Capacity control in Heat Pump systems

The overall objective of this project is to develop a structured method to approach the challenge of better understanding the techniques and potential for capacity control in Heat pump systems with a focus on Ground Source Heat Pump (GSHP) systems.

As the main result of this project, a generic model of the Heat Pump system is developed and used for comparative, descriptive, and predictive analysis of capacity controlled Heat Pump systems.

Methodology

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.

The applications of the generic model

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.

The list of publications

Madani H., Claesson J., Lundqvist P. 2011 “Capacity control in ground source heat pump systems, Part I: modeling and simulation”, International Journal of Refrigeration, Volume 34 (6), Issue 6, pp 1338-1347.

Madani H., Claesson J., Lundqvist P. 2011 “Capacity control in ground source heat pump systems, Part II: Comparative analysis between on/off controlled and variable capacity systems”, International Journal of Refrigeration, Volume 34 (8), pp 1934-1942.

Madani H., Lundqvist P.  2011 “Evaluation of the annual performance of Ground Source Heat Pump systems: A comparison between single speed and variable speed systems”, 23rd IIR International Congress of Refrigeration, Prague, Czech Republic, ID 843.

Madani H., Claesson J., Lundqvist P. “A descriptive and comparative analysis of three common control techniques for an on/off controlled Ground Source Heat Pump (GSHP) system”, submitted to International Journal of Energy and Buildings.

Madani H., J. Acuna, B. Palm, J. Claesson, P. Lundqvist 2010 “The ground source heat pump: a system analysis with a particular focus on the U-pipe borehole heat exchanger” 14th ASME International Heat Transfer conference, Washington, US, ID IHTC-22395.

Madani H., Wallin J., Claesson J., Lundqvist P. 2010 “Retrofitting a variable capacity heat pump to a ventilation heat recovery system: modeling and performance analysis”, International Conference of Applied Energy, Singapore, ID 136.

Wallin J., Madani H., Claesson J.  2012 “Run-around coil ventilation heat recovery system: A comparative study between different system configurations”, International Journal of Applied Energy, Volume 90, Issue 1, pp 258-265.

Madani H., N. Ahmadi, J. Claesson, P. Lundqvist (2010) “Experimental Analysis Of A Variable Capacity Heat Pump System” International Refrigeration and Air Conditioning Conference, Purdue, US, ID 1063.

Wallin J., Madani H., Claesson J. (2010) “Run-around coil ventilation heat recovery system: A comparative study between different system configurations” International Conference of Applied Energy, Singapore, ID 16.

Madani H., P. Lundqvist, J. Claesson (2008) ”Variable capacity heat pump systems, modeling and simulation”, 9th International Energy Agency Heat pump conference, Zurich, Switzerland, ID 4.31.

Madani H. (2009) “Variable capacity heat pump system in a single family house: dynamic modeling and simulation” Journal of federation of European HVAC association (REHVA), issue 11.

Wallin J. H. Madani, J. Claesson, P. Lundqvist (2009) “Ventilation heat recovery with run around coil: System analysis and a study on efficiency improvement – Part I” ASHRAE Region-At-Large conference, Kuwait.

Madani H., J. Wallin, J. Claesson, P. Lundqvist (2010) “Ventilation heat recovery with run around coil: System analysis and a study on efficiency improvement – Part II” ASHRAE Region-At-Large conference, Kuwait.

Contact

Dr. Hatef Madani

Email: hatef.madani@energy.kth.se

Tel: +46 8 790 8653