed and constructed to enable it to be integrated with an existing trigeneration system in the refrigeration laboratory at Brunel University to form an integrated trigeneration and CO2 refrigeration test facility. Prior to the construction, the design of the system was investigated using mathematical models developed for this purpose. The simulations included the CO2 refrigeration system, CO2 evaporator coils and the integration of the trigeneration and CO2 refrigeration systems. The physical size of the design and component arrangement was also optimised in a 3D AutoCAD model. A series of experimental tests were carried out and the results showed that the medium temperature system could achieve a very good COP, ranging from 32 to 60 due to the low pumping power requirement of the liquid refrigerant. The low temperature system performed with average steady state COP of 4, giving an overall refrigeration system COP in the range between 5.5 and 6. Mathematical models were also developed to investigate the application of the integrated trigeneration and CO2 refrigeration system in a case study supermarket. The models were validated against test results in the laboratory and manufacturers’ data. The fuel utilisation efficiency and environmental impacts of different trigeneration and CO2 refrigeration arrangements were also evaluated. The results indicated that a system comprising of a sub-critical CO2 refrigeration system integrated with a trigeneration system consisting of a micro-turbine based Combined Heat and Power (CHP) unit and ammonia-water absorption refrigeration system could provide energy savings of the order of 15% and CO2 emission savings of the order of 30% compared to conventional supermarket energy systems. Employing a trigeneration system with a natural gas engine based CHP and Lithium Bromide-Water sorption refrigeration system, could offer energy savings of 30% and CO2 emission savings of 43% over a conventional energy system arrangement. Economic analysis of the system has shown a promising payback period of just over 3 years compared to conventional systems.

El sector de pasta i paper és considerat un dels set sectors industrials més intensius en consum energètic. La producció i consum d'electricitat i de vapor esdevenen les fonts majoritàries d'emissions de gasos d'efecte hivernacle en aquest sector industrial. Les fàbriques papereres poden assolir objectius de reducció d'emissions mitjançant reducció en origen (substitució de combustibles, introducció d'energies renovables) o bé a partir de mesures d'eficiència energètica en el propi procés. En aquest context, s'ha desenvolupat un mètode de distribució d'emissions que permet assignar a cada unitat d'operació del procés paperer, el seu grau de responsabilitat en emissions. També s'han avaluat diferents mètodes de càlcul de factors d'emissió de vapor i electricitat, tant per plantes de cogeneració com per sistemes individuals. A partir d'aquesta avaluació s'han proposat nous mètodes alternatius als analitzats. Aquests mètodes i els factors d'emissions s'han aplicat a dues fàbriques papereres catalanes. / Pulp and paper sector is considered one of the seven industrial sectors with a higher energy intensive profile. Power and steam production and consumption are the main responsible for green house gas emissions of this industrial activity. Paper industries can achieve reductive emission targets by considering emissions origin (replacing fuels, aplying renewable energies) as well as improving energy efficiency of the process itself. An emission allocation tool has been developed with the purpose of approaching to each unit operation of the papermaking process its related emissions share. In addition, energy-emission factors regarding power and steam generation in combined heat and power plants and in single heat and power systems have been evaluated. Some new methods for calculating different emission factors have been proposed after the analysis. Two Catalan paper mills have been used as case-studies to apply, both allocation method and emission factors.