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Capacity-controlled Ground Source Heat Pump Systems for Swedish single-family dwellings
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.ORCID iD: 0000-0001-7354-6643
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 [en]
Heat Pump, Capacity control, ground, ground source, geothermal
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-102055ISBN: 978-91-7501-474-6 (print)OAI: oai:DiVA.org:kth-102055DiVA: diva2:550553
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
List of papers
1. Capacity control in ground source heat pump systems Part I: modeling and simulation
Open this publication in new window or tab >>Capacity control in ground source heat pump systems Part I: modeling and simulation
2011 (English)In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 34, no 6, 1338-1347 p.Article in journal (Refereed) Published
Abstract [en]

The present paper, as the first part of two, suggests a method to approach the challenge of capacity control in Ground Source Heat Pumps (GSHP). The paper describes the development of a model of the system which includes several sub-models such as the heat pump unit, building, ground source, thermal storage tank, auxiliary heater, and climate. The developed computer model can be used for comparative analysis of different control methods and strategies aiming at the improvement of the system seasonal performance. With this model, on/off controlled and variable capacity GSHPs, with a single speed or variable speed pumps in the systems, can be evaluated in a wide range of operating conditions and more energy efficient methods of the system control can be found. The computer model is developed in the two environments EES and TRNSYS utilizing so-called co-solving technique.

Keyword
Heat pump, Control, Modeling, Simulation, Variable speed
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-40651 (URN)10.1016/j.ijrefrig.2011.05.007 (DOI)000294398000003 ()2-s2.0-79961020524 (Scopus ID)
Note
QC 20110927Available from: 2011-09-27 Created: 2011-09-20 Last updated: 2017-12-08Bibliographically approved
2. Capacity control in ground source heat pump systems part II: Comparative analysis between on/off controlled and variable capacity systems
Open this publication in new window or tab >>Capacity control in ground source heat pump systems part II: Comparative analysis between on/off controlled and variable capacity systems
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.

Keyword
Heat pump, Control, Modelling, Simulation, Variable speed
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-55241 (URN)10.1016/j.ijrefrig.2011.05.012 (DOI)000297826500023 ()2-s2.0-80955133856 (Scopus ID)
Note
QC 20120109Available from: 2012-01-09 Created: 2012-01-02 Last updated: 2017-12-08Bibliographically approved
3. Evaluation of the annual performance of Ground Source Heat Pump systems: A comparison between single speed and variable speed systems
Open this publication in new window or tab >>Evaluation of the annual performance of Ground Source Heat Pump systems: A comparison between single speed and variable speed systems
2011 (English)In: 23rd IIR International Congress of Refrigeration, International Institute of Refrigeration, 2011, 3741-3748 p.Conference paper, Published paper (Refereed)
Abstract [en]

In the present paper, modelling 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 modelling showed that dimensioning of the on/off controlled GSHP based on the peak heat demand of the building plays a significant role when two control strategies are compared: if the on/off controlled GSHP is dimensioned to cover only 57% of the peak heat demand of the building, the electrical auxiliary, which covers about 10% of the annual heating demand of the building, makes the SPF of the on/off controlled GSHP be lower than the one of the variable speed system. On the contrary, when the on/off controlled system is dimensioned to cover about 70% of the building’s peak heat demand, i.e. about 98% of the annual heat demand of the building, the SPF of the on/off controlled system can higher than the variable capacity systems.

Place, publisher, year, edition, pages
International Institute of Refrigeration, 2011
Series
Congres International du Froid-International Congress of Refrigeration, ISSN 1025-9031 ; 23
Keyword
ground source, heat pump, variable speed, single speed, capacity control, control
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-63215 (URN)000310485802020 ()978-2-913149-88-5 (ISBN)
Conference
23rd IIR International Congress of Refrigeration, Prague, Czech Republic, August 21-26 2011
Projects
Effsys+
Note

QC 20120410

Available from: 2012-01-22 Created: 2012-01-22 Last updated: 2014-01-14Bibliographically approved
4. A descriptive and comparative analysis of three common control techniques for an on/off controlled Ground Source Heat Pump (GSHP) system
Open this publication in new window or tab >>A descriptive and comparative analysis of three common control techniques for an on/off controlled Ground Source Heat Pump (GSHP) system
2013 (English)In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 65, 1-9 p.Article in journal (Refereed) Published
Abstract [en]

In the present paper, three common methods in order to control an on/off controlled Ground Source Heat Pump (GSHP) system called "Constant hysteresis", "Floating hysteresis", and "Degree-Minute" methods are comprehensively described. Then, the generic model already developed by the authors is used in order to do the dynamic simulation of the systems with three different control methods over a year and making the comparison between them. The results from annual modeling of the systems show that the mean temperature of the heating water supplied to the building for the system controlled with degree-minute method is always close to the required temperature, regardless of the climatic boundary conditions over a typical year, whereas, the average supply temperature for the system with constant hysteresis method is mostly higher or lower than the required temperature, depending on the boundary condition. Regarding the annual energy use, the degree-minute and constant hysteresis methods have the lowest and highest annual energy use respectively. Switching from constant hysteresis to floating hysteresis method, the annual energy use will become lower and the mean temperature of the heating water supplied to the building will be closer to the required one.

Keyword
Heat pump, Control, Modeling, Simulation, Ground source, Regulation, Geothermal, Capacity
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-102070 (URN)10.1016/j.enbuild.2013.05.006 (DOI)000324449800001 ()2-s2.0-84879484943 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20150630

Available from: 2012-09-07 Created: 2012-09-07 Last updated: 2017-12-07Bibliographically approved
5. The Ground Source Heat Pump: A System Analysis With a Particular Focus on The U-Pipe Borehole Heat Exchanger
Open this publication in new window or tab >>The Ground Source Heat Pump: A System Analysis With a Particular Focus on The U-Pipe Borehole Heat Exchanger
2010 (English)In: 2010 14th International Heat Transfer Conference, Volume 4, 2010, 395-402 p.Conference paper, Published paper (Refereed)
Abstract [en]

The mass flow rate of the secondary refrigerant flowing in the borehole heat exchanger of a ground source heat pump is an influential system parameter whose variation can influence the pumping power, efficiency of the pump, heat distribution in the borehole, heat pump heat capacity, and above all, the system Overall Coefficient Of Performance (COP). The present paper uses both in-situ field measurements and modeling to evaluate these effects. From the field measurements, it can be concluded that the thermal contact between U-pipe channels increases as the brine mass flow rate decreases. Furthermore, the modeling results show that there is a certain optimum brine mass flow rate which gives a maximum overall system COP. Different optimum mass flow rates are obtained for different compressor speed and it is shown that their relation is almost linear. However, concerning system COP maximization, it can be concluded that a constant but carefully-selected brine mass flow rate can still be an appropriate option for the variable capacity heat pump unit studied in the present paper where the compressor frequency changes between 30Hz and 75Hz. Concerning the heat capacity maximization in the system, a variable speed brine pump can be used to help the insufficiently-sized compressor to cover the peak heat demand of the building.

National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-87252 (URN)10.1115/IHTC14-22395 (DOI)000307206500048 ()2-s2.0-84860501049 (Scopus ID)
Conference
2010 14th International Heat Transfer Conference (IHTC14) August 8–13, 2010 , Washington, DC, USA
Note

QC 20120418

Available from: 2012-02-14 Created: 2012-02-14 Last updated: 2013-06-11Bibliographically approved
6. Retrofitting a variable capacity heat pump to a ventilation heat recovery system: modeling and performance analysis
Open this publication in new window or tab >>Retrofitting a variable capacity heat pump to a ventilation heat recovery system: modeling and performance analysis
2010 (English)Conference paper, Published paper (Other academic)
Keyword
Run-around coil, ventilation heat recovery, heat pump, variable speed, variable capacity, modelling
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-102072 (URN)
Conference
International Conference on Applied Energy
Note

QC 20120907

Available from: 2012-09-07 Created: 2012-09-07 Last updated: 2012-09-07Bibliographically approved
7. Run-around coil ventilation heat recovery system: A comparative study between different system configurations
Open this publication in new window or tab >>Run-around coil ventilation heat recovery system: A comparative study between different system configurations
2012 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 90, no 1, 258-265 p.Article in journal (Refereed) Published
Abstract [en]

The energy performance of buildings in cold climates, with a considerable annual heating demand, is dependent on the ventilation air change rates (ACH). Buildings utilized for commercial use often have high annual ventilation heating demand due to high ACH required from indoor air quality aspect. In order for these buildings to have a reasonable energy performance a heat recovery system is often used to recover heat from the exhaust air to the makeup air. There are different variations of these systems; one that is sometimes used in Sweden is a run around coil heat recovery system. The present paper summarizes the findings from previous studies [5-7], and presents a comparative study, for three different cases; the traditional run-around coil heat recovery system; with a three stage on/off controlled heat pump retrofitted into the system; and with a variable capacity heat pump retrofitted into the system. Annual modeling (using TRNSYS) shows that by retrofitting a well-designed 3 stage heat pump to the system the annual heat recovery rate for the Stockholm case can be increased from 47% to 65%. For a retrofitted variable speed capacity heat pump for the Stockholm case the annual heat recovery improves from 47% to 66%. The modeling also shows that a well designed variable speed heat pump can cover 81% of the total ventilation heating demand and a well designed multi stage heat pump 77% of the total ventilation heating demand.

Keyword
Run-around coil, Ventilation heat recovery, Performance factors, Retrofitted heat pump
National Category
Energy Systems
Identifiers
urn:nbn:se:kth:diva-58808 (URN)10.1016/j.apenergy.2011.05.012 (DOI)000297426100039 ()2-s2.0-80055039757 (Scopus ID)
Note
QC 20120109Available from: 2012-01-09 Created: 2012-01-09 Last updated: 2017-12-08Bibliographically approved

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