Frequency Domain Modeling of Heat Transport around Borehole Heat Exchangers

Research output: Chapter in Book/Report/Conference proceedingMeeting abstract (Book)

Abstract

Ground coupled heat pump (GCHP) systems provide an energy-efficient alternative to traditional air-conditioning systems for space heating and cooling. Heat is extracted from or injected into the ground through vertical borehole heat exchangers, which form a so-called borefield. The energy efficiency of the GCHP depends on the temperature of the fluid entering the GCHP at the borefield side. In other words, the temperature of the fluid coming out of the borehole influences the energy efficiency of the GCHP. Thus, the knowledge of this temperature is important to develop a control strategy that minimizes the energy consumption. That is why we aim to find an accurate model for the relation between the thermal (heating or cooling) load of the ground and this temperature. The thermal response test was introduced by Mogensen P. [1] to determine the main thermal characteristics of the ground (resistance and conductance) that relate the thermal load to the temperature. Analytical or numerical [2, 3] techniques were developed to find estimates for these characteristics. However, all the developed techniques make use of approximations. The analytical techniques simplify the heat transfer problem into a line- or cylindrical- source problem in order to be able to find an analytical solution. This makes these techniques well suited to model the relation on a long time scale (> 24h). However, the short term response is less accurate and a constant heat input is required. The numerical techniques can handle both long and short time scales and variable heat input. However, both analytical and numerical techniques start from an approximate heat conduction equation, where in general the heat convection is neglected for simplification purposes. The relation between the load and the temperature will be estimated with a rational model (black-box) in the frequency domain. No assumptions for the parameters of this model will be made. This approach will lead to a model that reflects the relation between the temperature and the load present in the measurement data. The interpretation of the estimated model is less intuitive than the one found with the standard analytical and numerical approaches, but the model is expected to be more accurate on the short time scale (<24h). In a following step, this more accurate model can be used to develop a control strategy that minimizes the energy consumption.
Original languageEnglish
Title of host publicationERNSI'2012, European Research Network on System Identification, 23-26 September 2012, Maastricht, The Netherlands
Publication statusPublished - 23 Sep 2012
EventERNSI'2012, European Research Network on System Identification - Maastricht, Netherlands
Duration: 23 Sep 201226 Sep 2012

Conference

ConferenceERNSI'2012, European Research Network on System Identification
CountryNetherlands
CityMaastricht
Period23/09/1226/09/12

Keywords

  • Ground coupled heat pump (GCHP) systems

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