| Techno-Economic Assessment of Dual-Source Heat Pump Systems: Borehole Size Reduction and Life-Cycle Cost Analysis Across Three Cities in CanadaDual-source heat pumps (DSHPs) mitigate high upfront costs of ground-source systems (GSHPs) in by dynamically switching between air and ground sources. This study evaluates DSHP performance and economic feasibility across three Canadian cities (Edmonton, Toronto, and Montreal) through semi-analytical dynamic simulations of DSHP system and life-cycle cost analysis. Lowering the outdoor air temperature set points (0°C, -5°C, -10°C) —above which the heat pump operates in air-source mode and below which it switches to ground-source mode during heating mode—reduces borehole lengths by 4.5–42%, with Toronto achieving the highest savings (42% borehole reduction, 24% capital cost reduction, and 14% net present value (NPV) of costs reduction at -10°C) due to milder climate. University of Alberta | Publication | 2025-05-25 | Nima Mahmoudi Majdabadi, Koohi, S. |
| Metaheuristic optimization of borehole layouts for cost effective ground-source heat pump systemsGround Source Heat Pump (GSHP) systems that are connected to vertical ground heat exchangers (GHEs), also called boreholes, are a sustainable option for heating and cooling buildings, as they make use of the stable temperature of the ground and deliver heating and cooling efficiently. However, the high initial cost, mainly due to drilling boreholes, remains a major challenge. One of the most practical ways to reduce this cost is by decreasing the total length and number of boreholes while still meeting GSHP system requirements. The goal of this work is to find practical and efficient ways to design GHE layouts that are more affordable and easier to implement in larger projects without affecting system performance. This is done by keeping the borehole running fluid temperature that is in connection with the GSHP within acceptable limits during both heating and cooling, and ensuring that borehole lengths do not exceed a set limit, here 250 meters (820 ft). An optimization procedure is proposed based on a regular arrangement of boreholes to determine the required borehole numbers following current design practice. Then, a genetic algorithm is applied to rearrange the positions of these boreholes to further reduce the total borehole (and drilling) length. It was concluded that optimizing the layout with fewer boreholes than in the base case yielded better results, with the algorithm achieving a 6% reduction in total drilling length. University of Alberta | Activity | 2025-10-06 | Farzad Dadbakhsh, Koohi, S. |
| Optimizing Borehole Configurations to Reduce Drilling Costs in Ground Source Heat Pump Systems University of Alberta | Activity | 2026-01-18 | Farzad Dadbakhsh, Koohi, S. |
| Techno-Economic Analysis of Ground-Source and Dual-Source Heat Pumps for Canadian ClimatesGround-source heat pumps (GSHPs) are a cornerstone technology for decarbonizing building
heating and cooling. However, two key challenges limit their broader adoption: uncertainty in
long-term performance under evolving subsurface temperature conditions and high initial capital
costs driven by extensive borehole drilling requirements. This mixed-format thesis comprises
two complementary studies, each targeting one of these challenges.
The first study develops a semi-analytical dynamic GSHP model that integrates three core
components: a detailed vapor-compression cycle resolving heating/cooling capacity and
coefficient of performance (COP) variations with heat pump entering liquid temperature (ELT)
from the ground. Validation is carried out against heat pump manufacturer data, published
numerical simulation results, and OpenModelica simulations. Using this framework, the
influence of both internally and externally induced ground temperature variations on ground-
source heat pump heating and cooling capacities, and its COP over multi-year operation is
quantified. A case study for a heating-dominated building load reveal that while cooling capacity
changes only ~0.5% per one temperature degree (°C) increase in ground temperature, heating
capacity declines by ~3% per one temperature degree (°C) decrease. To understand the
significance of such capacity declines in the ground-source heat pump as a result of ground
temperature variations, it is shown that a ground temperature reduction of 2 °C or more results in
unmet peak heating loads requiring auxiliary systems. Monte Carlo uncertainty analysis
combined with partial Spearman rank correlation sensitivity analysis identifies soil and grout
conductivities as dominant parameters, while ground heat exchanger (GHE) running fluid
properties exert weaker effects. These findings demonstrate the necessity of incorporating
realistic subsurface dynamics for reliable long-term GSHP design and operation.
The second study investigates dual-source heat pumps (DSHPs), which switch between air and
ground operation based on outdoor temperature setpoints, as a strategy for reducing borehole
length and GSHP capital and life-cycle costs in cold climates. A dynamic DSHP model is
developed in OpenModelica. This configuration accurately resolves short-term borehole
transients during frequent switching between air and ground sources. Techno-economic analyses
of DSHPs are performed for Edmonton, Toronto, and Montréal, considering both small-scale and
large-scale systems. Results show that DSHPs can reduce borehole design length by up to
approximately 40% and lower capital cost by approximately 24%, while still achieving positive
net present value (NPV) life-cycle cost savings up to approximately 15% despite reduced COP in
air-source mode of the heat pump operation. A Monte Carlo uncertainty analysis confirms the
robustness of the economic advantage, with partial Spearman sensitivity analysis revealing
borehole cost, heat pump cost, and interest rate as the dominant financial drivers, with inflation
having the least impact.
Together, these studies provide a validated, computationally efficient medium- to long-term
dynamic GSHP modeling framework that captures capacity and COP sensitivities to subsurface
temperature drift, as well as a techno-economic assessment of DSHP systems demonstrating that
strategic air–ground switching can significantly reduce borehole length and life-cycle costs of
GSHP systems in cold climates. This thesis advances GSHP/DSHP performance prediction via a
techno-economic assessment in Canadian cold climates, and establishes a generalizable
foundation for accelerating GSHP deployment. | Publication | 2025-09-30 | Nima Mahmoudi Majdabadi |
| A review of environmental assessments of ground-source heat pumpsGround source heat pumps (GSHPs) are considered to be a promising technology to improve the energy efficiency of heating and cooling in buildings. However, sustainability of heat pump technologies and in particular GSHPs can sometimes be questioned. Detailed investigation of the environmental impacts of GSHPs over all stages of their life is needed to evaluate their sustainability. In this article, studies focused partially or in full on the environmental impact assessment of GSHPs, and their integrations with other systems, are reviewed. The focus of the review is on the main findings of such studies to provide a clearer picture of their status, but a summary of data input and methodologies that are used in such studies is also provided to ensure meaningful comparisons can be made among results of various studies, and to guide new studies on environmental assessment of GSHPs. It is found through this review that the main life stage contributing to environmental impacts of GSHPs is operation stage and the main contributor during this stage is electricity generation mix. Improvements in electricity generation source seem to be the most important factor to be considered if a wider adoption of GSHPs is sought. University of Alberta | Publication | 2024-12-08 | Koohi, S. |
| A Semi-Analytical Dynamic Model for Ground Source Heat Pump Systems: Addressing Medium- to Long-Term Performance Under Ground Temperature VariationsAs the demand for sustainable heating, ventilation, and air conditioning
(HVAC) solutions increases due to climate change and energy efficiency concerns,
Ground-Source Heat Pumps (GSHPs) have emerged as a promising technology.
However, GSHP performance is significantly influenced by temperature variations under
the ground. The overall objective of this study is to evaluate the impact of ground
temperature dynamics on GSHP performance by proposing a semi-analytical dynamic
model capable of simulating medium- to long-term heat pump operations. The proposed
model accounts for the interactions between the Ground Heat Exchanger (GHE) and the
heat pump, enabling accurate predictions of system performance over extended periods.
A case study using the proposed model demonstrates how ground temperature
variations from external factors affect the coefficient of performance (COP) and the
heating and cooling capacity of GSHP systems. University of Alberta | Publication | 2025-06-11 | Nima Mahmoudi Majdabadi, Koohi, S. |
| Integration of air-source to ground-source heat pump systems: Impact on borehole design and life-cycle cost in Canada University of Alberta | Publication | 2026-06-15 | Nima Mahmoudi Majdabadi, Misagh Irandoostshahrestani, Koohi, S. |
| Metaheuristic optimization of borehole layouts for cost-effective ground-source heat pump systemsThe economic viability of ground source heat pump (GSHP) systems is strongly influenced by the design of vertical ground heat exchangers (GHEs), as borehole drilling constitutes a major portion of the initial installation cost. Although GSHP systems provide efficient and sustainable heating and cooling by exploiting the thermal stability of the ground, reducing the total borehole field (often called borefield) drilling length remains a key challenge, particularly for large-scale applications. In this study, an optimization-based design framework is proposed using ground heat conduction analysis to reduce the total required borehole length while maintaining long-term heat pump performance. A reference design is first established using a conventional regularly spaced borehole arrangement in accordance with standard design practice to determine the required number of boreholes. Then, a genetic algorithm is employed … University of Alberta | Publication | 2026-08-26 | Farzad Dadbakhsh, Koohi, S. |
| Optimization of Borehole Layouts in Ground Source Heat Pump Systems Using Metaheuristic Algorithms University of Alberta | Publication | 2026-01-31 | Farzad Dadbakhsh, Koohi, S. |
