An inquisitive, perceptive, and innovative engineering approach by Falcon Engineering helped Royal Roads University avoid unnecessary construction costs, as well as disruptive work, in the design for a geoexchange ground coupling system for the Dogwood Auditorium.
A “geoexchange system” may sound complex, but it is really as simple as its name implies: exchanging “heat” from earth materials or groundwater below the earth’s surface with the building’s HVAC systems, so as to provide heating and cooling energy, all without consuming fossil fuels or adding to the building’s Carbon Emissions. Our blog, An Introduction To Geoexchange, gives an overview of geoexchange engineering systems.
Falcon’s Energy Engineering team has completed just such a project at the Dogwood Auditorium at Royal Roads University, near Victoria BC.
The Royal Roads Campus is situated at the base of a prominent escarpment slope. Areas on campus along the base of the slope have high water tables and, in some areas of the Royal Roads campus, footing interceptor drains are required to control shallow groundwater to protect buildings and infrastructure. Water intercepted by these drains throughout the year is collected and conveyed by pipeline as stormwater discharge. Several years ago, the campus irrigation system was outfitted to use water from the interceptor drains as the main source of water for grounds irrigation to make beneficial use of the intercepted water.
When a project arose to convert the swimming pool (originally built in the late 1950s for the former military college) to a new purpose, the Royal Roads planners wanted to ensure that reducing carbon emissions was an important component of the project plan and budget.
Royal Roads University selected Falcon’s Energy Engineering team, under a competitive RFP process, to examine the natural setting and propose a solution for an alternate energy system to be applied at the legacy building, repurposed as the Dogwood Auditorium.
The project to regenerate the building for learning and events space was opened in its new format in Spring 2021, including the geoexchange heating and cooling system. The system resulted in significantly reduced Greenhouse Gas (GHG) emissions for the Dogwood Auditorium, while providing the energy for comfort conditions throughout the year, with little reliance (peak heating) on fossil fuel energy.
Falcon was selected to design the new geoexchange ground heat exchange (GHX) system (HVAC design was already awarded to another firm), and in the summer and fall of 2019, conducted a thorough site-specific Geoexchange Suitability Assessment (GSA) to investigate the most suitable geoexchange options for the project site. The initial concept envisioned by Royal Roads University (RRU) included an open-loop water well geoexchange system, whereby groundwater would be pumped from one or more extraction wells from which the groundwater would be passed through a heat exchanger, and subsequently re-injected to the ground by one or more injection wells.
However, through the process of conducting the GSA, Falcon became aware of the presence of the significant drain water discharge. Exploratory investigations by Falcon of rushing water in manholes near the prospective Dogwood Auditorium led to the reveal of an existing, readily available energy source, already “plumbed” near the surface.
Falcon conducted further investigations and analysis to establish that the drainage water would be of sufficient flow quantity, and at a satisfactory temperature throughout a given year, before committing to the client that the drainage water would serve as a suitable and reliable ground source coupling for the geoexchange system.
Data from Environment Canada of seasonal climate norms over a period of approximately 30 years was critical to the analysis. Flow rates of the drainage water were measured over the spring and summer of 2019 and added to anecdotal information from the RRU Operators of the irrigation system. Together, these data sets were applied to a calculated “stress test” to ascertain the values of the drain water system as a source of energy to moderate indoor temperatures of the Dogwood Auditorium, as well as to ascertain the likely impacts of the “heat rejection” back into the drain water system during each of the four seasons. The combined analysis demonstrated that this drain water system could be relied upon as an appropriate energy source for heating and cooling the Dogwood Auditorium, and that heat rejection from the Dogwood Auditorium would not deleteriously affect the adjacent ocean water temperatures, to which the drain water from RRU flows.
Thus, Falcon was able to demonstrate the values of the proposed ground source coupling to the geoexchange system and was also able to demonstrate that the environmental impacts of using the ground source coupling (the drain water system) would not impose undesirable impacts (such as excessively warm temperatures) on the drain water or the ocean water.
With any type of retrofit or repurposing project, unexpected findings and conditions are prone to be discovered and this project was no exception. Although the intercepted groundwater-derived drain water had been used for many years by the irrigation system without any history of debris or sedimentation problems, new flows were recently added to the drain water system that included contributions from rooftop drainage. In many geographic locations, rooftop drainage would not pose significant problems; however, on the heavily treed RRU campus, rooftop drainage can be laden with organic debris. In this case, organic debris in the form of evergreen needles and other organics, entered the drain water system from the new sources and contributed to maintenance concerns for both the existing irrigation system and the new geoexchange system. A simple screen and diversion modification was implemented by the Project Civil Engineer in Fall 2021 and seems to be working effectively. Ongoing monitoring is warranted and perhaps additional modifications may be required.
The portion of the heating load served by ground source heat pumps for the Geoexchange System, employing energy derived from the flows of the drain water system existing on campus, results in a 98% reduction in emitted CO2e as compared to the “base case” of standard naturally aspirated boiler and standard air handling systems (commonly found in buildings of that age and utility).
Combined with the relatively low costs of drawing energy from the existing groundwater drainage system, when compared to employing a drilled well system and open or closed loop geoexchange system piping, the resultant system provided the client with:
A win for the client, a credit to the design engineers and installation contractors, and a credit to the institution (Royal Roads University) who commissioned the project.
The project to repurpose the former swimming pool at RRU into what is now known as the Dogwood Auditorium reflects the best in contemporary construction and facilities planning. As the Royal Roads University Climate Action Plan calls for significant GHG reductions by 2035, it was seen by University planners as an important aspect of the new use of this existing building that it would not add to the University’s GHG emissions, while simultaneously providing a much-needed events and learning space for the campus.
Consequently, as the geoexchange system delivers on the heating and cooling needs of the Dogwood Auditorium, it does not add CO2e liabilities for RRU, and provides modern ventilation and comfort conditions even when fully occupied by Convocation Ceremonies, University staff meetings, student study areas, and community events.
Royal Roads University and Durwest Construction set out with a vision to repurpose an aged facility and transform it into a state-of-the art auditorium. The level of innovation and commitment to sustainable transformation is a remarkable and defining feature of the redevelopment project. Re-purposing of the drain water, that would otherwise have been wasted, into an energy source seemed to mesh well within the vision of this type of transformation.
As a standard of practice at Falcon Engineering, we emphasize the importance for careful consideration of both the setting- and the building-specific features of a project, to thoroughly examine opportunities for development of a low carbon energy system. In the case of the geoexchange ground coupling at RRU Dogwood Auditorium, this standard of practice ensured that the opportunities inherent in the existing drain water system were recognized early in the investigation process, and subsequently led to an affordable and successful geoexchange system to serve the Dogwood Auditorium. Falcon Engineering feels honoured to have played a role on this team.
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To introduce this topic, let’s start oﬀ with an interesting fact: Anything with a temperature above absolute zero (-273°C) has heat energy in it. As well, anything warmer than absolute zero has stored energy. Geoexchange technology captures and uses stored heat from the ground for providing energy-efficient heating and cooling for buildings ranging from single family residential homes to the largest institutional and commercial buildings. What makes geothermal energy even more interesting, is that this isn’t new technology. The technology has existed for decades and has been improved, and adapted upon. With wise and thoughtful design adapted to specific site conditions, geoexchange systems can be cost-effective, and can be adapted for homes, commercial and institutional buildings, and industrial process applications.
Geoexchange heating and cooling (also sometimes referred to as ground source heat pump technology, or geothermal heat pump technology) is a technology option often considered as a part of electrification strategies for decarbonizing heating loads. In many applications, well-designed geoexchange systems can eliminate, or nearly eliminate, carbon emissions associated with building heating and cooling.
The geoexchange principle relies on a specific application of the refrigeration cycle for transferring heat from one place to another. By moving heat instead of converting chemical energy into heat (e.g. fossil fuel combustion), geoexchange systems can often provide space and/or process heating (and cooling) in a much more energy-efficient manner than conventional heating or cooling systems. Geoexchange heat pumps can extract energy from low-grade heat sources (at temperatures below 5°C) and “concentrate” the heat to a higher temperature for delivery to a heated environment. Hence, heat pumps can be coupled to a ground heat exchanger (often consisting of buried piping within the earth) so that the ground becomes the heat source for the system.
The energy-efficiency of a heat pump is dependent on the temperature of the source/sink that it is coupled with. In heating mode, the energy-efficiency increases as the source temperature increases. In cooling mode, the energy-efficiency increases as the rejection temperature decreases. Because the undisturbed earth temperature is warmer than the average winter air temperatures and cooler than average summer air temperatures, the ground makes for an attractive heat source for winter heating and heat sink for summer cooling.
The ground energy harnessed by geoexchange systems is renewable energy. Most of the energy captured by geoexchange is solar energy absorbed by the earth’s crust while a smaller portion is core geothermal energy. In the geologically diverse western cordillera of BC, the core geothermal component varies from site to site and in some cases anomalously high geothermal gradients may cause the core geothermal component to be significant. Although electrical energy is required to drive the heat pumps, carefully designed geoexchange systems are capable of achieving coefficients of performance (COP) exceeding 3.5 in heating mode (COP is the ratio of the total heat delivered by the heat pumps relative to the electrical energy required to drive the heat pumps). At a COP of 3.5, 71% of the total heat delivered is renewable energy transferred from the ground and the remaining 29% is derived from grid electricity. Types of
Ground heat exchangers (GHXs) can take many forms, but all forms belong to one of two broad categories:
Systems comprised of a network of vertical boreholes are the most common type of geoexchange system – but sometimes other types of systems are suited depending on site-specific setting. (Source: Natural Resources Canada)
There is a common misconception that the temperature of the soil/rock surrounding a closed-loop GHX remains constant despite the transfer of heat in and out of the ground through the GHX. As a result, there is a widely-accepted perception that geoexchange systems always operate at a consistent performance level because they supposedly tap an “unlimited availability of heat at a constant ground temperature”. Unfortunately, this perception is false and misleading and often leads to inappropriate applications of geoexchange. In fact, the ongoing thermal interaction between the heat pump system and the closed-loop GHX causes the temperature of the soils that are thermally coupled with the GHX to fluctuate. The GHX temperature varies in response to the “rate” (power) and the cumulative “quantity” (energy) of heat extracted from (or rejected into) the earth and can be quite sensitive to the relative balance of the annual heating and cooling loads. Temperature fluctuations are damped as a function of site-specific soil thermal properties and the size and configuration of the GHX. As a general rule, the better the soil thermal properties, the bigger the GHX, and the more balanced the annual heating and cooling loads, then the more stable the GHX operating temperatures.
Proper accounting for these relationships is important for selecting appropriate GHX option(s) and it is crucial for supporting effective and sustainable design of the selected option.
Closed-loop type of geoexchange systems operate most effectively when they serve both heating and cooling loads. In cooling mode, the heat is transferred into the ground causing the soils in proximity to the GHX to warm and store heat. Then in the winter cooling mode the stored heat can often be re-captured from the ground for heating purposes. In this manner the heat is essentially “recycled” from season to season, resulting in considerably less strain on the GHX, and allows the GHX to behave more as a store and less as a source of heat.
With careful design, geoexchange systems can be designed to sustainably serve one-way heavily dominant heating loads. For closed-loop type of systems, bigger GHX systems are typically required to serve one-way loads (e.g., more boreholes or deeper boreholes), and the spacing between the boreholes needs to be significantly increased so that the GHX is in thermal connection with a much greater mass of soil from which to transfer heat. For open-loop type systems serving one-way loads, greater attention to the separation between extraction and return points is required.
The cost for constructing the GHX portion of geoexchange systems varies by a factor of nearly ten-fold per unit capacity.
The large range is attributed to many factors including:
An objective evaluation of site-specific conditions and available site-specific options at an early stage in the planning process can help identify unique geoexchange opportunities (improving technical performance, reducing cost, or managing risk), and can help identify constraints or limitations that may impede suitability for geoexchange adoption.
Along with air-source heat pump systems, geoexchange heat pump systems will play a crucial and growing role in eﬀorts to decarbonize building heating and cooling. Geoexchange is particularly suited in the following scenarios:
While geoexchange heat pump systems aren’t particularly complex, they do require thoughtful and thorough design, and particular care in optimizing the integration of the geoexchange subsystems including:
1) Ground Heat Exchanger
2) Heat Pump Plant
3) Distribution System.
Heat pumps deliver heat differently than combustion systems and the design of the systems needs to take this into account. Falcon Engineering has developed a core expertise in optimizing heat pump performance based on careful monitoring of the performance of several dozen large institutional geoexchange heat pump systems we’ve designed. We’ve aggregated a lot of lessons learned expertise.
In particular cases, such as the Canyon Falls Middle School in Kelowna, our team implemented geoexchange technology to heat and cool the school. The system consists of a network of 24 boreholes drilled deep into the underlying bedrock to a depth of 600 feet. Along with geoexchange, the school was equipped with solar PV panels, LED lighting, occupancy based controls, and a network automation system to reduce the energy use intensity of the school.
The net result is a near elimination of carbon emissions relating to the operation of this school. In this case, Falcon Engineering Ltd. provided mechanical, electrical, and energy system engineering services including energy modelling and geoexchange system design.
As a leader in green, energy eﬃcient building systems, Falcon Engineering is well-suited to identify and implement low carbon energy solutions, including geoexchange where it is suitable, or identify other suitable low carbon alternatives for speciﬁc buildings in speciﬁc settings. At Falcon Engineering, our clients demand low carbon energy strategies to help guide their decision-making today, for achieving compatibility with tomorrow’s expectations. Reach out to us to speak with our highly qualiﬁed team of engineers, scientists and technical analysts about your geoexchange needs.
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