Experimental investigation on air-source transcritical CO2 heat pump water heater system at a fixed water inlet temperature (original) (raw)
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Experimental investigation of transcritical CO2 heat pump for simultaneous water cooling and heating
2010
This pa per pres ents the ex per i men tal per for mances of a transcritical CO 2 heat pump pro to type for si mul ta neous wa ter cool ing and heat ing ap pli ca tions. Sys tem be hav ior and per for mances such as cool ing ca pac ity, heat ing ca pac ity, and sys tem co ef fi cient of per for mance (COP) have been stud ied ex per i men tally for var i ous oper at ing pa ram e ters such as wa ter mass flow rate, wa ter in let tem per a ture for both evap o ra tor and gas cooler, and ex pan sion valve open ing. Per for mance is also compared with pre vi ous test data. Test in di cates that the ex pan sion valve open ing has a sig nif i cant ef fect as well near the full valve clos ing con di tion (up to 20°). Study shows that both the wa ter mass flow rate and in let tem per a ture have sig nif i cant effect on sys tem per for mances. Test re sults show that, at gas cooler pres sure of 90 bar, the ef fect of evap o ra tor wa ter mass flow rate on the sys tem per for mances is more pro nounced (COP in creases 0.6 for 1 kg/min.) com pared to the gas cooler wa ter mass flow rate (COP in creases 0.4 for 1 kg/min.) and the ef fect of gas cooler wa ter in let tem per a ture is more sig nif i cant (COP de creases 0.48 for given ranges) com pared to the evap o ra tor wa ter in let tem per a ture (COP in creases 0.43 for given ranges).
Energies
A new avenue in modern heat pump technology is related to the use of natural refrigerants such as carbon dioxide (CO 2). The use of CO 2 in direct expansion ground source heat pumps (DX-GSHP) has also gained significant interest as it offers opportunities for cost reduction of the ground loop, albeit some challenges remain in their development, design and use. To address these challenges and to characterize CO 2-DX-GSHP performance for water heating applications, a detailed theoretical model and a fully-instrumented test apparatus was developed and built at CanmetENERGY Research Laboratory. The theoretical model was validated against a set of experimental results and adopted to investigate the performance of the system over a wide operating range. Validation results showed that the model predicts the experimental results within the measurement uncertainty. A detailed system performance analysis was also performed using the theoretical model to understand the system behavior and explore the actions required for performance improvement in future installations. The results of the analysis showed that improper design and control of some components, such as the gas cooler and ground heat exchanger can degrade the system performance by up to 25%, and the heat pump heating capacity by 7.5%.
Simulation of a transcritical CO 2 heat pump cycle for simultaneous cooling and heating applications
A steady state simulation model has been developed to evaluate the system performance of a transcritical carbon dioxide heat pump for simultaneous heating and cooling. The simulated results are found to be in reasonable agreement with experimental results reported in the literature. Such a system is suitable, for example, in dairy plants where simultaneous cooling at 4 8C and heating at 73 8C are required. The optimal COP was found to be a function of the compressor speed, the coolant inlet temperature to the evaporator and inlet temperature of the fluid to be heated in the gas cooler and compressor discharge pressure. An optimizing study for the best allocation of the fixed total heat exchanger inventory between the evaporator and the gas cooler based on the heat exchanger area has been carried out. Effect of heat transfer in the heat exchangers on system performance has been presented as well. Finally, a novel nomogram has been developed and it is expected to offer useful guidelines for system design and its optimisation. q Elimination des cristaux de givre sur une plaque froide: effets des fréquences stationnaires et de balayage des champs électriques
International Journal of Refrigeration-revue Internationale Du Froid, 2004
A steady state simulation model has been developed to evaluate the system performance of a transcritical carbon dioxide heat pump for simultaneous heating and cooling. The simulated results are found to be in reasonable agreement with experimental results reported in the literature. Such a system is suitable, for example, in dairy plants where simultaneous cooling at 4 8C and heating at 73 8C are required. The optimal COP was found to be a function of the compressor speed, the coolant inlet temperature to the evaporator and inlet temperature of the fluid to be heated in the gas cooler and compressor discharge pressure. An optimizing study for the best allocation of the fixed total heat exchanger inventory between the evaporator and the gas cooler based on the heat exchanger area has been carried out. Effect of heat transfer in the heat exchangers on system performance has been presented as well. Finally, a novel nomogram has been developed and it is expected to offer useful guidelines for system design and its optimisation. q Elimination des cristaux de givre sur une plaque froide: effets des fréquences stationnaires et de balayage des champs électriques
Carbon dioxide as refrigerant for tap water heat pumps: A comparison with the traditional solution
International Journal of Refrigeration, 2005
Increased concern about the environmental impact of the refrigeration technology is leading toward design solutions aimed at improving the energy efficiency of the related applications, using eco-friendly refrigerants, i.e. ozone-friendly and with the least possible global warming potential (GWP). In this respect, carbon dioxide (ASHRAE R744) is seen today as one of the most promising refrigerants and is raising great interest in industrial and scientific fields. In the present work, the plant options are investigated, which are related to the design of air/water heat pumps for tap water using CO 2 . A comparison is made, in terms of energy efficiency, between a system working with CO 2 and a similar one working with HFC R134a; such a comparison is carried out by means of a simulation model of a refrigerating machine/heat pump, characterized by a detailed representation of the heat exchangers, based on their subdivision into elementary volumes. Results show that carbon dioxide is an interesting substitute for synthetic fluids, if the design of the system is focused to take advantage of its properties. q
Energies
Although CO 2 as refrigerant is well known for having the lowest global warming potential (GWP), and commercial domestic heat pump water heater systems exist, its long expected wide spread use has not fully unfolded. Indeed, CO 2 poses some technological difficulties with respect to conventional refrigerants, but currently, these difficulties have been largely overcome. Numerous studies show that CO 2 heat pump water heaters can improve the coefficient of performance (COP) of conventional ones in the given conditions. In this study, the performances of transcritical CO 2 and R410A heat pump water heaters were compared for an integrated nearly zero-energy building (NZEB) application. The thermodynamic cycle of two commercial systems were modelled integrating experimental data, and these models were then used to analyse both heat pumps receiving and producing hot water at equal temperatures, operating at the same ambient temperature. Within the range of operation of the system, it is ...
Transcritical carbon dioxide based heat pumps for simultaneous cooling and heating applications
Ozone layer depletion has caused most of the conventional refrigerants used in high temperature heat pumps to be phased-out recently, and a suitable synthetic refrigerant is yet to be found. Several natural refrigerants such as hydrocarbons, water, and carbon dioxide have been presented as alternatives. In this context, environmentally benign transcritical CO 2 cycle based heat pumps offer widespread possibilities in process heat applications due to the large temperature glide present in the gas cooler and can be extensively used in food and dairy, chemical, textile, paper, sugar and other industries where process heat is a critical input. A detailed performance analyses of heat pump systems have been carried out for several types of process heat applications with various possible heat sources. Important performance characteristics of the transcritical CO 2 process have been reviewed along with their optimization aspects. Performance based comparisons have been made between the conventional heat pump systems and CO 2 based ones. Suitability of the CO 2 system in specific process application has been reported; this arises because a particular process application imposes specific temperature and pressure requirements. Results show that although the CO 2 heat pumps give marginally lower COP (5% to 25%) compared to other conventional refrigerants in industrial heat pumps, they offer considerably lower pressure ratios (3 to 4 times) and higher volumetric capacity. It is observed that CO 2 systems have strong potential in process heating and cooling (refrigeration / water cooling / air conditioning / process cooling). It is expected that CO 2 heat pumps will be viable alternatives for process heat application due to its eco-friendliness, higher volumetric capacity and good heat transfer properties.
A simplified method to evaluate the energy performance of CO2 heat pump units
International Journal of Thermal Sciences, 2011
The prediction of the performances of CO 2 transcritical heat pumps demands accurate calculation methods, where a particular effort is devoted to the gas cooler modelling, as the correlation between high pressure and gas cooler outlet temperature strongly affects the cycle performance. The above-mentioned methods require a large amount of input data and calculation power. As a consequence they are often useless for the full characterisation of heat pumps which are sold on the market.