Chill Units Research Articles

Efficiency improvement of the air-cooled packaged water chiller unit with three-phase alternating current control technology

A three-phase alternating current control technology (TPACCT) was proposed and applied to the compressor of an air cooled packaged water chiller unit (ACH) to maintain the stable operation of the air-conditioning system and reduce energy consumption. The proposed TPACCT mainly uses a Single-Chip microcomputer to perform the calculations of the self-developed program, and uses a silicon controlled rectifier (SCR) component to trigger the voltage phase angle of ACH. Due to the drop of the controlled voltage, the current value is reduced, and the corresponding ACH active power also drops. This study attempts to reach the dynamic balance of voltage and current of the compressor in the air-conditioning system under heavy-load operating conditions to obtain the best control parameters. This study also conducted a long-term day-to-day experiment of the compressor, mainly analyzing the cumulative energy consumption of ACH when operating in a single zone, and comparing the energy-saving effect of the proposed TPACCT with the case operating under mains electricity. Results show that the cumulative energy consumption is about 5% lower than that of mains electricity mode. Different energy-saving strategies are provided for air-conditioning systems that need to be maintained under heavy-duty operation for a long time.

Small RNA Differential Expression Analysis Reveals miRNAs Involved in Dormancy Progression in Sweet Cherry Floral Buds.

In sweet cherry (Prunus avium), as in other temperate woody perennials, bud dormancy allows for survival in adverse environmental conditions during winter. During this process, environmental signals such as short days and/or low temperatures trigger internal signals that enable buds to become tolerant to the cold. The process involves tracking chilling units up to chilling the requirement fulfillment to resume growth, a transition involving transcriptional regulation, metabolic signaling, and epigenetic-related regulatory events. Massive sequencing of small RNAs was performed to identify miRNAs involved in sweet cherry dormancy by comparing their expression in field (regular seasonal) and controlled non-stop (continuous) chilling conditions. miRNAs highlighted by sequencing were validated using specific stem-loop PCR quantification, confirming expression patterns for known miRNAs such as miR156e, miR166c, miR172d, miR391, miR482c, and miR535b, as well as for newly proposed miRNAs. In silico prediction of the target genes was used to construct miRNA/target gene nodes. In particular, the involvement of the sweet cherry version for the miR156/SQUAMOSA PROMOTER-BINDING-LIKE PROTEIN genes whose expression was opposite in the two conditions suggests their involvement on dormancy regulation in sweet cherry. miRNA levels indicate that the regulation of stress-related genes and hormone synthesis modulates the expression of calcium metabolism and cell development-associated genes. Understanding the regulatory networks involved in sweet cherry dormancy, particularly in the context of miRNA involvement, represents the first step in the development of new agricultural strategies that may help overcome the increasing challenges presented by global climate change.

Experimental investigation on energy saving potential for thermally activated buildings integrated with the active cooling system

ABSTRACT A thermally activated building system (TABS) is the most promising technology for reducing heat gain, cooling demand, and improved indoor comfort inside the built environment. This study investigates the energy consumption and thermal environment performance of the cooling tower-based thermally activated building system (passive system) integrated with a chiller unit (active cooling system). Energy consumption and indoor environment parameters, such as heat flux, indoor air, wall, floor, and the operative temperature, were measured in two computer laboratories of the same size and orientation operated with a chiller unit and chiller-integrated passive system. This strategy involved pre-cooling the building thermal mass during unoccupied hours via TABS and continuously using the system while maintaining zone temperatures at the comfort region during the occupied period. The results show that chiller-integrated TABS has a maximum heat gain of 10 W/m2 and maintains a mean radiant temperature from 24°C to 26°C for 80% of the interval. Furthermore, due to the pre-cooling effects of TABS, chiller-integrated TABS has a peak monthly energy savings of 6% and a CO2 emission reduction of 8% compared to an active cooling system.

The Optimal Operation and Dispatch of Commerce Air-Conditioning System by Considering Demand Response Strategies

The purpose of this paper is to discuss an optimal operation and schedule of commerce air-conditioning system by considering the demand response in order to obtain the maximal benefit; this paper first collects the operating data of the chiller units in commercial users, calculates the cooling load of each unit, and derives the relationship between the cooling loads and power consumption of each unit. The weather information, such as temperature and humidity of inside/outside, are collected in the EXECL database, and the cooling load of the mall’s space is simulated by using the Least Square Support Vector Machine (LSSVM). Under the selected plan of power reduction, the requirement of space cooling loads, and the various operation constraints, the dispatch model of the commerce air-conditioning system with demand response strategies is formulated to minimize the total cost. A Modify Particle Swarm Optimization with Time-Varying Acceleration Coefficients (MPSO-TVAC) is proposed to solve the daily economic dispatch of the air-conditioning system. In the MPSO-TVAC procedure, the dynamic control parameters are embedded in the particle swarm of the PSO-TVAC in order to improve the behavior patterns of each particle swarm and increase its search efficiency in high dimensions. Different modifications in moving patterns of MPSO-TVAC are proposed to search the feasible space more effectively. By using MPSO-TVAC, it provides an optimal mechanism for variables regulated to increase the efficiency of the performing search and look for the probability of an optimal solution. Simulation results also provide an efficient method for commercial users to reduce their electricity bills and raise the ability of the market’s competition.

Case representation and retrieval for complex product design based on case-based reasoning

Reusing design knowledge of products is a useful way to solve the efficiency issue of complex product design. The design knowledge is tacit, empirical, and unstructured and there exists insufficient case matching and inefficient design reuse in complex products design process. Aiming at these problems, this paper presents an improved case-based reasoning methodology combining ontology with two-stage retrieval. Firstly, a knowledge domain ontology model of complex product design is constructed, and the technology of ontology-based data access is introduced to automatically generate a case knowledge base with semantic information. Then, a new two-stage case retrieval method integrated semantic query with similarity calculation is proposed. The case subset is selected by query statements. It has the characteristic of isomorphism with design problem. The retrieval mechanism is applied to compress the traversal space, reduce the redundancy of semantic similarity calculation, improve the retrieval efficiency, and fulfill the target of case reuse. Finally, a variant design of the chiller unit as an example is executed to illustrate the use of the proposed method, and experiments are organized to evaluate its performance. The result shows that the proposed approach has an average precision of 92% and high stability, outperforming existing methods.

Genetic Pool of the Cultivated Pear Tree (Pyrus spp.) in the Canary Islands (Spain), Studied Using SSR Molecular Markers

The Canary Islands have an enormous richness of crops and varieties, many of them traditional or local, selected for decades by farmers based on the most desirable characteristics. Pear trees were introduced to the Canary Islands presumably in the first years after their Conquest in the 15th century, reaching a high degree of diversification. In this study, to determine the genetic identity of the genus Pyrus in the Canary Islands for conservation purposes, 266 pear accessions from the islands of Tenerife, La Palma and Gran Canaria were characterized with 18 SSRs, in addition to 190 genotypes from Galicia, Asturias, wild and commercial varieties as references to detect possible synonyms, genetic relationships and the possible genetic structure. We identified 310 unique genotypes, both diploid and putative triploid, 120 of them present only in the Canary Islands (39%, with 50% clonality). The population structure of the genotypes was analyzed by STRUCTURE 2.3.4 software (Pritchard Lab, Stanford University, Stanford, CA, USA). The dendrogram, by using the Jaccard coefficient and principal component analysis (PCoA), separated the analyzed genotypes into stable groups. One of these groups was formed only by Canarian varieties present at lower altitudes, showing adaptation to low chilling requirements with a significant positive correlation (0.432, p < 0.01). This first study of the pear germplasm in the Canary Islands reflects the importance of the group of local cultivars and their need for conservation given they are adapted to their peculiar climatic conditions and have a low number of chill units.

Apple mutant trees with low chilling requirements: Proximal, genetic and DNA methylation analyses

In Arteaga, Coahuila, Mexico, different apple mutants derived from the Golden Delicious cultivar have been identified. They are characterized by their low chilling requirements (350–650 Chilling units (CU)) for breaking dormancy, and high flower production. The aim of this study was to determine the bromatological, genetic, and DNA methylation differences among ten apple mutants, and the wild-type Golden Delicious cultivar. The bromatological analyses showed that there are slight differences between some apple mutants with respect to control (Golden Delicious); in most cases, mutants were similar to each other. On the other hand, the genetic diversity among apple genotypes accessed by ISSR markers showed 57.12% of polymorphism among the 11 apple genotypes. The methylation assay showed that the Verde mutant from the Huachichil location had the highest values of DNA methylation (87.49%), even higher than the control (Golden Delicious). Furthermore, in the San Antonio of Alazanas location, the Tunal and Vigas II mutants showed the highest values of DNA methylation (62.85 and 87.61, respectively), however, the chilling requirements between these two cultivars are very different (340 and 750 CU, respectively), so it was concluded that a higher chilling requirement, is not always caused by a higher percentage of methylation. The study of these mutants may allow development of apple tree cultivars with desirable characteristics under warm winter conditions.

Case study of office noise and vibration annoyance due to building water pumps for HVAC equipment

The background noise and vibration in an office workplace area was observed to be excessive. Next to one of the executive offices, as well as an open office space, is a mechanical room that provides heating and cooling to part of the 3-story college campus building. Inside this mechanical room are two hot and two cold water pumps which are part of the HVAC system of the building, as well as two boilers and a pump to a nearby chiller unit. Measurements have determined that these pumps are the main source of noise annoyance. The first task was to determine if the sounds meet the criteria stated in ASHRAE and ANSI standards. The background sound was measured during several occurrences as A-weighted, C-weighted, octave bands, and time recordings to processes narrowband spectrum. RC Mark II and NC levels were calculated from the data, and it was determined that the noise levels are often significantly above the criteria for office spaces. Narrowband and sound recordings indicate tonal acoustic signals generated by the pumps that lead to a higher level of annoyance.

Effects of chill unit accumulation and temperature on woody plant deacclimation kinetics.

Woody perennials in temperate climates develop cold hardiness in the fall (acclimation) and lose cold hardiness in the spring (deacclimation) to survive freezing winter temperatures. Two main factors known to regulate deacclimation responses are dormancy status and temperature. However, the progression of deacclimation responses throughout the dormant period and across a range of temperatures is not well described. More detailed descriptions of dormancy status and temperature, as factors regulating deacclimation, are necessary to understand the timing and magnitude of freeze injury risks for woody perennials in temperate climates. In this study, we modeled deacclimation responses in cold‐climate interspecific hybrid grapevine cultivars throughout the dormant period by integrating chill accumulation and temperature through the concept of deacclimation potential. We evaluated deacclimation and budbreak under multiple temperature treatments and chill unit accumulation levels using differential thermal analysis (DTA) and bud forcing assays. Deacclimation responses increased continuously following logistic trends for both increasing chill unit accumulation and increasing temperature. There are optimal temperatures where deacclimation rates increased but changes in deacclimation rates diminished below and above these temperatures. The cumulative chill unit range where deacclimation potential increased overlapped with the transition from endo‐ to ecodormancy. Therefore, deacclimation potential could provide a quantitative method for describing dormancy transitions that do not rely on the visual evaluation of budbreak. This information provides a more detailed understanding of when and how deacclimation contributes to increased risks by freezing injury. In addition, our descriptions could inform improvements to models predicting cold hardiness, dormancy transitions, and spring phenology.

Development and Experimental Study of Smart Solar Assisted Yogurt Processing Unit for Decentralized Dairy Value Chain

Yogurt production at the farm level is important for adding value to milk. In this study, a solar-assisted yogurt processing unit capable of performing the three processes of heating, fermentation, and cooling in a single unit was developed. It consisted of a circular chamber surrounded by a coil for heating by a solar vacuum tube collector and a pillow plate for cooling by a solar PV-powered chiller unit. Experiments were performed using 50, 40 and 30 L of raw milk under a constant water circulation rate of 50 L per minute for heating followed by a cooling process under 36, 18 and 6 rpm of stirrer speeds. The heat absorption rates of the milk were 5.48–0.31, 4.75–0.16 and 4.14–0.24 kW, and the heat removal rates from water ranged from 6.28–0.49, 5.58–0.49 and 4.88–0.69 kW for 50, 40 and 30 L of milk volume, respectively. The overall heat transfer efficiency was above 80% during the heating process. A stirring speed of 18 rpm was found to be optimal in terms of cooling speed and consistency of the yogurt. The total energy consumed was calculated to be 6.732, 5.559 and 4.207 kWh for a 50, 40 and 30 L batch capacity, respectively. The study offers a sustainable energy solution for the decentralized processing of raw milk, particularly in remote areas of the developing countries where access to electricity is limited.

ANALISA KOEFISIEN UJUK KERJA MESIN PENDINGIN (CHILLER) UNIT 1 PADA POWER HOUSE

Each refrigerant has different characteristic properties which affect the refrigeration effect and the resulting coefficient of performance (COP). A refrigeration machine that works by cooling water is called a refrigeration machine chillers. Chiller is an air conditioner with no cooling system direct. In this indirect cooling system, the refrigeration engine does not instantly cools the air in every room. Refrigeration machine cools water demin first, then this cold demin water is used for cool the air in the room. Cold demin water as cooling medium to reduce the temperature of a wide room at power house (PH) PLTA Musi. The method used in working on this practical work report is:by making observations or observations in the field, conducting interviews (interview) with supervisors and practical work supervisors regarding theoretical data (specification data). In this study, the Cooling Performance Coefficient (COP) was analyzed On Power House (PH) PT PLN (PERSERO) UL PLTA Musi The results of this study get the conclusion, namely: The coefficient of performance (COP) on the machine chiller unit 1 in Power House PLTA Musi by 4.22 is smaller than specification coefficient. This indicates that the cooling system is working properly optimal.

Chilling requirement of four peach cultivars estimated by changes in flower bud weights

The adaptation of temperate fruit crops is a challenge being increased by the global warming. Chilling requirement is a key factor for adaptation. The objective of this study was to estimate the chilling requirement of peach cultivars BRS Bonão, Esmeralda, Granada and Eragil, using the Tabuenca test. Chilling accumulation was computed using four different chilling hour (≤ 7.2 ºC and ≤ 11 ºC) models; and chill units using the Low Chill model and the Taiwan model. The fresh bud weight and bud water contents were also evaluated. The Tabuenca test (based on differences in bud´s dry weight) showed a fairly good efficiency for estimating the end of dormancy in peach. However, under mild winter conditions, it is better to use fresh bud weights. Either one of three chilling accumulation computation models (temperature ≤ 7.2 °C, ≤ 11°C, or Taiwan model) is suitable to classify comparatively different cultivars, but none is accurate enough to conclude on the adaptation of a given cultivar to a specific site. Using hours of temperatures ≤ 11 ºC: ‘BRS Bonão’ needed around 180 hours for dormancy release; ‘Esmeralda’ around 250 hours; ‘Granada’ between 300 and 400 hours, and ‘Eragil’ more than 500 hours.

Entire Whitening of Apple Trees to Increase Chill Units in Regions of Warm Temperatures during the Fall-Winter Seasons

Different studies have shown that global warming and climate change have increased the planet’s temperature in different locations. For the apple-growing farmers, this may have a negative impact on the accumulations of chill units when the air temperature during the fall-winter season increases. When the entire trees are covered with a reflective material, the wood temperature may decrease. Therefore, the objective of this study was to evaluate the effect of whitening (with calcium hydroxide) the entire apple trees (Malus domestica Borkh) after defoliation, on the branches and trunks’ internal temperature (under the bark), the accumulation of chill units (CU), its effects on fruit yield and quality and the relation with the use of thidiazuron (TDZ) (inducer of budbreak). The study was conducted during the fall-winter seasons of 2019-2020 and 2020-2021. The results of this study showed that at the hours of the highest incidence of solar radiation, the internal temperature of the whitened trunks and leaves decreases up to 9°C and 6°C respectively. The accumulated CU during the time of the study, of the whitened branches were up to 81% higher than the ones recorded on the branches with no whitening; while the CU was lost at the hours of highest solar radiation (due to a high temperature) were up to 37.2% smaller. Entire tree whitening increased up to 26% of the yield per tree compared to the application of TDZ. No statistical difference in fruit quality was observed between whitened trees and those with no whitening but with the application of thidiazuron.

DESIGN, CONSTRUCTION AND TESTING OF A COLD STORE WITH WATER-COOLED CHILLER

Objective of this research was to design, construction and test of a cold store with chiller unit. Dimensions of the cold store were 5x4x3m. Heat load was calculated and capacity of cooling system was determined. Ambient temperature was set 2oC and relative humidity 90% for cold store testing. Ambient temperature, relative humidity and air velocity were measured for 3 different levels and 12 points for each level in the cold store. Total heat load and capacity of cooling system were calculated 5222 kcal/h. and 6.07 kW respectively. The descriptive statistics were calculated for the ambient temperature; mean, 2.82oC, standard deviation 0.02oC and CV(%) 0.56, and for the relative humidity; mean 88.01%, standard deviation 0.61 (%) and CV(%) 0.70 and for the air velocity mean 0.37m/s, standard deviation 0.22 m/s, CV 33.45 %. Even the air velocity CV was high, the ambient temperature and relative humidity variations were evaluated very good.

Technical challenges and opportunities for milk chilling unit based on vapor absorption refrigeration systems

Vapor absorption refrigeration systems are a heat driven technology and have been used for many years. This technology is used today in remote locations where electricity is not available. It has several applications like cold storage, milk chilling unit and district cooling. In this study problems associated with conventional VARS is being discussed. Beside this several other aspect like fluid and salt used for VARS is also discussed. The main focus is given on milk chilling unit along with the proposed solution. This study also includes design changes in VARS for milk chilling unit. The solution recommended for VARS is replacement of solution pump with bubble pump. A brief discussion on new proposed experimental setup has also being done to overcome the limitation of power supply in remote locations.

Efficiency Improvement of the Air-Cooled Packaged Water Chiller Unit with Three-Phase Alternating Current Control Technology

Efficiency Improvement of the Air-Cooled Packaged Water Chiller Unit with Three-Phase Alternating Current Control Technology

SUPERVISED TUNING OF A CHILLER WITH A COLD PHASE-CHANGE MATERIAL USING AN RSM-SMITH PREDICTOR

The proposed work is focused on the tuning of the latent-heat storage of a PCM with MWCNT encapsulation for a chiller system in the milk-pasteurization process using an RSM-based predictive Smith controller. The PCM was synthesized using sodium polyacrylate and MWCNT particles, encapsulated in spherical balls stored in the IBT (ice bank tank of the chiller unit). Experimental work is conducted on the heat-transfer characteristics of the chiller unit with servo-operated flow-control valves based on the central composite design of experiments. The system is cascaded using a PID controller with a Smith predictor to stabilize the latent temperature of milk cooling in the chiller system. The system is considered to be a first-order transformation with the rise and settling time. The plant model is obtained, using the response-surface method based on the transfer function to minimize the error derivatives of the chiller system. Results of the proposed method show a robust performance in keeping the PCM temperatures and bacterial-growth value stabilized, allowing a less drastic control compared to the cascade-model predictive control.

Machine learning imputation of missing Mesonet temperature observations

Uninterrupted and reliable weather data is a necessary foundation for agricultural decision making, required for models based on accumulated growing degree days (GDD), chill units, and evapotranspiration. When a weather station experiences a mechanical or communications failure, a replacement (imputed) value should be substituted for any missing data. This study introduces a machine learning, network-based approach to imputing missing 15-minute and daily maximum/minimum air temperature observations from 8.5 years of air temperature, relative humidity, wind, and solar radiation observations at 134 AgWeatherNet (AWN) stations in Washington State. A random forest imputation model trained on temperature and humidity observations from the full network predicted 15-minute, daily maximum, and daily minimum temperature values with mean absolute errors of 0.43 °C, 0.53 °C, and 0.70 °C, respectively. Sensitivity experiments determined that imputation skill was related a number of external factors including volume and type of training data, proximity of surrounding stations, and regional topography. In particular, nocturnal cold air flows in the upper Yakima Valley of south-central Washington caused temperature to be less correlated with surrounding stations in the overnight hours. In a separate experiment, the imputation model was used to predict base- 10 °C GDD on 2020 July 1 trained entirely on 15-minute station data from previous years. Even with the entire season of observations missing, the model predicted the GDD value within an average error 1.4% with 125 of 134 stations within 5% of observations. Since missing data can typically be resolved within a timeframe of a few days, the network-based imputation model is a sufficient substitute for short periods of missing observational weather data. Other potential applications of an imputation model are briefly discussed.

A survey of eight chilling models for apple trees in Southern Brazil under mild winters

ABSTRACT The main models used for estimating chill accumulation throughout the dormancy period of temperate fruit trees in Brazil were developed in temperate regions in the northern hemisphere. Thus, they exhibit low precision when they are used in regions with mild winters. However, there are several little-known models that are more precise. This study aimed at evaluating the precision of eight different estimation models of chill accumulation applied to five apple cultivars which were grafted on two distinct rootstocks in a region with mild winters. Based on the coefficient of variation, the Microsoft Excel® program was used for evaluating the precision of the following models: Utah, modified Utah, CH < 7.2°C, CH < 10°C, CH < 15°C, Low chill, Taiwan low chill and Daily positive Utah chill unit (PCU). The lowest precision was attributed to both models Utah and CH < 7.2°C (the most common model in Brazil). Models CH < 15°C, Taiwan low chill, Low chill and modified Utah were considered precise (coefficient of variation < 15% in annual chill accumulation and to evaluate requirement to overcome dormancy in cultivars). No important differences were observed in models precision between ‘M-26’ and ‘M-9’ rootstocks.

An inverse fault detection and diagnosis (IFDD) strategy for practical application on chiller product

Current research on chiller fault detection and diagnosis (FDD) is usually based on the multi-classification method for mixed multiple fault types. The establishment of a multi-classification FDD model requires obtaining extensive test data of normal operation and multiple common faults at different fault levels, so the cost-to-benefit ratio will not be accepted. In addition, because of the information interference between different types of fault data, FDD model is hard to avoid over-fitting or under-fitting, and there may be an intolerable high false alarm rate existing in product application. Therefore, it is difficult to promote FDD in actual chiller product applications. This paper proposes an inverse fault detection and diagnosis (IFDD) strategy, which is based on the characteristics of the target fault (the fault to be concerned) to establish a two-classification fault diagnosis model. Compared with the multi-classification method, the amount of fault test data required by the two-classification methods to realize fault diagnosis can be greatly reduced. With IFDD strategy, the detection and diagnosis are completed simultaneously, while fast calculation speed, high diagnosis accuracy rate and low false alarm rate are achieved. The core of the IFDD strategy is to concentrate resources to capture the characteristics of the target fault, and no longer classify other types of faults and normal operating conditions, so it can avoid the influence of information interference between multiple types of fault data in the fault diagnosis model. In order to verify the feasibility of this strategy, a 200 ton variable-speed screw chiller has been tested on the laboratory, and a database of normal operation, refrigerant leakage, refrigerant overcharge faults, and a new operating condition of insufficient cooling water flow is initially established. Based on the sensors configured by the chiller unit and using the exponentially weighted moving-average (EWMA) control chart for IFDD, the model's fault diagnosis accuracy for the target fault reaches 100%, and no false alarm appears after the transition period.