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Maldistribution in air-water heat pump evaporators. Part 2: Economic analysis of counteracting technologies
Danfoss AS Refrigerat & Air Conditioning, Denmark.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.ORCID iD: 0000-0002-9902-2087
2015 (English)In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 50, 217-226 p.Article in journal (Refereed) Published
Abstract [en]

In this study a methodology is applied to quantify the effect of evaporator maldistribution on operating costs of air-water heat pumps. The approach is used to investigate the cost-effectiveness of two technologies enabling to counteract maldistribution: a flash gas bypass setup and the individual superheat control in parallel evaporator channels. In the total cost of ownership analysis, different scenarios for climatic conditions, severity of maldistribution, and economic framework are considered. Results show that the flash gas bypass system is cost-effective only in a few conditions, namely severe maldistribution, high electricity prices, and colder climate. Investment in the individual superheat control technology, however, can be quickly amortized in many scenarios. For the warmer climate zone with a small number of operating hours counteracting of maldistribution does not pay off under the used economic assumptions.

Place, publisher, year, edition, pages
2015. Vol. 50, 217-226 p.
Keyword [en]
Annual performance, Heat pump, Maldistribution, Optimization, Total cost of ownership
National Category
Energy Engineering
URN: urn:nbn:se:kth:diva-162096DOI: 10.1016/j.ijrefrig.2014.07.005ISI: 000350091900022ScopusID: 2-s2.0-84922242641OAI: diva2:796892

QC 20150327

Available from: 2015-03-20 Created: 2015-03-20 Last updated: 2015-03-27Bibliographically approved
In thesis
1. Economic analysis of air-water heat pump technologies with a screening method
Open this publication in new window or tab >>Economic analysis of air-water heat pump technologies with a screening method
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Early on in the process of product development a decision has to be made which technologies to focus on. Under a purely techno-economic viewpoint for a heat pump only these technologies should be considered which maximize heat pump performance for a given cost. Finding these optima is in practice far from trivial as the result is inuenced by variations in operating conditions, interactions between components, model assumptions and uncertain economic data. The overall objective of this thesis is therefore to develop a screening method for the evaluation and comparison of different technologies in regard of cost and efficiency with the aim to identify optimal heat pump designs.

In practice the applicability of such a method depends on the required effort.  Simple mathematical models and short computation times are as mandatory as reliable, coherent and sufficiently general results. To this end the screening method combines methods of simulation, annual performance calculation, metamodeling and optimization.

The screening method is employed for air-water heat pumps in three utilization examples. In the first example the operational costs of maldistribution in evaporators are quantified. It is shown that for air-water heat pumps increasing the evaporator size is no liable option to counteract maldistribution effects. Two alternative technologies, an adjustment of the cycle layout and a change of the superheat control method, are evaluated under the aspect of total cost of ownership. Only with the second technology noteworthy savings can be achieved compared to the baseline. In the second utilization example on/o_ and variable speed control for regulation of the heat pump capacity are considered. Only for colder climates variable speed control pays o_ for the end consumer in a reasonable time. The study shows the comparison of the two control methods to strongly depend on compressor size. In the third example four different cycle layouts are compared. It is demonstrated that the result of the evaluation depends strongly on practical operating limits and on compressor characteristics. The most promising option is a staged layout with economizer heat exchanger.

Two additional studies consider the modeling of operating conditions in more detail. In the first study the simple approach for calculating annual performance used in the screening method is compared with a comprehensive dynamic model. Optimization for both model approaches results in similar component sizes. In the second study the evaporator model is extended to include a dynamic frost growth model which is used to assess operational costs induced by frosting and defrosting of the evaporator coil. A method to reduce the number of defrosts without negatively affecting heat pump capacity is presented and its feasibility demonstrated with experiments.

The screening method can be extended to include more optimization parameters than used in the presented examples. It can also be applied for other small scale vapor compression systems or it can be integrated in a comprehensive evolutionary optimization procedure to reduce computation time and increase numeric stability. Thus the screening method can be a valuable tool in the product development process for shortening the times until new technologies which safe energy and thereby reduce greenhouse gases are available on the market.


Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xii, 126 p.
TRITA-REFR, ISSN 1102-0245 ; 15:02
National Category
Energy Engineering
urn:nbn:se:kth:diva-162104 (URN)978-91-7595-486-8 (ISBN)
Public defence
2015-04-10, Sal Q2, Osquldasväg 10, KTH, Stockholm, 09:00 (English)

QC 20150324

Available from: 2015-03-24 Created: 2015-03-20 Last updated: 2015-03-24Bibliographically approved

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