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Digging into ground source heat pump potential in Minnesota

Northwest, MN

A handful of folks from Northwest Minnesota recently welcomed Ed Lohrenz of GEOptimize to share his insights on siting ground source heat pump or geoexchange systems. Ed focused on the most important elements to consider in system design and current industry trends.

Shannon Stassen, Northwest CERT Coordinator, connected with Ed at the suggestion of our colleagues at Otter Tail Power Company who have worked with Ed on several projects.

Ed kicked off the session by sharing two key acronyms: GSHP system = Ground source heat pump. GHX = ground-coupled heat exchanger.

Seven elements to consider in system design

  1. Look at the whole building—or district—as a system.
  2. Rather than relying on “standard assumptions” you really want to do a detailed assessment: heat loss and heat gain calculations for every hour of the year so you know how much to heat and how much to cool. 
  3. Need to consider occupancy. 
  4. Need to think about the heat from the compressors that run the heat pump because it may amplify the cooling needs or diminish the heating need. 
  5. Projects can take on different flavors–some are heating dominant and others are cooling dominant.
  6. Best to be connected with the system design team and system owner because all of the details matter, including what glass is being used for the windows, how much ventilation the building needs, etc.
  7. The geology matters (e.g., clay is more limiting in terms of how much heat it will absorb) as does the land area available for the loop field (e.g., spacing between loops or boreholes matters). 

Project example: Perham High School

Project example: Fergus Falls Library

Five ground source heat pump industry trends

  1. Partner early on design to reduce system cost. System design is central to this! Ed said they can often reduce the cost of the system by 35%-65% if they are able to work with the architect and mechanical system designer at the outset of the building design.
  2. Techniques are evolving. Horizontal loops or horizontal drilling can be less expensive and more effective than deep loops. In addition, some places are now installing them in tunnels (roads, subways) rather than drilling, or in water mains and shallow aquifers.
  3. Dig into the details for feasibility. GeoFease–a tool they are developing with Otter Tail Power Company–provides a way to develop better feasibility estimates that go deeper than “standard assumptions.” The tool includes a number of different building types, along with square footage, alternative fuel types, and efficiency measures (including changing glass specifications, exhaust air heat exchangers, recognition of domestic hot water loads, for example) that all help get better, closer screens of the potential for appropriately sizing and designing a ground source heat pump system. 
  4. Use an energy meter to track performance and adjust usage accordingly. Ed shared an example: an IKEA in Denver where this allows them to dissipate some heat for snow melt; an ice rink with a pool next door that then dumps excess heat into the pool; and a building in Perham that can change the tint of the glass in the building to change how much heat they are trying to expel. These designs can also really lower first cost, improve system efficiency and ensure long-term performance by allowing a system to avoid adding too much or pulling too much heat over the life of the system.
  5. District geothermal–or energy sharing–is growing. The energy load profiles of different buildings–like an office building and an apartment building–have complimentary loads. When all buildings are connected to one single pipe, it’s like being on a conveyor belt to move the heat. It works particularly well when there are a diverse mix of use cases in buildings. For example, like with college campuses, the combination of residential facilities, office facilities, teaching facilities and maybe also an ice rink and pool, is a good mix. One can reduce the size of system by 10% or more than it would need on its own. AND, it can be expanded in a modular way. This allows for lower capital costs, and also allows a user to take advantage of natural equipment retirement cycles.

Watch the event recording

Please download Ed’s full presentation or watch the event recording if you'd like to learn more. Here are a handful of other interesting updates:

Ed's presentation
Download
Otter Tail rebates
Download

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