phc april 2011
www.phcnews.com
GREEN SYSTEMS
was struck with a strong feeling of deja vu. As it turns out, I had designed this solar heating retrofit myself back in 1987 and had worked as one of the installers that put it together that summer. If this heating system had been an automobile, it would
have been designated a “classic car” and given special license plates. It is nearly 25 years old and still runs. In fact, the original owner still depends on it to control his heating bills. A new backup boiler had just been installed, along with some other new heating components, and the owner just wanted to upgrade the controls to handle the new equipment. The system is presently back in service. Before the solar retrofit in 1987, we walked into a house
where construction had recently been completed, including hydronic radiant heat downstairs with plastic tubing embedding in concrete mass floors. A conventional “hot water” electric boiler provided heat to the floors, using a single Grundfos circulator (UP26-96) and some zone valves. The warm mass floors added up to just under 2,000 square feet. The retrofit included six 4
5 8 collectors mounted on the ground next to the house. The south-facing slope of the terrain allowed us to screen the collectors from view with existing trees. See Figure 33- 1 for a view of the collectors as they look today. They appear in the trees to the left of the wooden “coyote” fence just below the house. Single-minded design goal This solar heating retrofit
was not intended to be a combisystem. The original intention for these solar collectors was simple: to provide baseline winter heat for the mass floors. The owner wanted enough solar heat to temper the warm floors without using the electric boiler all the time and also wanted to divert unused solar heat to a spa when the heating season was over. The owner also wanted the retrofit to be as simple as possible, using the minimum
e Circle 43 on reader reply card
SOLAR SOLUTIONS A
Overheat-cooling with thermosyphon loop
BY BRISTOL STICKNEY CONTRIBUTING WRITER
few months ago, I went on a service call to evaluate an old solar heating system at a house near Santa Fe. As we approached the house in our service truck, I
equipment and simple controls. We accomplished this by
attaching the boiler, heat tubing and solar collectors together in a “solar direct” configuration, where a glycol mixture is circulated through all the heating equipment. The glycol is contained in a closed system under normal hydronic boiler pressure (typically greater than12 psi cold and less than 25 psi hot) and circulated directly from the collectors to the boiler and into the tubing in the floors. There are no heat exchangers in the system other than the plastic tubing in the concrete. The plastic is protected from solar overheating by using a thermal mixing valve.
e Turn to STICKNEY on p 68
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