Solar Solutions Continued from page 37


skilled electrical installation and some testing to complete. Our software approach was imple- mented, installed and verified remotely and required no addi- tional hardware. The amount of heat recovered may seem small, but if this heat- ing condition occurs several times a day throughout the heat- ing season, the savings will be equivalent to several gallons of heating fuel per month for the rest of the life of the system. This kind of savings justifies the effort to change the software but might not justify the cost of the site visit and hardware installa- tion when doing it the old fash- ioned way. These articles are targeted


Figure 30-2


tion, we wanted to stop heating the boiler room and use the stranded heat for some practical purpose. We changed the settings in the SLIC so that the DHW


pump and the primary pump continued to run after the boiler flame shut down. Since this change required only software instructions, no hardware changes were required. The instructions included some other details like turning off the heat recovery pumps when the temperatures are reasonably low and not trying to do heat recovery when the normal heating functions are operating. You can see in the bottom graph in Figure 30-2 that it takes less than 10 minutes to recover all the useful heat from the primary loop and deliver it to the DHW tank. The temperature rise in the DHW tank is unmistakable, driven entirely by “waste” heat.


Hardware versus software I think it was Amory Lovins who once compared the


pursuit of energy efficiency to dining on a whole lobster. About half the reward is easy to find and comes in large pieces (the tail), but the other half is in smaller pieces and takes more skill and attention to obtain (from the claws, legs and other bits). In our Solar Combisystems, the big rewards are in the “free” energy delivered by the solar col- lectors and the fuel savings of a condensing backup boiler (if included). But the smaller opportunities for ever- increasing energy efficiency are numerous, accomplished simply by moving heat from one place to another at the right time with intelligent control. If we were to try to implement this kind of precise con-


trol using conventional hardware, it would require (at least) a time delay relay and perhaps a set-point or differ- ential thermostat and some other interlock switching to produce the same intelligent heat recovery shown in Figure 30-2. The hardware would require a site visit,


Page 40/Plumbing Engineer


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 rec- ommendation or endorsement. Special thanks to Dr. Fred Milder at SolarLogic for providing the original graphics and data included in this article. 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.


January 2011


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