A leading solar integrator in the San Luis Valley of southern Colorado, Solar Gain Services has been offering solar thermal and photovoltaics to commercial and residential clients since 2007.
When co-owner Luke Christy—NABCEP certified as both a solar heating installer and as a PV installation professional—received a call from a homeowner in Sagauche, Colo., to reduce the overall energy usage footprint as low as reasonably possible, he had the tools and pedigree to meet the energy challenge. The 2,000-sq.-ft. home was built to LEED Gold standards, is heavily insulated, incorporates passive solar features, and has a grid-tied solar electric system to help offset the electrical energy consumption.
The solution, after taking into account available budgets and the highly efficient home, was to install a hybrid combi-system—for domestic hot water (DHW) and radiant floor heat—with a large amount of thermal storage. A copper single pass tube coiled within the tank serves as the primary means of heating DHW. Since the tank is purposely stratified, with the top of the tank always being charged first. “This technique works very well,” says Christy. A setpoint control activates a Caleffi 3-way valve to divert water from the single-pass through the tankless heater when the tank temperature is low.
Eight installed Viessmann Vitosol 100 solar collectors heat a 700-gallon custom stainless steel tank through a brazed plate heat exchanger, and Christy opted to go without a mod-con boiler for back-up heat to reduce costs. Instead, a gas-fired tankless water heater paired with a plate heat exchanger and some control logic serves as a back-up heat source.
A Caleffi iSolar BX solar controller charges the storage tank in two vertical stages to ensure that the top of the tank is always as hot as possible, even in winter. This helps preheat DHW through a single-pass copper coil heat exchanger, and in practice the thermal system is able to supply solar heated DHW for most of the year without any assistance from the gas water heater. “A Caleffi BX differential controller was selected because of its ability to charge the tank in upper and lower stages. This is accomplished via a Caleffi 3-way valve that diverts the flow to the tank from the water side of the heat exchanger. This helps the upper stage stay hotter at times of low solar harvest,” says Christy.
The radiant floor distribution system extracts heat from the storage tank until a low temperature setpoint is reached, at which point the gas-fired backup is enabled. “We have used Caleffi products since 2007, when they were introduced to us by Low Energy Systems in Denver. As a system designer I appreciate the extremely high level of quality of the products, as well as the comprehensive range of products available,” says Christy.
In addition to the solar controller, Christy relied on Caleffi components throughout the install, including four Caleffi thermostatic operator zone valves, an air separator, a backflow preventer and pressure reducing valve, a balancing valve, two thermostatic mixing valves, two 3-way zone valves, flowmeter, eight sweat union connectors—used for making plate heat exchanger connections—and a small automatic air vent. In fact, the radiant loop extracts heat from the storage through a second plate heat exchanger, and delivers it to the radiant slab through an assortment of Caleffi products — a thermostatic mixing valve, a balancing valve, a bypass valve and zone valves.
One challenge in particular was the lack of a proper mechanical space for the system piping and components. Once the solar storage tank was in place, Christy realized that the space could be sheathed in plywood and used as a substrate for mounting components. However, we ended up needing all the available area of the tank exterior, which resulted in the system completely covering and wrapping around the tank.
Another challenge was the homeowners desire for solar collectors in a specific place, which was about 150’ away from the mechanical area. This resulted in a very long pipeline to and from the collectors, with potential flow and heat loss issues. These issues were resolved by using oversized and heavily insulated underground piping, as well as a larger collector loop pump.
Customer ‘Pipes’ In
This system has just gone through its third winter of operation and has been an outstanding success, with a glowing report from the homeowners and zero service calls. The homeowners report that they are comfortable all year round and only refill their 250-gallon propane tank once a year. The single tank supplies all the fuel for the heating and DHW backup, as well as a gas range and a gas fired clothes dryer, so the savings would seem to be significant. On future installations of this kind we will be installing a web-connected energy meter, which will enable us to collect enough system data to translate the daily energy harvest into the corresponding economic benefits.
“The homeowners have had nothing but good things to say about the system. We did not have a single callback on the system until a severe windstorm damaged some collector mounting hardware three years after the system was commissioned. When we checked system operation at that point, everything was still performing properly, with no leaks or control glitches,” says Christy.
According to Christy, Callefi’s commitment to innovation and constant improvement is extremely important, as is their commitment to education and training. The Coffee with Caleffi webinar series and their Idronics publications are a really valuable resource for the hydronics professional constantly looking to hone his/her skills.