NREL enhances REopt web tool

Geothermal heat pumps use underground temperatures as a thermal reservoir that enables efficient heating and cooling. REopt’s new feature evaluates vertical bore heat exchangers combined with auxiliary heat exchange units, which reduce the number of boreholes required for a GHP system. Illustration by NREL, adapted from DOE’s Geothermal Heat Pumps website

The publicly available REopt web tool is a techno-economic decision support platform used to optimize energy systems for buildings, campuses, and microgrids. REopt identifies the optimal mix of renewable energy, conventional generation, energy storage, and now GHP technologies to meet cost savings, clean energy, and resilience goals.

GHP retrofits often require renovation to a facility’s heating and cooling systems. While retrofits can improve heating and cooling efficiency and reduce associated carbon emissions, justifying GHP retrofits based on building economics alone is sometimes challenging. NREL researchers have added another GHP configuration option to REopt to help analysts identify cost-effective solutions. Hybrid geothermal heat exchange (GHX) technology integrates GHP systems with auxiliary heat exchange units, allowing facility owners and managers to reduce GHX system capital costs while improving the overall economics of GHP projects.

To demonstrate the potential benefits of hybrid GHX, NREL conducted a case study using the REopt web tool. The study compared a non-hybrid GHP system to a hybrid GHX system in a large office building in Las Vegas, Nevada, with a total area of 498,588 square feet. The analysis considered electricity costs of $0.10/kWh energy charges plus $10/kW monthly demand charges and natural gas costs of $10/MMBtu. The study results revealed significant cost savings and improved performance with the hybrid GHX system. The non-hybrid GHX system required 310 boreholes, each 400 feet deep, while the hybrid GHX system needed 56 boreholes plus an auxiliary cooling tower with a capacity of 245 tons.

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