Solar Thermal/Condensing Boiler Project Addresses Multiple Loads, Earns Energy Offset

In Eagle County, Colorado, local authorities not only promote energy sustainability, but insist on it. Any residential project that incorporates more than 200 square feet of snow melt, for example, must mitigate the load with an offset the draws upon a renewable energy source

For Mustafa Aydin, president of American Plumbing Heating & Solar in Edwards, Colorado, the county’s demand represented an opportunity for innovative energy planning. His client was gutting and rehabilitating a 7,000 square foot home in the Red Sky neighborhood of Edwards, completely redesigning its infrastructure to include radiant floor heating, 3,000 square feet of outdoor snow melt, improved domestic hot water, and the comfort of a heated, year-round 1,500-gallon hot tub. Before Aydin had consolidated his design options, he knew immediately where he would source the core components: “I’m a Viessmann installer and have been for many years, I won’t install anything else. They’re like the Ferrari of energy equipment.”

For design support, Aydin turned to Eric Anderson, a hydronics technical support specialist at
Ferguson Hydronics in Denver. His challenge? Create a system that would integrate solar thermal - the renewable energy resource - with condensing boilers to serve all four loads seamlessly and efficiently.

“At the highest level, we thought of the solar thermal contribution in two tiers,” says Anderson. “Its top priorities would be serving domestic hot water needs and the hot tub; at the secondary level, it would support the condensing boilers with the radiant heating and snow melt loads.”

“When you have an involved project like this,” Anderson explains, “you start with a heat loss
study to assess the loads. How much DHW do they use or need? What’s the load from the outdoor spa? Anderson ran a TSOL, a solar thermal computer simulation program that analyzes load within the context of the location’s climate and weather. The resulting analysis formed the basis for design that includes nine, 4’ x 8’ solar panels on the roof, and two Vitodens 200 wall-mounted condensing boilers. The solar system ties into two 120-gallon single-coil stainless steel tanks—one for DHW, the other to preheat water for the boilers (reducing their load)—a plate heat exchanger for the outdoor spa’s hot tub, and a 650-gallon stainless steel atmospheric tank that serves as a buffer for the solar thermal system, and as a contributing source of energy for the radiant heat and snow melt loads.

“As a contractor,” Anderson notes, “I like sticking with one or two manufacturers for consistency of parts and compatibility throughout the system.” In addition to supplying the panels, boilers, and tanks, Viessmann provided the panel line set and the boiler controls. The line set—prefabricated from stainless steel and pre-insulated—include sensor lines in the insulation for easy integration into the controls, and, says Anderson, “really solid, high-temperature O-ring connections for the panels, which means there’s need for us to do soldering on the roof.”

Cascaded for maximum efficiency

A carefully planned mechanical room manages the flow of water, and allocation of energy,
between the solar and boiler sources, using an integrated array of three-way valves and the intelligent application of the boilers’ controls. “We have the controller set for a cascading strategy that encourages the maximum amount of condensing,” says Anderson. The lead boiler usually fires at 25% to 30% of its peak modulation; when it exceeds 40% - 50%, the second boiler kicks in and the two modulate down again. “The whole goal,” Anderson says, “is to fire at the lowest rate for highest efficiency.”

While the system is complex, sourcing components from Viessmann made the project easier. “It’s the only boiler system I spec,” Anderson says. “Whether it’s solar, controls or boilers, everything’s thought out as a system. For me, that means peace of mind.”

Mustafa Aydin added, “I like to add a personal touch when finishing a project like this.  In this case, the homeowner is a Harley Davidson fan, so we added the motorcycle image to the floor.  It was a surprise gift for the homeowner and he loved it!”

Photo credit: Bill Willins Architectural Photo