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Solar Solutions Continued from page 26


on this job. (Remember that this equipment has been out in the weather for almost 25 years, so it is not showroom new.) When the pumped circulation in the collector stops, the hot fluid in the collector tends to rise to the top head- er. A tee connection at the outlet pipe (Fig.33-2, upper left) connects to cooling fins mounted on the back of the col- lector (Fig.33-2, center) that contain cool antifreeze, which is heavier than the hot antifreeze and tends to “fall” downhill. A tee connection at the collector inlet allows the cold fluid to slide downhill into the bottom of the collec- tor as hot fluid rises up and out the tee at the top. This thermosyphoning continues as long as the sun pro-


vides heat, or until the circulation pump turns back on. When the pump is on, the cooling loop snaps shut, using


Figure 33-2


tanks. The large volume of glycol required to fill the floor tub-


ing seems to contribute to the longevity of the glycol. The original Grundfos circulator was still there and still running. Do Over: The thermosyphon cooling would probably work better


with larger diameter tubing. Upsize the ¾ inch supplies and tees to 1". The thermosyphon cooling would work even better


with twice as many ¾" fin tubes placed in parallel for low resistance to flow. Larger diameter fin tubes are also a good alternative and available commercially. The owner of this system willingly tended to some


minor seasonal adjustments. We no longer design systems that require manual intervention such as collector covers or seasonal valves and switches. The success of a heating system should not be personality dependent. Only high temperature pipe insulation withstood the


test of time at this job. The only solar pipe insulation that survived for the duration out in the weather was the stuff covered by metal foil.


a passive check valve (located near the bottom inlet tee) that closes in response to the relatively high flow and pres- sure provided by the pump. The vertical ball-check valve shown in the photo (Fig.33-2, lower right) is the original thermosyphon check valve installed in 1987 and still in operation today. It is the legendary “boogie” valve, manufactured by Zomeworks Corporation, but it is no longer widely available. As an alternative in this plumbing configuration today, an ordi- nary 1” brass swing check valve (with a vertical flap) could be substituted if mounted horizontally and tilted slightly downward toward the bottom tee.


20/20 hindsight It is always valuable to learn from the past, unless you


enjoy reinventing the wheel every few years. In this instal- lation, we found some things that worked great and some things that could have been better. Generally speaking, it seems that much of our success here can be attributed to controlling and limiting high temperatures. Good Stuff: The thermal mixing worked to keep the plastic tubing


safe from solar overheating. The use of all-copper tubing near the collectors was a


good idea. Keep plastic away from solar collectors. The thermosyphon cooling loop kept the glycol in ser-


vice for a very long time. Direct floor heating with solar glycol works well even without heat exchangers and even without water storage


Page 28/Plumbing Engineer


These articles are targeted toward residential and small commercial buildings smaller than 10,000 square feet. The focus is on pressurized glycol/hydronic systems, since these systems can be applied in a wide variety of building geometries and orientations with few limitations. Brand names, organizations, suppliers and manufacturers are mentioned in these articles only to provide examples for illustration and discussion and do not constitute any recommendation or endorsement. n


Bristol Stickney has been designing, manufacturing,


repairing and installing solar hydronic heating systems for more than 30 years. He holds a Bachelor of Science in Mechanical Engineering and is a licensed mechanical contractor in New Mexico. He is the chief technical offi- cer for SolarLogic LLC in Santa Fe, N.M., where he is involved in development of solar heating control systems and design tools for solar heating professionals. Visit www.solarlogicllc.com for more information.


In this series of articles, I have been making the case that


the key ingredients for solar/hydronic design and installation can be divided into six categories, listed below, roughly in order of their importance. 1. RELIABILITY 2. EFFECTIVENESS 3. COMPATIBILITY 4. ELEGANCE 5. SERVICEABILITY 6. EFFICIENCY


The success of any solar hydronic home heating installa-


tion depends on the often-conflicting balance between any of these six principles. Finding the balance between them defines the art of solar heating design.


The views and opinions expressed in this column are those of the author and do not reflect those of Plumbing Engineer nor its publisher, TMB Publishing.


April 2011


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