Thermal modelling and evaluation of borehole heat transfer.
Doctoral thesis, 2012
The use of ground source heat pump systems to provide heating and cooling in
buildings has increased greatly in the last decade or so. These systems have a high
potential for energy efficiency, which has environmental and economic
advantages. Moreover, the energy efficiency of the ground source heat pump
systems can be further enhanced by optimizing the performance of the system.
However, a key obstacle to the performance optimization of ground source heat
pump systems is the scarcity of mathematical models that can rapidly, yet
accurately, simulate the dynamic thermal response of the borehole system.
This study aims to develop analytical models and methods that can simulate the
thermal response of a borehole system in time scales from minutes to years. An
analytical solution to model the short-time response of the borehole system is
presented. The solution studies the heat transfer problem in the Laplace domain
and provides an exact solution to the radial heat transfer problem in the borehole.
A finite-length line-source solution to determine the long-term response of the
borehole system is also presented. The line-source solution can be used for
modelling both single and multiple borehole systems. The analytical and finitelength
line-source solutions were combined to obtain step-response functions for
various configurations of borehole systems. The step-response functions are valid
from short (hours) to long (years) periods. A load aggregation method is also
presented to speed up the simulations of the borehole systems. All the proposed
models and methods can be easily implemented in any building energy simulation
software to optimize the overall performance of ground source heat pump
The study also analyzes various aspects of the thermal response testing and
evaluation of borehole systems. A ground source heat pump test facility with nine
boreholes was used for the experimental investigations. Several thermal response
tests were conducted for issues that include random variations between tests,
sensitivity of system design to uncertainties in test results, convective heat
transport in boreholes, and recovery times after a test. The evaluations of multiinjection
rate tests on groundwater-filled boreholes were also extensively studied.
Recommendations regarding each of these issues are suggested to improve the
testing and evaluation procedure of borehole systems.
ground source heat pump
thermal response test
ground heat exchanger
Room EE, Hörsalsvägen 11, 6th floor
Opponent: Dr Simon Rees, Inst of Energy and Sustainable Development, De Monfort University, Leicester, England