Advanced Refrigerating Plants Based on Transcritical Cycles Working with Carbon Dioxide for Commercial Refrigeration

Results of calculations on the economic potential for alternative (low input, sustainable) farming systems in a small grain-row crop region of the Northern Plains are reported. Two sets of alternative farming systems, in which no chemical fertilizers or herbicides are used, are compared with various conventional and reduced till systems. In Farming Systems Study I (FSS1), an alternative rotation consisting of oats, alfalfa, soybeans, and corn is compared with conventional and ridge till rotation systems composed of corn, soybeans, and spring wheat. In Farming Systems Study II (FSS2), three systems with an emphasis on small grains are compared. An alternative system rotation consisting of oats, sweet clover, soybeans, and spring wheat is compared with conventional and minimum till rotation systems comprised of soybeans, spring wheat, and barley. Results of baseline economic analyses show that alternative farming systems can be competitive with more conventional systems in at least some situations. The alternative systems entail markedly lower direct costs, and the alternative system in FSS2 has approximately the same net returns as the comparable conventional and minimum till systems. The FSS1 alternative system has positive but somewhat lower net returns than the comparable conventional and ridge till systems. Sensitivity analyses were conducted with alternative system crop yields, chemical fertilizer and herbicide prices, and varying assumptions about future Federal farm program support levels and acreage set aside requirements. The yield sensitivity analyses show that one alternative farming system requires yields about 5–10 percent above those of the comparable conventional system to produce the same net returns. However, the other alternative system is competitive with a conventional system even with yields 5 percent lower. Analyses varying chemical fertilizer and herbicide prices reveal that the alternative farming system in FSS1 becomes competitive with more conventional systems when fertilizer and herbicide prices rise by 50 percent. The alternative farming system in FSS2 is already competitive at current fertilizer and herbicide prices. In some cases, sensitivity analyses with Federal farm program provisions indicate that reductions in farm program benefits increase the economic competitiveness of alternative farming systems. However, important exceptions occur. Results indicate that not only the level of future farm program benefits, but also the form of program provisions and compliance requirements, will affect the relative competitiveness of alternative farming systems.

The manufacturers of refrigeration equipment are facing challenges related to the legislative requirements forcing them to implement less conventional refrigerants with lower Global Warming Potential (GWP) in their new products. Natural working fluids like Ammonia, Carbon Dioxide and Propane have demonstrated to be energy efficient and environmentally benign alternatives. Ammonia refrigeration systems have been successfully in the market for more than 140 years. Especially at high ambient temperature conditions, these units can outperform conventional HFC systems. The cost, availability and detection of the fluid are no issue on a global base. Hydrocarbon based AC split units, applying propane, are in focus and large-scale production lines are under preparation. The fluid- and thermosphysical properties of CO2 are quite different from most other working fluids. Therefore, the refrigeration system design has to be carefully adapted to the properties of CO2, thereby maximising the energy efficiency and minimising the total cost of ownership. The article describes the challenges related to conventional refrigerants and examples of the latest system developments applying natural working fluids in industrial-, commercial and marine refrigeration will be described in the work.

Perspectives for natural working fluids in China

We compared the agronomic, economic, and ecological performance of alternative (organic), conventional, and reduced-till farming systems over a 7-year period. We evaluated the sustainability of the various systems regarding several concerns, including soil erosion, pollution potential, whole-farm productivity, energy use, environmental stress, economic performance, and farm size. The alternative systems relied primarily on forage legumes (alfalfa or clover) as substitutes for the pesticides and commercial fertilizers used in the other systems.Two studies were established in northeastern South Dakota in 1985. Study I emphasized row crops, Study II small grains. The alternative system in Study I, which included alfalfa hay in the rotation, was the most productive, both agronomically and economically. In Study II, the alternative system included a green manure crop (clover) in the 4-year rotation and had the lowest agronomic production; however, its economic performance was similar to the conventional system's. Year-to-year variability in production was lowest in the alternative systems. The alternative systems in both studies were the most energy-efficient, and the reduced-till systems the least. Judged by the distribution of nitrate-N in the soil profile, the potential for groundwater pollution was higher in the conventional and reduced-till systems in Study I than in the alternative system.The alternative systems in both studies depended less on government payments for their profitability. Results in Study I also showed that more widespread adoption of alternative systems would tend to halt or slow the trend of ever-increasing farm size. These studies suggest that alternative systems are more sustainable in this agro-climatic area.

Review of vapour compression heat pumps for high temperature heating using natural working fluids

Dates are subjected to postharvest losses in quality and quantity caused by water loss, fermentation, insect infestation, and microbial spoilage during storage. Cold storage is the main element in the postharvest quality management used for fruit preservation. Although cold storage is used for dates, precision control of the relative humidity (RH) using ultrasonic applications is not used thus far, or it is applied to other fruits on a small scale. Therefore, we designed and constructed an ultrasonic humidifier (DUH) for RH control in the cold storage room (CSR) of dates. The optimum air velocity of 3 m s−1 at the outlets of the DUH ducts produced a mist amount of 6.8 kg h−1 with an average droplet diameter of 4.26 ± 1.43 µm at the applied voltage of 48 V and frequency of 2600 kHz of the transducers. The experimental validation was carried out by comparing a CSR controlled with the DUH with two conventional CSRs. The three tested CSRs were similar in dimensions, cooling system, and amount of stored dates. The time required for cooling 800 kg of dates in the controlled CSR from 25 °C to the target temperature of 5 °C was approximately 48 h. The DUH precisely controlled the RH at the maximum RH set point of 80% in the tested CSR at 5 °C. The controlled RH at 80% has a positive impact on the physicochemical characteristics of the stored dates. It significantly reduced the weight loss of the fruits and preserved fruit mass, moisture content, water activity, firmness, and color parameters. However, no significant effect was observed on fruit dimensions, sphericity, and aspect ratio. The microbial loads of mesophilic aerobic bacteria, molds, and yeasts fell within the acceptable limits in all tested CSRs. Both stored date fruits and artificially infested dates showed no signs of insect activity in the controlled CSR at the temperature of 5 °C and RH of 80%. The DUH proved to be a promising technology for postharvest quality management for dates during cold storage.

Cold storage is deemed one of the main elements in food safety management to maintain food quality. The temperature, relative humidity (RH), and air quality in cold storage rooms (CSRs) should be carefully controlled to ensure food quality and safety during cold storage. In addition, the components of CSR are exposed to risks caused by the electric current, high temperature surrounding the compressor of the condensing unit, snow and ice accumulation on the evaporator coils, and refrigerant gas leakage. These parameters affect the stored product quality, and the real-time sending of warnings is very important for early preemptive actionability against the risks that may cause damage to the components of the cold storage rooms. The IoT-based control (IoT-BC) with multipurpose sensors in food technologies presents solutions for postharvest quality management of fruits during cold storage. Therefore, this study aimed to design and evaluate a IoT-BC system to remotely control, risk alert, and monitor the microclimate parameters, i.e., RH, temperature, CO2, C2H4, and light and some operating parameters, i.e., the temperature of the refrigeration compressor, the electrical current, and the energy consumption for a modified CSR (MCSR). In addition, the impacts of the designed IoT-BC system on date fruit quality during cold storage were investigated compared with a traditional CSR (TCSR) as a case study. The results showed that the designed IoT-BC system precisely controlled the MCSR, provided reliable data about the interior microclimate atmosphere, applied electrical current and energy consumption of the MCSR, and sent the necessary alerts in case of an emergency based on real-time data analytics. There was no significant effect of the storage time on the most important quality attributes for stored date fruit in the MCSR compared with the TCSR. As a result, the MCSR maintained high-quality attributes of date fruits during cold storage. Based on the positive impact of the designed IoT-BC system on the MCSR and stored fruit quality, this modification seems quite suitable for remotely managing cold storage facilities.

An alternative outdoor production system for the microalgae Chaetoceros muelleri and Dunaliella sp. during winter and spring in Northwest Mexico

For a sustainable future in energy, the use of natural fluids in heat pump systems can provide an efficient solution to combat the ozone depletion and the global warming effects of synthetic working fluids. These natural fluids, though environmentally friendly, must be able to operate at high temperature in heat pumps in an efficient and cost effective way to be viable for the industry heat demand. High temperature heat pumps with heat source and heat sink temperatures ranging from 40 oC to 200 oC have unique challenges with natural working fluids. This paper evaluates the performance and use of natural working fluids for high temperature heat pumps. The analysis is based on simple thermodynamic cycles. A simulation tool coupled with a thermodynamic properties database is used to evaluate the operating limitations of the natural fluids. Natural fluids such as ammonia, hydrocarbon and hydrocarbon mixtures are considered. The hydrocarbon mixtures, benefitting from both adjusted thermodynamic properties and a higher evaporating temperature due to better fit to heat source temperature, shows greatest potential for the development of high temperature heat pumps. The mixtures R290+R600 and R600+R601 were able to expand the working limits of their pure fluids while improving COP by up to 13.5 %.

Environmental problems such as ozone layer depletion and global warming are widely known as global issues. The Montreal Protocol totally prohibits use of HCFC from 2020 and Kigali revision of the protocol calls for gradual reduction of use of HFC by 85% towards 2036. In the industrial refrigeration, HCFC-22 refrigerant has been used for many years and HFC refrigerants are widely used as alternatives, however, conversion to refrigerants with less environmental impact is urgently required. Mayekawa developed and introduced a highly efficient refrigeration system called ‘NewTon’, applying the natural refrigerants ammonia (NH3) and carbon dioxide (CO2) as the primary and secondary refrigerants. The refrigeration system demonstrates a high energy saving compared to systems with traditional working fluids and in addition its direct environmental impact can be neglected since only natural working fluids are applied. These kind of units are widely used in freezing- and cold storage applications. In this work, the specific features of the ‘NewTon’ unit are described and energy consumptions are compared with historical demands of the systems, which have been replaced.

Space Design for Thermal Comfort and Energy Efficiency in Summer

Natural working fluids for solar-boosted heat pumps

Indoor thermal comfort is essential for occupants’ well-being, productivity, and efficiency. Global climate change is leading to extremely high temperatures and more intense solar radiation, especially in hot, humid areas. Passive cooling is considered to be one of the environmental design strategies by which to create indoor thermal comfort conditions and minimize buildings’ energy consumption. However, little evidence has been found regarding the effect of passive cooling on the thermal comfort of historical buildings in hot–dry or hot–humid areas. Therefore, we explored the passive cooling features (north-south orientation, natural ventilation, window shading, and light color painted walls) applied in historic residential buildings in Zanzibar and evaluated the residents’ thermal responses and comfort perception based on questionnaires and field surveys. The results showed that the average predicted mean votes (PMVs) were 1.23 and 0.85 for the two historical case study buildings; the average predicted percentages of dissatisfaction (PPD) were 37.35% and 20.56%, respectively. These results indicate that the thermal conditions were not within the acceptable range of ASHRAE Standard 55. Further techniques, such as the use of lime plaster, wash lime, and appropriate organization, are suggested for the improvement of indoor thermal comfort in historical buildings in Zanzibar. This study provides guidelines to assist architects in designing energy-efficient residential buildings, taking into account cultural heritage and thermal comfort in buildings.

Overview and outlook of research and innovation in energy systems with carbon dioxide as the working fluid

A heat pump water heater system using carbon dioxide refrigerant can supply high temperature water efficiently. Carbon dioxide is the natural working fluid without inflammability, toxicity and environmental impact. Otherwise carbon dioxide has high operating pressure and high density. We chose a swing compressor as the solution for this system. Practically, reduction of the operating sound is important for the system to operate in the nighttime. We developed a new compact heat exchanger and a new fan for suitable operation.