Graphic representation of the planned community park building. Graphic courtesy of the City of Cottage Grove
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Council discusses Glacial Valley Park building plans

The new Glacial Valley Park is in the process of being built at 9900 Ravine Parkway South. The city has made it a goal to make the park building 100% carbon neutral, utilizing solar and geothermal heating and cooling systems. While these ideas were embedded into the original $4 million budget and design plans, they still pose a significant engineering challenge, because efficiency is largely dependent on location-specific geological realities, not to mention the wide-ranging Minnesota climate.

Parks & Recreation Director Zac Dockter stated at the meeting that the city is aiming to achieve a net-zero carbon footprint with the new park building. Mayor Myron Bailey also pointed out the city’s desire to do something a little different with this structure, incorporating carbon neutrality as much as possible while using a visual design that is more “unique,” as opposed to the more traditional brick and mortar park buildings already successfully in use throughout the city.

Dockter noted that the planned solar array “will basically cover all electrical usage, and the geothermal is meant to take care of the HVAC and mechanical systems.” But in the case of failure to heat the building in frigid temperatures, a small backup boiler is planned to be incorporated to kick in at times that could arise in the event that the fuel-saving geothermal temperature control system can’t keep up. Environmentally friendly, renewable, and generally reliable, geothermal technology is expected to do its job throughout a standard Minnesota winter. However, lack of a backup heating source might potentially render the building unusable by residents during periods of extreme cold.

John McNamara of Wold Architects & Engineers, the firm tasked with the design and installation of the new system, spoke to the plans of implementing the new geothermal heating and cooling system. He described two design options: a vertical reservoir drilled 100-140 feet into the ground, or a horizontal reservoir that can be situated about 40 feet below the surface. While both are well beneath the frost line, the geology of the land where the park is being built likely contains a layer of limestone below a 100-foot depth, making vertical drilling more costly and difficult.

Below-ground temperatures get warmer the deeper you dig, and can range from 50 degrees to upper 60s, depending on the depth. Around 30 feet down, the ground temperature tends to take on the average temperature of the location, in this case about 50-55 degrees. A horizontal reservoir dug 40 feet below the surface has currently been deemed the preferred choice by the engineers for the Glacial Valley site.

Councilmember Dave Thiede raised concern of future costs and posited that if for some reason the geothermal system isn’t able to keep up, it’s possible the planned small fueled backup boiler might not be enough to properly heat the building, resulting in costly renovations that might have to be made after construction has been completed.

Councilmember Tony Khambata added that geothermal and solar will have the benefit of not being beholden to the price fluctuation of fuel and gas prices, noting more stability, the higher introductory cost notwithstanding.

After further discussion, Mayor Bailey recommended pulling the item from the standard consent agenda to discuss separately at a later time.

November 9, 2022