Heat-driven snow production applying ejector and natural refrigerant

An effect of climate change is fewer cold days and less natural snow at lower elevations. This has spurred the interest in temperature independent snow (TIS) production, i.e., refrigeration technologies that can produce snow at ambient temperatures above zero. Commercially available TIS systems require a higher power consumption than conventional systems, i.e., snow lances and guns. Thus, to ensure that future snow-making sites are sustainable, it is necessary to develop solutions with a minimal environmental footprint. One possibility is to utilize surplus heat from industrial processes or from a district heating network to drive snow-making systems. Examples of heat driven refrigeration technologies fit for this purpose are absorption cooling and ejector cooling, both applying natural refrigerants. This paper evaluates a solution for heat driven ejector-based snow making systems: a vacuum ice slurry system using water (R718) as refrigerant. The required amount of driving heat and its required minimum temperature level largely depend on the ejector characteristics. Thus, to enable a proper evaluation, detailed numerical simulations of the ejector design and its efficiency were performed, at different temperature levels of driving heat and ambient temperatures. Results were used as input to estimate the overall performance, in terms of specific energy consumption (per m3 produced snow), compared to other TIS systems. The ejector-based system can be driven by low-grade heat (80 °C) and is shown to be highly efficient if cold cooling water (≤ 10°C) is available.Heat-driven snow production applying ejector and natural refrigerantacceptedVersio

Performance analysis of high temperature heat pumps and thermal energy storages for a dairy

This paper analyses the performance of the integrated energy system of an existing dairy in Bergen, Norway. The investigated dairy has an innovative solution for the thermal process supply by using only heat pumps and thermal energy storage to cover all temperature levels of the existing heating and cooling demand. The aim of the study was to determine the energy consumption and system performance for one winter week and one summer week and compare these results against each other. To evaluate the performance, a comprehensive energy analysis was carried out based on the available process data. The results show for a comparatively energy-intensive week in February that the integrated energy system covers the existing demand and can compensate for demand peaks, with a waste heat recovery rate of over 95% for the process. The chillers and heat pumps achieved high COPs in the range of 4.2 to 5.9, while the overall system achieved a total COP of 4.1. A comparative week in June was then investigated and compared with the results of the operating week in February. Due to higher building cooling demands and lower building heating demands, the demand for dry cooling was significantly increased in the summer, whereas the need for electric heating and district heating was reduced. The achieved COPs in the range of 4.2 to 5.7 were similar in the summer week, meaning that the energy system functions well in different climatic conditions. Based on the results of this study, the performance of the system under different conditions was evaluated and the impact on power consumption and potential use for other climatic regions was discussed.Performance analysis of high temperature heat pumps and thermal energy storages for a dairyacceptedVersio

Heat-driven snow production

Global warming is causing increased temperatures and reduced snow cover, which threatens the possibility to exercise winter sports activities near populated areas in the future. Temperature Independent Snow (TIS) production can contribute to increase the snow reliability for winter sport. However, this method is very energy intensive and to reduce operational costs the use of heat instead of electricity as energy source is a potential solution. Absorption appears to be most promising among the possible heat driven refrigeration technologies. Heat supply temperatures can be as low as 85-90°C, which opens the possibility for using district heating. Calculations showed that a thermally driven refrigeration system for TIS production is more than twice as energy intensive compared to using electricity and will depend on low energy costs to be competitive. The review of potential heat sources shows that there is a potential for utilization of district heating and industrial waste heat. District heating is the most prevalent and about 40 % of the identified winter sport facilities are in municipalities where this is offered. However, low temperatures and lack of available heat are potential challenges. Industrial waste heat exists in large quantities at sufficient temperature levels but is less co-located with the winter sports facilities. Furthermore, there are important factors related to cost and technology, which can limit the potential for utilization.publishedVersio

Predicting the Extent of Root and Butt rot in Stems of Norway Spruce (Picea abies)

Commercially, Norway spruce (Picea abies (L.) Karst) is the most important tree species in Norway, representing 72% of the industrial timber volume sold in 2019. However, Norway spruce is particularly prone to infection of root and butt rot pathogens, degrading the value of the resource. Studies using National Forest Inventory Data (NFI) show that the nationwide rot frequency of Norway spruce is somewhere between 7.9-9.5%. Other studies have indicated that the presence of root and butt rots are in proportions of approximately 1 out of 5 Norway spruce trees. Root and butt rots cause substantial annual economic losses estimated at NOK 100 millions. The losses are related to degradation of timber resources, per instance, culled by the harvester operator. However, the extent of which the root and butt rots develops up the stem is not known by the harvester operator. Therefore, developing a practical prediction model for rot heights in Norway spruce, to guide the operator in decision making, was addressed in this thesis. The data sampling was carried out on three different occasions. In the first sampling, root and butt rot infected spruce trees were identified. Secondly, the trees were cut to examine the extent of rot in the stems. At last, tree-specific measurements were gathered. The prediction model could explain approximately 21% of the variance in the dataset. Individually, the independent variables diameter at root, proportion of rot and tree height, showed a positive relationship to the prediction of rot height, with increasing values increasing the prediction of rot height. In the evaluation of the prediction model using optimal bucking, a total utilization grade of 76% was discovered. On tree level, the utilization grade was 74% with a standard error of 18%.Gran (Picea abies (L.) Karst) er det kommersielt viktigste treslaget i Norge, med en andel på 72 % av det industrielle tømmervolumet som ble solgt i 2019. Imidlertid er gran spesielt utsatt for rotråtesopper, som reduserer verdien av virket. Studier basert på data fra Landsskogtakseringer viser at den nasjonale råtefrekvensen i gran i Norge ligger et sted mellom 7.9-9.5 %. Andre studier har vist at omtrent 1 av 5 grantrær er infisert med rotråte. Uavhengig av hvor stor andelen faktisk er, forårsaker råte et estimert verditap på omkring 100 millioner norske kroner årlig. Disse tapene kommer som en følge av reduksjon av virkesverdier, blant annet når en hogstmaskinfører må bulte deler av en stamme. Når hogstmaskinføreren bulter, er det uvisst hvor langt rotråten strekker seg oppover i stammen. Derfor er det behov for en praktisk prediksjonsmodell som kan hjelpe til i prosessen med å håndtere gran med rotkjuke eller honningsopp. Å utvikle denne modellen var hovedmålsettingen med denne studien.M-S

Heat-driven snow production

Global warming is causing increased temperatures and reduced snow cover, which threatens the possibility to exercise winter sports activities near populated areas in the future. Temperature Independent Snow (TIS) production can contribute to increase the snow reliability for winter sport. However, this method is very energy intensive and to reduce operational costs the use of heat instead of electricity as energy source is a potential solution. Absorption appears to be most promising among the possible heat driven refrigeration technologies. Heat supply temperatures can be as low as 85-90°C, which opens the possibility for using district heating. Calculations showed that a thermally driven refrigeration system for TIS production is more than twice as energy intensive compared to using electricity and will depend on low energy costs to be competitive. The review of potential heat sources shows that there is a potential for utilization of district heating and industrial waste heat. District heating is the most prevalent and about 40 % of the identified winter sport facilities are in municipalities where this is offered. However, low temperatures and lack of available heat are potential challenges. Industrial waste heat exists in large quantities at sufficient temperature levels but is less co-located with the winter sports facilities. Furthermore, there are important factors related to cost and technology, which can limit the potential for utilization

Predicting the Extent of Root and Butt rot in Stems of Norway Spruce (Picea abies)

Commercially, Norway spruce (Picea abies (L.) Karst) is the most important tree species in Norway, representing 72% of the industrial timber volume sold in 2019. However, Norway spruce is particularly prone to infection of root and butt rot pathogens, degrading the value of the resource. Studies using National Forest Inventory Data (NFI) show that the nationwide rot frequency of Norway spruce is somewhere between 7.9-9.5%. Other studies have indicated that the presence of root and butt rots are in proportions of approximately 1 out of 5 Norway spruce trees. Root and butt rots cause substantial annual economic losses estimated at NOK 100 millions. The losses are related to degradation of timber resources, per instance, culled by the harvester operator. However, the extent of which the root and butt rots develops up the stem is not known by the harvester operator. Therefore, developing a practical prediction model for rot heights in Norway spruce, to guide the operator in decision making, was addressed in this thesis. The data sampling was carried out on three different occasions. In the first sampling, root and butt rot infected spruce trees were identified. Secondly, the trees were cut to examine the extent of rot in the stems. At last, tree-specific measurements were gathered. The prediction model could explain approximately 21% of the variance in the dataset. Individually, the independent variables diameter at root, proportion of rot and tree height, showed a positive relationship to the prediction of rot height, with increasing values increasing the prediction of rot height. In the evaluation of the prediction model using optimal bucking, a total utilization grade of 76% was discovered. On tree level, the utilization grade was 74% with a standard error of 18%

Power Plant with CO2 Capture based on PSA Cycle

Two coal-fired power plants with CO2 capture by Pressure Swing Adsorption (PSA) havebeen modeled and simulated. The two power plants considered were IntegratedGasification Combined Cycle (IGCC) and conventional Pulverized Coal Combustion (PCC). Amathematical model of the PSA process for each of the power plants was developed and thegoal was to evaluate the feasibility of PSA as a technology for decarbonisation. Theperformance with CO2 capture by PSA was compared to a reference plant without CO2capture and to a power plant with CO2 capture by absorption, which is considered as thebenchmark technology. The size and number of the PSA columns were estimated todetermine the footprint.For the PCC power plant, the PSA model was a two-stage process consisting of a front and a tail stage. Two-stages mean that it consisted of two consecutive PSA processes. The front stage was a three-bed, five-step Skarstrom process with rinse. The tail stage was a two-bed, five-step Skarstrom process with pressure equalization. Zeolite 5A was used as adsorbent. For a specified capture rate of 90.0 %, the process achieved a purity of 96.4 % and a specific power consumption of 1.3 MJ/kgCO2. The net plant efficiency dropped 16.6 percentage points from 45.3 % to 28.7 % when introducing CO2 capture by PSA. In comparison, the PCC plant using absorption achieved a net plant efficiency of 33.4 %. The results indicate that the current state of the art PSA technology for decarbonisation as an alternative to absorption is not realistic for PCC power plants.For the IGCC power plant, the PSA model was a seven-bed, twelve-step Skarstromconfiguration with four pressure equalization steps using activated carbon as adsorbent. The process achieved a purity of 87.8 % and a capture rate of 86.3 % with negligible power consumption. The PSA process did not satisfy the performance targets of 90 % recovery and 95.5 % purity, and due to the low purity it is uncertain whether or not transport and storage of CO2 is at all feasible. The net plant efficiency dropped 12.5 percentage points from 47.3 % to 34.8 %. In comparison the IGCC plant with absorption achieved a net plant efficiency of 36.4 %. The results showed that PSA as a capture technology for IGCC power plants could not perform quite as well as absorption. However, PSA as a capture technology could have a potential if the purity could be increased, and is therefore more promising than PSA for PCC power plants

Heat-driven snow production applying ejector and natural refrigerant

An effect of climate change is fewer cold days and less natural snow at lower elevations. This has spurred the interest in temperature independent snow (TIS) production, i.e., refrigeration technologies that can produce snow at ambient temperatures above zero. Commercially available TIS systems require a higher power consumption than conventional systems, i.e., snow lances and guns. Thus, to ensure that future snow-making sites are sustainable, it is necessary to develop solutions with a minimal environmental footprint. One possibility is to utilize surplus heat from industrial processes or from a district heating network to drive snow-making systems. Examples of heat driven refrigeration technologies fit for this purpose are absorption cooling and ejector cooling, both applying natural refrigerants. This paper evaluates a solution for heat driven ejector-based snow making systems: a vacuum ice slurry system using water (R718) as refrigerant. The required amount of driving heat and its required minimum temperature level largely depend on the ejector characteristics. Thus, to enable a proper evaluation, detailed numerical simulations of the ejector design and its efficiency were performed, at different temperature levels of driving heat and ambient temperatures. Results were used as input to estimate the overall performance, in terms of specific energy consumption (per m3 produced snow), compared to other TIS systems. The ejector-based system can be driven by low-grade heat (80 °C) and is shown to be highly efficient if cold cooling water (≤ 10°C) is available

Integrated high temperature heat pumps and thermal storage tanks for combined heating and cooling in the industry

This study investigates the integrated heat pump system of a green-field dairy located in Bergen, Norway. The purpose of the study is to determine the energy consumption and system performance. The dairy features a novel and innovative solution of a fully integrated energy system, employing high temperature heat pumps such as the hybrid absorption-compression heat pump (HACHP) with natural refrigerants to provide all temperature levels of heating and cooling demands. To evaluate the performance an energy analysis has been performed based on available process data for a comparatively energy-intensive week in February. The results have shown that the integrated system is able to meet the occurring demands. Furthermore, the specific energy consumption with 0.22 kWh l−1 product can outperform the annual average value of the replaced dairy even under difficult conditions. However, it is expected that the specific energy consumption will be further reduced on an annual basis. Through measures such as the extensive use of waste heat recovery accounting for 32.7% of the energy used, energy consumption was reduced by 37.9% and greenhouse gas (GHG) emissions by up to 91.7% compared to conventional dairy systems. Simultaneous, the process achieves a waste heat recovery rate of over 95%. Furthermore, demand peaks were compensated and a system coefficient of performance (COP) of 4.1 was achieved along with the identification of existing potential for further improvements.publishedVersio