Doing it Right
Although today's renewable energy policies often focus on electricity generation and biofuels for transportation, up to 40-50% of the total global energy demand is for heating and cooling. Ground-sour...
Although today’s renewable energy policies often focus on electricity generation and biofuels for transportation, up to 40-50% of the total global energy demand is for heating and cooling. Ground-source heating and cooling (GSHC) systems are a versatile, proven technology with low carbon emissions for applications ranging from small residential buildings to large commercial and institutional developments. GSHC is a great unsung technology.
David MacKay, chief scientific advisor to the U.K. Department of Energy and Climate Change, is a big GSHC fan. He asks: “Can we reduce the energy we consume for heating? Yes. Can we get off fossil fuels at the same time? Yes…[W]e should replace all our fossil-fuel heaters with electric-powered heat pumps; we can reduce the energy required to 25% of today’s levels…Heat pumps are future-proof, allowing us to heat buildings efficiently with electricity from any source.” 1
With their first patent dating back to 1912, GSHC systems have been used for many years. But as the demand for renewable energy production rises, they have been growing in popularity. According to the Canadian GeoExchange Coalicontinued tion, over 15,000 new units were installed across the country in 2008, about 3.5 times the number just two years earlier.
As the market for GHSC explodes, the hydrogeological and planning impacts of these systems must be addressed. We must ensure that the natural earth energy resource is used fairly and sustainably.
Hidden below the ground
GSHC systems consist of a subsurface loop, a heat pump and a distribution system. Open-loop systems draw water from two or more wells and return it after use to the aquifer or a surface water body. Closed-loop systems use pipes buried in the ground horizontally, vertically, or in a coiled configuration. Within the loop an antifreeze-water solution is continuously circulated.
Despite their benefits, GSHC systems can pose some concerns regarding their impact on the host terrain. There is concern, for example, about the following:
• Potential leakage from the GSHC system of heat transfer fluids (for closed-loops) or water geochemical changes.
• Thermal pollution if the subsurface becomes hotter or colder than the ambient conditions. This heat or cold could travel in the subsurface and affect adjacent properties or systems, surface water bodies or flora/fauna.
• Well biofouling or clogging from subsurface biological changes.
• Preferential flow pathways (ways for contaminants more easily to reach the subsurface) due to improper siting, maintenance, and decommissioning of the GSHP system.
• Groundwater flow rate reductions from exces- sive chilling or ground freezing.
• Aquifer depressurization in areas with artesian conditions, or water table mounding from water discharge.
• Frost heave, swelling, or ground subsidence. We do not know as much as we should about these potential issues. More technical study that couples long-term field monitoring data (temperature and water biogeochemistry) and numerical modeling are required.
There is little GSHC legislation across the world. According to British hydro and thermogeologist David Banks, “In many areas of ground source heat technology, there is currently a ‘regulatory vacuum’ — laws simply do not exist in many countries to govern the use and abuse of the subsurface heat resource. In the absence of binding legislation, regulators and professional trade organizations are seeking to develop codes of best practice.” 2
Some of the most detailed regulations have been developed in Germany, Sweden, and Austria. In Canada, minimum requirements, including site selection, equipment and materials, design and installation, testing and decommissioning, have been recommended by the Canadian Standards Association (C448). The standards are embedded in the Ontario Building Code, for example.
For commercial systems, the CSA standards advocate that professional engineers do the design, and that professional geoscientists investigate the groundwater/subsurface conditions. In British Columbia, a code of practice for well construction, testing and maintenance in the Ground Water Protection Regulation under the Water Act includes provisions for open and closed-loop systems. Although standards and water resource-related legislation exist, there is no comprehensive legislation dealing specifically with hydrogeological aspects of GSHC installations across Canada.
In order to protect our water resources, dependent ecosystems, consumers and the GSHC industry, the regulations for subsurface development and community planning must be updated to reflect the rapidly growing GSHC industry. In Ontario, for example, the Ministry of the Environment has recently undertaken a consultation process to determine if policy or regulation changes are required. Standards surrounding system siting (including reporting), maintenance, and decommissioning are essential. Watershed-scale protocols must be developed for conservation authorities. Technical hydrogeological research must be applied to develop policy for such issues as the appropriate system densities in different geological settings.
According to environmental engineer Paul Younger, GSHC sustainability requires three things: financial viability; social limits to ensure the use of the natural resource by others is not compromised; and protection of natural ecosystems. These broad and comprehensive principles must form the basis of GSHC planning policies. 3
GSHC systems cannot be installed haphazardly without incorporating hydrogeological and planning considerations. Community planning and district energy heating and cooling schemes must ensure the equitable and sustainable use of this technology. Engineering research, regulations and guidelines must grow with the industry.
There must be an informed, evidence-based balance between over-prescriptive regulations that can hamper the industry in the immediate future, and the need to guarantee the long-term sustainable use of these systems. Canadian consulting engineers and geoscientists have an important role to play in this undertaking.
1 MacKay, D., Sustainable Energy– Without the Hot Air. 2009, UIT Cambridge, England, p. 153.
2 Banks, D., An Introduction to Thermogeology: Ground Source Heating and Cooling. 2008, Blackwell, Oxford, England, p. 273.
3 Younger, P., Ground-Coupled Heating-Cooling Systems in Urban Areas: How Sustainable Are They? 2008, Bulletin of Science, Technology & Society, 28(2), pp. 174-182.
Jana Levison, Ph. D., EIT is with the Ontario Centre for Engineering and Public Policy (OCEPP) in Toronto.