BIG SKY, MONT. — For Marc Montanus and his wife, geothermal was ideal when deciding what type of HVAC system would be most efficient for their new, radiant heated mountain home in Big Sky, Mont. The couple elected to design and install a geothermal system for two simple reasons: efficiency and cost.

“By taking advantage of the earth's heat, we can reduce the energy required to heat our home and that's a good thing,’ said Montanus. “Because this home is not our year around residence, we were also focused on keeping our annual expenses as low as possible.  The opportunity to reduce our propane bills was too attractive not to consider. Plus, our home is constructed with reclaimed materials and using an energy-efficient geothermal system helped continue that theme of low environmental impact.” 

Montanus was first introduced to geothermal as a heating option by the project’s architect and owner’s rep. They also introduced him to Energy 1, a design-build and consulting firm located in Bozeman, Mont., early in the design process. By discussing the different systems available with Energy 1, Montanus learned firsthand that a geothermal system is an investment, first and foremost.

“It costs more up front, but over time you'll save money on your heating bills and that's the return on investment,” explained Montanus. “A lot of people probably focus on the initial cost, which is understandable, but if you are able and prepared to take a longer term view, this system makes a lot of sense. We were fortunate because at the time we installed our system the government was offering tax incentives [these incentives are still available] that really helped the numbers.”

Initial projections

As homeowners, Montanus and his wife were intimately involved in the design of the home. Working early on with Energy 1 allowed Montanus to learn about having a geothermal heating system, such as what it entails, how much space it will take up, maintenance of the system, etc.

“We did an introduction for Marc, showing a traditional system versus a geothermal system,” said Leo Crane, project manager and vice president at Energy 1. “We showed them the estimated ROI and the net cost difference between the two systems, and we walked through each option from a comfort and control standpoint. We went over the ground source option, what the projected reduction in propane usage and maintenance costs were.”

Once the owners decided on the geothermal system, Energy 1 created an energy model, based on the overall architectural building design, building location and orientation, owner occupancy and usage patterns, heating set points, finished floor types, mechanical equipment specifications, building envelope details, lighting system, on-site geologic conditions and weather patterns of the last five years. 

“When we modeled this we were looking for propane savings of 60%-70% overall,” said Mike Foran, senior project manager and president of Energy 1. “At the time, the assumed cost for heating the home [with a traditional non-geothermal option] for one year was $7,428.57, based on the cost of propane and electricity then,” said Foran. “When looking at propane costs per year now with the geothermal system, heating the home for one year is just over $1,000, thus, the approximate reduction is 85%.” 

“Typically we like to keep things conservative when doing an energy model,” added Crane. “And Marc’s information on propane purchased since the home was built indicates our initial results were in fact conservative and that we were exceeding what the projected propane reduction would be.”

According to Foran and Crane, the ROI on this system is four years based on current propane and electrical rates.

Energy 1 also oversaw the design and installation of the radiant flooring in which Uponor/Wirsbo PEX tubing was installed. At first, the homeowners wanted five to six radiant zones throughout the house.

“Once they started to explain when and how they were going to occupy the home, we dove into it more, to better manage occupant comfort and climate control, as well as overall system efficiency” explained Crane. “We ended up adding to the zones, to a total of 10.”

The home was completed and turned over to the homeowners in the winter of 2010. Montanus has family that stays at home on a regular basis, and there is also a care taker.

Project coordination

Energy 1 oversaw coordination of the different trades working on the project.  

“We provided a schedule and on-site coordination to ensure successful integration of select trades — from design to installation to commissioning to close out,” said Crane. 

There was also a record snowfall that added to the schedule and coordination of the project.

“In terms of the overall project, snow at this location (and at this elevation) always has an effect on the project,” said Crane. “For the bore hole drilling, snow fall and weather was certainly taken into account in order to have the most favorable site conditions as possible to develop the boring field in a timely manner. Also, the bore hole drilling was very closely coordinated with the general contractor, so as to not affect their day-to-day progress and access in/around the site.” 

Drilling was done by Bertram Drilling Inc., based in Billings, Mont. Eight vertical bore holes, 200 feet deep each, were drilled and ¾-in. loops were installed into each bore hole and backfilled with a standard bentonite grout slurry. The drilling process took approximately three days.

The architect, Pearson Design Group Inc., and general contractor, Lohss Construction Inc., both based in Bozeman, Mont., also worked closely with Energy 1.  

“Energy 1 worked within the architect’s parameters, which was certainly an opportunity to get really creative,” said Crane. “As the project developed, the design morphed and things changed, but working with the architect we were able to successfully integrate those changes and keep things fluid. Energy 1’s unique relationship with the architect allows for successful mechanical system integration within great architecturally designed spaces, both important elements all too often not mutually achieved on projects.” 

For example, the mechanical room size and layout was reduced as a result of a wine room being added to the design of the home’s interior. The mechanical room, which houses a GeoComfort water-to-water unit and Lochinvar boiler that is used as a backup, is under a stairwell, across from the laundry room and adjacent to the wine room.

“The wine room eventually overtook a good portion of the area originally designated for the mechanical room,” said Crane. “The placement of the mechanical room also had the potential to introduce acoustical issues. However, with strategic equipment selection and placement and acoustical treatments to the actual equipment in the form of vibration isolators, noise reducing neoprene pads and acoustical treatments to the actual mechanical room envelope — we completely avoided what could have been detrimental acoustical issues.”

Post-occupancy monitoring

Energy 1 provided post-occupancy monitoring and temperature logged each radiant zone, including time of day of test and outdoor temperature readings at the specific time of each testing.

“We tested numerous times, at varied times of the day, to make sure the testing and our analysis was inclusive of all potential (and varying) conditions,” said Foran. “The purpose was to test/confirm basic operation of the system and overall that it was operating as comfortably and efficiently as possible (ie: verify set points were being achieved and arriving at such set points within a specific window of time, etc.).”

Energy 1 advised Montanus to target a thermostat setting of 50°F-55°F while they were planning to be away for extended periods of time, and the garage to 45°F-50°F year-round. 

“Approximately two days before arriving to their residence, we instructed them to arrange to have the temperature raised back up to their preferred settings, allowing the house ample time to most efficiently come back to the desired ‘building occupied’ settings,” said Crane. “Minor operational-type details, but in the overall picture, can equate to sizable savings in heating costs.”