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| 2. |
- Boss, Annika, et al.
(författare)
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Uppvärmning och kylning av lokaler ur energi- och miljömässigt samt ekonomiskt perspektiv
- 2009
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Rapport (refereegranskat)abstract
- Demand for cooling of commercial buildings is increasing and there is a potential for expanding district cooling systems, especially in district heating areas. Using district heating and district cooling has been compared to heat pump techniques. Primary energy, environmental influence and economy have been evaluated. Four buildings in Gothenburg have been included in the study and certain differences have been found depending on demands of heating and cooling, which vary according to design and activity. The results are specific for Gothenburg due to the combination of production methods for district heating and cooling and the pricing, which differ compared to other places. Different perspectives on production of electricity, district heating and district cooling, e.g. average or marginal production, is of vital importance when comparing environmental influence. In most of the case studies the demand of primary energy is lower for district heating and cooling compared to heat pump systems. With a marginal perspective district heating and cooling will lead to lower emissions of greenhouse gases. Using the perspective of average production will on the other hand rate heat pump systems to have a lower influence on the greenhouse effect in most of the cases. Which technique is the most cost efficient depends mainly upon relation of heating and cooling demands. Where there is a greater demand for cooling than for heating, district heating and cooling is more advantageous. It is a need for improved data in commercial buildings from reliable field measurements. The quality of the evaluation is very much dependent on reliable measured data from real installations.
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| 4. |
- Haglund Stignor, Caroline
(författare)
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Comparison of energy use and cost in different indirect cooling systems
- 2007
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Rapport (refereegranskat)abstract
- A case study has been performed comparing 11 different cases of indirect cooling systems in supermarkets. The influence of the selection of cooling-coil / heat exchanger design, display cabinets, type of secondary refrigerant, types of valves, types of pumps and type of system design has been investigated. The cases have been selected to be representative for a large number of supermarkets in Sweden. However, some of the cases are only hypothetical and do no not exist in reality so far. The results show that savings of both energy and money can be significant, by the selection of efficient components and system design. An iterative procedure, for finding the optimal operating point (liquid inlet temperature and liquid flow rate) is suggested. This procedure has been evaluated with good results.
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| 7. |
- Haglund Stignor, Caroline, et al.
(författare)
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Energy-efficient flat-tube heat exchangers for indirectly cooled display cabinets
- 2009
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Ingår i: International Journal of Refrigeration. - : Elsevier BV. - 0140-7007. ; 32:6, s. 1460-1471
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Tidskriftsartikel (refereegranskat)abstract
- Different designs of flat-tube heat exchangers with plain fins have been evaluated theoretically in a parameter study in order to evaluate their performance potential in indirectly cooled display cabinets. Two different types of flat-tube heat exchangers were considered; one with serpentine fins and one with continuous plate fins. Both flat-tube heat exchanger types were adapted to the laminar flow regime on the liquid as well as on the air side. The performance of the two heat exchanger types had previously been verified experimentally under dehumidifying conditions. The results from this parameter study show that considerable savings in the required electric drive power to compressors, pumps and fans can be obtained in comparison with the traditional cooling coil. The savings may be up to 15%. In addition, the required temperature difference for the flat-tube heat exchangers is so small that frost-free operation is possible, which would result in even larger savings. (C) 2009 Elsevier Ltd and IIR. All rights reserved.
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| 9. |
- Haglund Stignor, Caroline
(författare)
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Laminar-flow Liquid-to-air Heat Exchangers - Energy-efficient Display Cabinet Applications
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Provisions are stored and displayed in supermarkets and grocery stores, at a temperature lower than the ambient, in display cabinets, which are responsible for a significant amount of the energy use in this sector. During the 1990s, major changes in the regulations governing the use of synthetic refrigerants took place in Sweden. This resulted in many refrigeration systems being converted to systems with indirect cooling by means of a liquid secondary refrigerant. The cooling coil is an important component in a display cabinet and traditionally, different kinds of tube-coils, with aluminium fins on expanded circular copper tubes, have been used. Many secondary heat transfer media have relatively high viscosities at low tem¬peratures, and so the flow regime is often laminar, which may lead to poor heat transfer. However, it is possible to achieve high heat transfer coefficients even for laminar flows if an ap¬propriate design of the heat exchanger is applied. Flat-tube heat exchangers have been used for a long time in automotive applications, where compactness is important. The display cabinet application involves low air velocities in combination with condensation of water vapour, and sometimes even frosting, and is therefore different from other applications where flat-tube heat exchangers have been used earlier. The objective of this research work has been to find a suitable, more energy-efficient, heat exchanger design for indirectly cooled display cabinets. An efficiency that would mean that temperature differences would be so small that frosting could be avoided was aimed for. This research work has sandwiched experimental investigations with theoretical modelling and parameter studies. Initially, the heat transfer and pressure drop performance of conventional cooling coils operating with liquid secondary refrigerants was studied in full-scale experiments. Thereafter, the liquid-side (or tube-side) heat transfer was studied experimentally in small-scale experiments on three single multiport extruded flat tubes with different cross-sections. In both studies, the best agreement was found with predictions using the Gnielinski correlation for thermally developing laminar flows with the constant temperature boundary condition. After this, two different heat exchangers having flat tubes and plain fins on the air side were evaluated experimentally - one with continuous plate fins and one with serpentine fins. The results show that, for conditions similar to those of display cabinets, the heat transfer and pressure drop performance is affected to little or no extent by the occurrence of condensate water. Models for different types of flat-tube heat exchangers were thereafter created using the results from the experimental studies. In order to find appropriate optimising criteria for the display cabinet heat exchangers, the energy efficiency of a complete cooling system of an imagined supermarket has been studied. Finally, different designs of flat-tube heat exchangers with plain fins have been evaluated theoretically in a parameter study. The results show that considerable savings in the required electric drive power can be obtained in comparison with the traditional cooling coil. The savings can be up to 15 %. In addition, the flat-tube heat exchangers could operate with a minimum temperature difference of around 1 K. This makes frost-free operation possible for many display cabinet applications and thereby the savings potential even larger.
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