Characterization of cooling loads in the wine industry and novel seasonal indicator for reliable assessment of energy saving through retrofit of chillers

The food sector is a major consumer of energy and growing efforts are being made in the search for solutions that will guarantee the efficient and sustainable use of energy resources. Among the different sectors, wineries are attracting particular interest due to the continuous growth of the global market and production. Surveys conducted in the winemaking sector have highlighted the importance of performing accurate energy audits and have identified the installation of efficient refrigeration systems as a promising solution in a variety of cases. Unfortunately, the savings achievable by efficient cooling technologies are often estimated using simplified approaches which do not take into consideration the actual operating conditions of the equipment typically variable on seasonal and daily bases. In this paper a novel bottom-up procedure is presented, aimed at developing reliable profiles for refrigeration and air-conditioning loads and at assessing the extent to which more efficient chilling units could contribute to reducing electricity consumption. The use of standard Seasonal Energy Efficiency Ratios is critically discussed and a novel customized indicator is proposed. The method is applied to a medium-scale winery producing still red and white wines and sparkling wines, for which only aggregated energy consumption data are available. After deriving detailed load profiles, it is proven that the use of standard seasonal indicators leads to 56.85% and 83.87% overestimation of potential energy savings, respectively, for low and medium temperature cooling energy uses, confirming the importance of adopting seasonal indicators customized on the actual operating conditions of chillers

Thermodynamic-based method for supporting design and operation of thermal grids in presence of distributed energy producers

District heating networks are well-established technologies to efficiently cover the thermal demand of buildings. Recent research has been devoting large efforts to improve the design and management of these systems for integrating low-temperature heat coming from distributed sources such as industrial processes and renewable energy plants. Passing from a centralized to a decentralized approach in the heat supply, it is important to develop indicators that allow an assessment of the rational use of the available heat sources in supplying heating networks, and a quantification of the effect of inefficiencies on the unit cost of heat. To answer these questions, Exergy Cost Theory is here proposed. Thanks to the unit exergetic cost of heat, energy managers can (i) quantify the effects of thermodynamic inefficiencies occurring in the production and distribution on the final cost of heat, (ii) compare alternative systems for heat production, and (iii) monitor the performance of buildings’ substation over time. To show the capabilities of the method, some operating scenarios are compared for a cluster of five buildings in the tertiary sector interconnected by a thermal grid, where heat is produced by a cogeneration unit, an industrial process, and distributed heat pumps. Results suggest that moving from the centralized production of heat based on fossil fuels to a decentralized production with air-to-water heat pumps, the unit cost of heat can be decreased by almost 30% thanks to the improvement of thermodynamic efficiency. In addition, the analysis reveals a great sensitivity of unit exergetic cost to the maintenance in substations. The developed tool can provide thermodynamic-sound support for the design, operation, and monitoring of innovative district heating networks

Assessing the Energy-Saving Potential of a Dish-Stirling Concentrator Integrated into Energy Plants in the Tertiary Sector

Energy consumed for air conditioning in residential and tertiary sectors accounts for a large share of global use. To reduce the environmental impacts burdening the covering of such demands, the adoption of renewable energy technologies is increasing. In this regard, this paper evaluates the energy and environmental benefits achievable by integrating a dish-Stirling concentrator into energy systems used for meeting the air conditioning demand of an office building. Two typical reference energy plants are assumed: (i) a natural gas boiler for heating purposes and air-cooled chillers for the cooling periods, and (ii) a r reversible heat pump for both heating and cooling. For both systems, a dish-Stirling concentrator is assumed to operate first in electric-mode and then in a cogenerative-mode. Detailed models are adopted for plant components and implemented in the TRNSYS environment. Results show that when the concentrator is operating in electric-mode the electricity purchased from the grid decreases by about 72% for the first plant, and 65% for the second plant. Similar reductions are obtained for CO₂ emissions. Even better performance may be achieved in the case of the cogenerative-mode. In the first plant, the decrease in natural gas consumption is about 85%. In the second plant, 66.7% is the percentage increase in avoided electricity purchase. The integration of the dish-Stirling system allows promising energy-saving and reduction in CO₂ emissions. However, both a reduction in capital cost and financial support are needed to encourage the diffusion of this technology

Thermoeconomic Diagnosis Of Air Conditioning Systems: Experimental Assessment Of Performance And New Developments For Improved Reliability

In the last two decades, great progress has been made in improving the efficiency of air-conditioning equipment. In addition to improved performance of new equipment, there has been an increasing interest in technologies that can maintain performance over time. This has led to research and development of Fault Detection and Diagnosis (FDD) techniques for air conditioning systems, that can support building owners in scheduling cost-effective maintenance and repairs. Among FDD techniques, thermoeconomic diagnosis is a novel method for the identification of faults occurring in air conditioning systems. A very limited number of papers have focused on this topic, and the methodology is still at a very early stage of development. Thermoeconomic diagnosis is an exergy-based method to quantify the additional energy consumption (or the EER penalty) associated with individual or combinations of faults. It has been initially tested for very simple vapor compression systems through simulation, but has never been evaluated using experimental data. This work aims to assess the performance of thermoeconomic diagnosis using experimental data obtained from a five-ton variable-speed packaged rooftop air conditioning unit (RTU). The RTU was tested in psychrometric chambers under a wide range of operating conditions and fault levels. Three faults that are commonly found in rooftop systems were investigated: (i) evaporator fouling, (ii) condenser fouling and (iii) refrigerant undercharge. The experimental results were used as inputs in an equipment model, to characterize the exergy behavior of each component in presence of faults and apply the approach of Symbolic Exergoeconomics. Experimental results show the technique had difficulty in detecting some faults and its performance is quite sensitive to operating conditions. Based on these results, improvements to the FDD methodology based on empirical models of plant components are proposed. These improvements act to isolate the effects of operating conditions from the thermoeconomic effects of different faults, improving overall performance

Integrated thermodynamic and control modeling of an air - to - water heat pump for estimating energy - saving potential and flexibility in the building sector

Reversible heat pumps are increasingly adopted for meeting the demand for space heating and cooling in buildings. These technologies will play a key role not only in the decarbonization of space air conditioning but also in the development of 100% renewable energy systems. However, to assess the achievable benefits through the adoption of these technologies in novel applications, reliable models are needed, capable of simulating both their steady-state operation and dynamic response at different conditions in terms of heating loads, outdoor temperatures, and so on. The operation of heat pumps is often investigated by highly simplified models, using performance data drawn from catalogs and paying scarce attention to the critical influence of controllers. In this respect, this paper proposed an integrated thermodynamic and control modeling for a reversible air-to-water heat pump. The study considered a heat pump alternatively equipped with variable-speed compressors and constant-speed compressors with sequential control. The developed modeling was then used to investigate the operation of an air-to-water heat pump serving an office building in Italy. Results show that the model provided insights into the transient operation of variable-speed heat pumps (e.g., the settling time). Regarding constant-speed heat pumps, the model provided hints of interest to the control engineer to prevent, in the examined case study, the risk of quick compressors cycling on low-load heating days or when low-temperature heating devices are supplied. Finally, using a control strategy based on a heating curve for the variable-speed heat pump, results show the potential for a sensible increase in the average coefficient of performance, from 17% up to 50%

Advanced modeling and energy-saving-oriented assessment of control strategies for air-cooled chillers in space cooling applications

Chillers are reference technologies to meet the demand for space cooling in the tertiary and commercial sectors. Meantime, being power-to-cold technologies, they could increase the flexibility of these buildings in those contexts of a high share of electricity from renewable energy sources through new control strategies. To reliably assess the achievable energy savings in these novel applications, models capable of simulating not only the steady-state operation but also the dynamic response are required. However, the operation of these systems is usually evaluated through highly simplified models, also omitting controls. To fill this gap, this paper proposes an integrated thermodynamic and control modeling for an air-cooled chiller, accounting for usual and innovative control strategies. To show the capabilities of the model, an air-cooled chiller serving an office in the Mediterranean area is assumed. Both a variable-speed chiller and a constant-speed chiller with sequential control for compressors are simulated. Results show that for a variable-speed chiller, the set point for the supplied cold water is met, and the thermal inertia of the hydronic loop affects the reaching of the steady-state operation. In the case of a constant-speed chiller with sequential control, the number of “ON-OFF” cycles for each compressor is monitored and the minimum inertia of the hydronic loop for the safe operation of compressors is found. The analysis reveals that a variable temperature setpoint for the supplied water allows for a percentage increase in the energy performance between 10.8% and 60.3%. The proposed model enables the analysis of innovative controls aimed at improving energy savings and increasing building flexibility

Energy-saving potential of ground source multiple chillers in simple and hybrid configurations for Mediterranean climates

Air conditioning accounts for a large share of energy usage in residential and tertiary sectors. Renewable energy technologies offer promising solutions to reduce the environmental impacts of meeting buildings’ energy loads. The possibility of using the soil as a thermal reservoir for heating and cooling systems has gained growing attention in the last decade due to its high potential for energy saving. In this paper, the benefits achievable using ground source chillers for air conditioning in an office building located in Southern Italy are discussed. A multiple chillers system coupled with a borehole heat exchanger is investigated and compared to conventional air-cooled and water-cooled systems. The analysis relies on detailed modeling of the main plant components and exploits a novel approach to calculating the thermal resistance of the borehole. Results show that the ground coupled multiple chillers system achieves a 6.516 average energy efficiency ratio, which is 53.2% higher than the reference air-cooled system and 6.5% higher than the conventional water-cooled system. In addition, a hybrid scheme that integrates the borehole heat exchanger with a cooling tower achieves a 19.5% reduction in make-up water consumption. A sensitivity analysis demonstrates that increasing the borehole depth could lead to a significant variation in the system performance, with different trends for simple and hybrid configurations. The proposed study puts forth a reference for the design and operation of this technology for covering the space-cooling demand of buildings in Mediterranean climates

INNOVATIVE APPLICATIONS OF EXERGY ANALYSIS AND THERMOECONOMICS IN CHEMICAL, THERMAL AND COOLING ENERGY CONVERSION SYSTEMS

Since 70s, the world has been becoming more and more concerned about energy and environmental issues. The need of meeting the current energy demand by guaranteeing the ability of future generation to satisfy theirs have been pushing research not only to exploit alternative energy sources such as renewable energies, but also to improve the efficiency of energy conversion systems. To this regard, developing systems that use efficiently energy is of paramount importance especially in those countries which rely on non-renewable energy sources such as oil, natural gas, and coal. In fact, the reduction of energy consumption will lead not only to the saving of unrestorable and limited energy resources but also to some environmental benefits, such as the reduction of carbon dioxide emissions. To this am, a lot of methods have been developed across scientific research. Among them, Exergy Analysis and Thermoeconomics are well-recognized for supporting the analysis and design of any energy conversion system. This thesis deals with innovative applications of Exergy Analysis and Thermoeconomics in chemical, thermal and cooling energy conversion systems. It aimed at demonstrating the capabilities of both methods to provide insights into design alternatives and operation strategies of energy conversion systems. Exergy Analysis of Reverse ElectroDialsysis process is carried out. This innovative energy system converts salinity gradient into electricity, by interposing selective membranes between two solutions at different concentrations. The analysis aims at providing insights into the effects on the exergy performance of the current membrane properties and of some design and operating parameters. Results will be useful for the future development of this system. A further exergy analysis is focused on the integration of Reverse Electrodialysis process with Multi-effect Distillation Unit. This innovative system allows for the conversion of low-grade heat into electricity. Efforts are still needed to improve the energy performance of this system and to this aim, exergy analysis allows for evaluating the effect of some design and operating parameters. Thermoeconomic Cost Accounting is applied to Multi-Effect Desalination (MED) process, of which energy consumption highly affect the operating costs. In order to gain insights into the cost formation process of the produced freshwater, a thermoeconomic analysis of this system is carried out by adopting a high disaggregation level. The analysis allows for understanding at which extent the irreversibility occurring at each subprocess affects the cost of freshwater. Then, the same system is supposed to be operated in a cogenerative asset realized by coupling it with a steam power plant. In this case, Thermoeconomics provides a method for apportioning cost on electricity and freshwater produced. Another innovative method investigated in this thesis is the Thermoeconomic Diagnosis of energy systems. This Fault Detection and Diagnosis Technique has been extensively applied to thermal power plants, but only recently it has been extended to Heating, Ventilation and Air Conditioning Systems (HVAC). With this respect, most of results achieved so far have been based on a set of virtual-experiments thus not allowing to account for real operation of these system. For the first time, the method is tested using experimental data obtained from a packaged rooftop air conditioning unit. Last but not least, the applications of exergy-based methods to environmental analyses is considered. To this regard, an innovative approach based on integration of Thermoeconomics and Life Cycle Assessment (LCA) is here proposed. The procedure combines the capabilities of these two techniques to account simultaneously for aspects related to thermodynamics of energy conversion processes and to the overall impacts along the plant life cycle, i.e. from raw material extraction to the disposal of facilities. The capabilities of this approach are illustrated by applying it to a water-cooled vapor compression chiller

Getting insights into the behavior of variable speed direct expansion air conditioning systems under faulty operating conditions

Direct expansion air conditioning systems, such as rooftop units, are widely adopted in small and medium scale commercial buildings. In order to increase the energy performance of these systems during part-load operation, variable-speed compressors and fans have been adopted in the last two decades. However, profitable energy saving could be achieved not only by optimizing the design and the control of these systems, but also by scheduling a proper maintenance strategy. In fact, if not properly maintained, no benefits would be achieved even when more sophisticated systems are adopted. In order to support plant owners in scheduling cost-effective maintenance program, Fault Detection and Diagnosis techniques could represent promising tools for monitoring the performance over time. However, only fixed-speed air-conditioning systems have been considered during these years. This work aims at providing insights into the effects of common faults such as condenser fouling, evaporator fouling and charge faults in variable-speed direct expansion systems. To this aim, the analysis was based on an intensive experimental campaign carried out on a 17.5 kW rooftop unit installed at Herrick Laboratories, Purdue University (USA). Results allowed for describing the response of the investigated rooftop unit in terms of pressures, temperature and power consumption and so forth when considering full-load and part load operation for faults-free and faulty operating condition. These results will orient the development of innovative Fault Detection and Diagnostic techniques for these systems

Assessing the Robustness of Thermoeconomic Diagnosis of Fouled Evaporators: Sensitivity Analysis of the Exergetic Performance of Direct Expansion Coils

Thermoeconomic diagnosis of refrigeration systems is a pioneering approach to the diagnosis of malfunctions, which has been recently proven to achieve good performances for the detection of specific faults. Being an exergy-based diagnostic technique, its performance is influenced by the trends of exergy functions in the “design” and “abnormal” conditions. In this paper the sensitivity of performance of thermoeconomic diagnosis in detecting a fouled direct expansion coil and quantifying the additional consumption it induces is investigated; this fault is critical due to the simultaneous air cooling and dehumidification occurring in the coil, that induce variations in both the chemical and thermal fractions of air exergy. The examined parameters are the temperature and humidity of inlet air, the humidity of reference state and the sensible/latent heat ratio (varied by considering different coil depths). The exergy analysis reveals that due to the more intense dehumidification occurring in presence of fouling, the exergy efficiency of the evaporator coil eventually increases. Once the diagnostic technique is based only on the thermal fraction of air exergy, the results suggest that the performance of the technique increases when inlet air has a lower absolute humidity, as evident from the “optimal performance” regions identified on a psychrometric chart