RiverWalk at Loon Mountain: Brilliant Engineering Adds Energy Efficiency To Luxurious Living
Posted on November 10, 2016
Seated directly across from Loon Mountain’s South Peak Expansion, RiverWalk—a seven story condominium hotel in Lincoln, New Hampshire—offers a luxurious gateway to the region’s vibrant beauty and multi-season recreational activities. But the same location so rich in aesthetic rewards presents formidable energy challenges. With full frontal exposure to the sun and a mountain at its back, RiverWalk demands heat and AC simultaneously during the shoulder seasons that occupy most of the year.
Yet RiverWalk has turned the challenge into an opportunity. At the core of its heating design, 214 vertical water-source heat pumps serve the 84 available units. Acting independently, the heat pumps can deliver AC to units facing the sun, while heating others in the shade. Wayne Fillion, president of Yeaton Associates, the engineering firm that collaborated with general contractor Dan Hebert, Inc., explains the virtues of the system. “Each heat pump has its own compressor,” he days. “You can have parts of the building in a heating load while others are in a cooling load; some units produce heat, while others absorb it. They share a common water loop that balances the load most of the year, so we don’t have to run the boilers and cooling towers unnecessarily.”
Viessmann technology critical to successful execution
In principle, RiverWalk’s “balanced load” approach is relatively straight-forward. But the scope and complexity of the luxury property make successful execution challenging. George Hebert, Dan Hebert, Inc.’s lead supervisor (but not a family relation), outlines the system. In addition to the 84 units that must be heated and cooled, RiverWalk includes “twelve, 119 gallon horizontal indirect tanks for domestic hot water, eleven cabinet heaters for stairways and entry ways, five linear feet of sidewalk snow melt, and four 600,000 BTU heat exchangers serving two hot tubs and two heated pools.”
In addition, peak winter demand requires more heat than the heat pumps can provide. “The cold return goes to our boiler room,” George Hebert says, “where a two-way modulating zone valve mixes water from the supporting boilers.”
Given the need for supporting heat, plus additional loads, RiverWalk needed boilers and heat exchangers that could deliver efficiency and flexibility. “The boiler plan includes much more than a heating loop,” says Fillion. “We have DHW, snow melt, pools and cabinet heaters. As a system, we need both low-temperature and high-temperature water; we chose Viessmann because it’s capable of producing a wide range of temperatures under various loads.”
Ultimately, RiverWalk installed four Vitocrossal 200 CM2 620 high-mass condensing boilers, each producing 2.2 million BTUs. These units share the boiler room with the twelve indirect hot water tanks. “We really like the boilers—they’re really energy efficient,” says Dan Hebert, president of Dan Hebert, Inc. “Because they’re condensing boilers, they produce a low-temperature exhaust—we were able to vent them outdoors without building chimneys or stacks. The condensers are stainless steel, built for longevity. And Viessmann has great technicians who came out to help set everything up.”
The four Vitocrossal 200 CM2 boilers are cascaded via Viessmann controls, and piped reverse-return to balance the load and ensure longevity. Four 1,000 gallon propane tanks, stored underground, provide the fuel. To maximize efficiency, the system is designed around a target water temperature of 140° F. By designing the system with large coil emitters in each living unit, RiverWalk can sustain a low loop temperature and ensure return water temperatures cool enough to facilitate condensing, an essential key for energy efficiency.
The Viessmann heat exchangers for DHW and the heated pools apply the same physical principles. “It’s important to note that Viessmann’s engineered DHW plan is a tidy package capable of meeting substantial demand,” says Fillion. “Their heat exchanger technology transfers a maximum amount of heat in a relatively small volume.”
RiverWalk is a work in progress that began construction approximately two years ago. With the completion of Phase II in the late spring, RiverWalk launched the grand opening of its 84 residential units on June 24, 2016.
RiverWalk at a glance:
- 84 condo units with luxurious hotel accommodations
- 2 heated pools
- 2 hot tubs
- 214 vertical water heat pumps
- 4 Vitocrossal 200 CM2 620 2.2M BTU high-mass condensing boilers
- 12 119 gallon indirect DHW tanks
- 4 600,000K BTU heat exchangers
- 4 in-ground 1,000 gallon propane tanks