What appears to be a single-family residence is actually a university’s “recycled” live-in classroom and center for sustainability education. A 119-gal, 130,000-Btuh solar water heater played a key role in the building’s sustainable radiant heating design.


 “Do what we say and what we do!” might well be the mantra for the Campus Center for Appropriate Technology (CCAT) at Humboldt State University (HSU) in Arcata, CA. When CCAT decided to remodel its live-in demonstration home and educational center for technology and resource conservation, it was done with an eye to sustainability.

CCAT, an authority on sustainable building for more than 30 years, knew that the move provided the perfect opportunity to add green amenities to the home. To get the project started, the one-story, 1920s-era home, was lifted from its site and “recycled” by moving it down the road to a new foundation. Early on, the CCAT committee decided to use radiant in-floor heating and had PEX (cross-linked polyethylene) tubing installed in the newly poured basement slab. This tubing, manufactured by Uponor Inc., would eventually carry warm water from a yet-to-be-determined heating source to warm the slab as well as the people and environs above.

Next, CCAT called in a local expert Stephen Bohner, who co-owns Alchemy Construction Incorporated, also of Arcata, to help decide exactly how to heat the lecture-library room in the basement and the upper level, which would provide living quarters for the director of CCAT and the HSU students who live and work there.

Soon thereafter, Bohner recommended the Phoenix Solar 119-gal, 130,000 Btuh water heater as a perfect fit with CCAT’s sustainable mission. Manufactured by Heat Transfer Products, the Phoenix combines domestic hot-water storage (from a solar collector panel) with a 97%-efficient, gas-fired backup - all in one unit. The sealed-combustion, direct-vent Phoenix Solar delivers both high-efficiency space heating and domestic hot water, using state-of-the-art condensing boiler technology and a modulating, load-matching gas burner.

The Phoenix Solar would feed both the 1,550-sq ft basement with its radiant floor heating, as well as the radiators that would heat another 1,550 sq ft upstairs. In addition, the unit would also provide domestic hot water for the entire house.

How The System Works

A firm believer in closed-loop systems, Bohner separated the Phoenix Solar’s auxiliary heating port for the domestic hot water from the space heating system via a Taco X-Pump Block, a heat exchanger that is also an all-in-one unit.

The auxiliary ports of the Phoenix Solar feed domestic hot water to the X-Pump Block. Using its internal heat exchanger, two pumps and control logic, the X-Pump Block relies on an outdoor reset to control the amount of hot water sent to the radiant tubing loops. Bohner explained how the system works, “We monitor indoor temperatures by running thermostat wire to each room in the house. We monitor outdoor temperatures with an outdoor sensor on the north side of its exterior. When there is a call for heat, the X-Pump Block mixes and delivers the correct water temperature - based on the outside temperature - to the radiant manifold.”

Individual room zoning is accomplished at the radiant manifold via thermal actuators, also made by Uponor. “When a zone calls for heat,” Bohner said, “those actuators pop their heads and warm water flows through the PEX loops attached to them. Again, the colder it is outside, the warmer the water delivered to the room needing heat.”

Finally, Bohner chose another all-in-one unit, the Oventrop Regusol EL-130 solar pumping station, to move water from the solar collectors to the radiant loops whenever that water is hotter than the water inside the Phoenix Solar. “Linking the Taco X-Pump Block and Oventrop EL-130 with the new Phoenix Solar was a great way for us to easily integrate a solar thermal system into the newly remodeled CCAT.”

Living Classroom

To date, the three student-residents, having never run out of hot water, are very happy with the new system. CCAT offers university students and the general public tours, workshops, and opportunities for hands-on involvement. They don’t just preach sustainable products; they actually live with them to discover whether or not they like them. CCAT provides classes on solar thermal, solar electric, and now - with the move and the renovation - radiant floor heating. “It is like a live-in classroom for sustainability,” said Bohner.

“CCAT is preaching sustainability, so they liked the idea of the Phoenix Solar because it would allow them to actually ‘walk the walk, as well as talk the talk.’” ES