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Capacity control in ground source heat pump systems part II: Comparative analysis between on/off controlled and variable capacity systems
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.ORCID iD: 0000-0001-7354-6643
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.ORCID iD: 0000-0003-3896-2443
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
2011 (English)In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 34, no 8, 1934-1942 p.Article in journal (Refereed) Published
Abstract [en]

In the present paper, as the second part of two, modeling and simulation was carried out for a Ground Source Heat Pump (GSHP) system in the presence of all the most important interacting sub-systems such as building, ground heat source, electrical auxiliary heater, and the heat pump unit in order to make a fair and comprehensive comparison between the annual performance of on/off controlled and variable capacity systems. The annual modeling showed that dimensioning of the on/off controlled GSHP based on the peak heat demand of the building plays a significant role when the two control strategies are compared: if the on/off controlled GSHP is dimensioned to cover only 55% of the peak heat demand of the building, the electrical auxiliary, which then covers about 10% of the annual heating demand of the building, makes the SPF of the on/off controlled GSHP to be lower than the one of the variable speed system. On the contrary, when the on/off controlled system is dimensioned to cover more than 65% of the building's peak heat demand, i.e. more than 95% of the annual heat demand of the building, there is no considerable difference between the SPFs of the on/off controlled and variable capacity systems.

Place, publisher, year, edition, pages
2011. Vol. 34, no 8, 1934-1942 p.
Keyword [en]
Heat pump, Control, Modelling, Simulation, Variable speed
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-55241DOI: 10.1016/j.ijrefrig.2011.05.012ISI: 000297826500023Scopus ID: 2-s2.0-80955133856OAI: oai:DiVA.org:kth-55241DiVA: diva2:474529
Note
QC 20120109Available from: 2012-01-09 Created: 2012-01-02 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Capacity-controlled Ground Source Heat Pump Systems for Swedish single-family dwellings
Open this publication in new window or tab >>Capacity-controlled Ground Source Heat Pump Systems for Swedish single-family dwellings
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The overall objective of this thesis is to develop a structured method to approach the challenge of better understanding the techniques and potential for capacity control in Ground Source Heat Pump (GSHP) systems used in Swedish single-family dwellings. This thesis aims at development of a generic model of the system that can be used for comparative, descriptive, and predictive analysis of capacity controlled GSHP systems in single-family dwellings.

In order to develop the generic model, first, a conceptual model of the reality of interest is developed based on the objective of the model. Second, a quantitative model of the system is developed based on the conceptual model. Third, experimental studies are carried out in order to obtain better understanding of the behavior of the system and its components and also to validate the capabilities of the model. Furthermore, some examples are presented to show how the generic model developed and evaluated at the previous stages can be used to address the questions in the context of capacity control in GSHP systems.

As the first example of applications of the generic model, a comparative analysis is made between the annual performance of on/off-controlled and variable-capacity GSHP systems. The results show that dimensioning of the on/off-controlled GSHP unit based on the peak heat demand of the building plays a significant role when the annual performance of the on/off controlled GSHP system is compared with that of the variable speed GSHP system. As the second example, another comparative analysis is performed, this time to compare three common methods whose purpose is to control on/off-controlled GSHP system. Based on the results from the detailed analysis of these three control methods, it is recommended not to use the constant hysteresis method to avoid large supply temperature oscillation or large deviation from the required temperatures.

Finding a proper brine mass flow rate, either variable or constant, is a challenge when a variable capacity heat pump system (a heat pump system equipped with a variable speed compressor) is designed. Therefore, as the third example of applications of the generic model, analysis is performed on a variable-capacity GSHP system equipped with a variable speed compressor and variable speed pump in U-pipe borehole heat exchanger. The results show that a single speed liquid pump but with a very carefully-selected brine mass flow rate would be still an appropriate option for variable speed heat pump systems, if COP maximization is the main concern.

Finally, as the fourth example, the performance of a run-around coil heat recovery system equipped with a variable capacity heat pump unit is evaluated over a year. The results show that by retrofitting a well-sized variable capacity heat pump unit to the system, there is a potential to increase the amount of heat provided by the recovery system by more than 70%.

In addition to the examples shown, the systematic approach and the generic model used in the present study can be applied to improve other control techniques and strategies and find new opportunities which can lead to saving energy and money, reducing the greenhouse gas emissions, and gaining higher credibility for GSHPs in the market.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xiv, 90 p.
Series
Trita-REFR, ISSN 1102-0245 ; 12:03
Keyword
Heat Pump, Capacity control, ground, ground source, geothermal
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-102055 (URN)978-91-7501-474-6 (ISBN)
Public defence
2012-09-24, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
effsys2 and effsys+
Note

QC 20120907

Available from: 2012-09-07 Created: 2012-09-07 Last updated: 2012-09-07Bibliographically approved

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Madani, HatefClaesson, Joachim

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