Renewable Geothermal Energy

RA: Hongwei Liu (MSc Student) & Yu Yan Li (Undergraduate Student)

Project Duration: 2016 – 2018

Collaborators & Partnerships: Ako Bahari (Department of Mechanical Engineering) & Dr. Miroslava Kavgic (Department of Civil Engineering)

Financial Support: University of Manitoba Startup Fund

Project Description: 

Snow accumulation on pavement slabs and bridge decks during winter causes tremendous inconvenience for drivers and traffic accidents. For example, almost 30% of car accidents in Canada occur due to snowy or icy roads. A traditional approach for snow melting and de-icing of pavement slabs and bridge decks is to use salt and other kinds of chemical materials, which can lower the freezing point of water to prevent the formation of ice. Unfortunately, this method can cause some problems. Salt will not only be ineffective for snow melting or de-icing if temperature falls below -3.9 °C, but also penetrate down to the slab and accelerate the corrosion of concrete and steel used in a bridge deck.

Geothermal energy, a renewable energy heat source of hydronic system, is very appealing for the snow melting and de-icing application, because it is economic and environmentally friendly. The pile foundation designed to support the loads of bridge structures can also be used as ground coupled heat exchanger. These bi-functional foundations are also called geothermal energy piles and have less initial installation costs.

In this research, a feasibility and applicability of snow melting and de-icing system using geothermal energy piles in six major cities (Toronto, Montreal, Calgary, Ottawa, Edmonton, and Winnipeg) in Canada have been studied. The energy and inlet temperature of the hydronic system required to warm up a hypothetical slab and keep its temperature above 0°C during a typical snow fall are derived based on weather condition for each city. For this purpose, a transient energy balance was used at the slab surface by considering factors such as the air temperature, snow fall rate, wind speed, and solar radiation provided for each city by Environment Canada. The coefficient of performance of heat pump is derived and the number of piles are determined for each city based on its specific local geological condition. Also, comparative economic feasibility study is performed between snow melting system for bridge decks using geothermal energy piles and electricity-based system. It is concluded that the snow melting system using geothermal energy pile is efficient and cost-effective. However, the extent of efficiency and saving varies with implementation areas.

Outcomes:

Liu H., Maghoul P., Hollaender. H, 2018. Optimum Design of a Ground-Source Hydronic Heating System of Bridge Decks during Snowfall, Physics and Chemistry of the Earth (Elsevier), In Preparation.

Liu H., Maghoul P., Bahari A., Kavgic M., 2018. Feasibility study of snow melting system using geothermal energy heat pumps in Canada, International Journal of Renewable Energy, Submitted.

Liu H., Maghoul P., Bahari A., Shahmohammadi S., 2018. Sensitivity Analysis and Optimum Design of a Ground-Source Hydronic Heating System of Bridge Decks during Snowfall, 26th Annual Conference of the Computational Fluid Dynamics Society of Canada, Winnipeg, Canada.

Liu H., Maghoul P., Bahari A., 2018. Feasibility Study of Snow Melting System using Geothermal Energy Piles in Canadian Prairies, 71th Canadian Geotechnical Conference (GeoEdmonton 2018), Edmonton, Canada.

Behavior of Concrete Geothermal Energy Piles in Cold Region

RA: Alitking Anonphouth (MSc Student) & Maryam Saaly (MSc Student)

Project Duration: 2016 – Present

Collaborators & Partnerships:

Financial Support: NSERC Discovery Grant; NSERC CREATE SERA

Project Description: 

Geothermal energy is renewable heat energy extracted and stored in the ground. Recently, to reduce additional costs of drilling and installing the conventional borehole heat exchangers and to take advantage of the fact that piles are needed to support superstructures, heat exchanger pipes are installed directly inside structural piles. These bi-functional foundations are called geothermal energy piles. This system could save up to two-thirds of the conventional heating costs in buildings. Using structural piles as ground heat exchangers is a relatively new engineering technology. The design of a thermal pile system needs to consider the local geology, groundwater, and climatic conditions. Thermal piles are subjected to both thermal and mechanical loadings, which make the interaction between the thermal piles and soil more complex. However, their behavior is still poorly understood, especially in cold regions, mainly due to the absence of reliable technical assessments and guarantees. Although the use of geothermal energy piles has been recently expanded in Canada, the adoption rate of such systems is still low in comparison to European countries and the USA.

One of the main problems facing the adoption of thermal piles in cold regions is unbalanced heating/cooling load profiles. A thermal imbalance may develop in the ground when the amount of heat extracted from the ground over the winter varies greatly from the amount of heat injected into the ground. This thermal imbalance and excessive heat extraction from the ground during the cold season can cause the ground temperature to drop below the freezing point and consequently the soil surrounding the thermal piles can freeze. Freezing at the interface between the pile structure and surrounding soil due to excessive heat extraction over the winter temporarily increases the bearing capacity of thermal piles. Once the temperature in the ground slowly rises during the spring and summer seasons, thawing occurs at the interface and the bearing capacity of such piles decreases drastically. This can lead to a system failure, adversely affect the structural integrity of such systems, and cause many problems for designers and insurance companies. Although thermal imbalance and system failure during the operation of thermal piles has been widely observed in cold regions, there is currently no established calculation method for geotechnical and energy performance design. As such, there is a pressing need for improved scientific knowledge and better-defined design procedures for geothermal energy piles.

In this study, coupled Thermo-Hydro-Mechanical (THM) numerical modeling of geothermal energy piles is performed to study the effects of thermo-mechanical loading on the bearing capacity and settlement of these piles in cold climates. This work helps to advance the state-of-the-art of this technology in Canada. A parametric study is conducted to analyze the impact of various design parameters of a thermal pile. Also, the effect of freezing-thawing cycles in the soil during the year on the functionality of thermal piles in Canadian climate has been studying. The outcomes of this research will help to develop general guidance for the geotechnical design of such systems in cold regions. New research projects are on-going to study the effect of thermal imbalance on the structural integrity of thermal piles. A new PhD student will be studying the effect of cement-based composite phase change materials on the thermal and structural integrity of energy geo-structures.

Outcomes:

Anongphouth A., Maghoul P., Alfaro M., 2019. Performance of Concrete Energy Piles in Cold Region: A Numerical Study, Canadian Geotechnical Journal, In preparation.

Saaly M., Maghoul P., 2018. Performance Analysis of a Proposed Geothermal Pile Based HVAC System for a Building in Cold Region, Building and Environment (Elsevier), In Preparation. 

Saaly M., Maghoul P., 2019. A Review on the Application of Energy Geo-structures in Cold Region, Renewable & Sustainable Energy Reviews, In Preparation.

Anongphouth A., Maghoul P., Alfaro M., 2018. Numerical Modeling of Concrete Energy Piles using a Coupled Thermo-Hydro-Mechanical Model, 71th Canadian Geotechnical Conference (GeoEdmonton 2018), Edmonton, Canada.