phc july 2011
www.phcnews.com
GREEN SYSTEMS As the simulation engine tallies up the solar provided,
the hot water consumed and the backup heat required over the year, the question is, which collector provides better fuel savings and does climate matter?
Results can be unexpected In a complex system, there are many variables in play,
and the outcome may not be obvious or intuitive. This is a good reason to employ simulation software to inspect and analyze a system as thoroughly as possible. In the case of my simulation experiment, the results were unexpected. I would have guessed that vacuum tube collectors
would be more important in Oregon than in Texas. SAM did not agree. In these simulations, no additional savings came as a result of using vacuum tubes in either location. I would have also assumed that, with identical
collectors, more solar savings can be achieved in Texas than in Oregon. Again SAM disagrees. The results show a little more savings is achieved consistently in Oregon using this configuration. A solar water heater that saved 2632 kWh in Texas annually was saving 2886 kWh in Oregon. Figure 36-1 shows a screen shot of the SAM
“dashboard” showing the monthly savings in Texas. The model used in these simulations seems reasonable
in terms of hot water consumption, equipment sizing and performance calculations. The vacuum tube collectors I have been looking at tend to cost about 50% more than flat plate panels per unit area. Since the simulation model
does not indicate anywhere near a 50% improvement in savings, I can conclude that, under these conditions, the extra cost is not justified by performance. In other climates and conditions of water usage and
temperature, the results could be quite different. Changing the size of the collectors and tanks could also change the outcome. SAM makes it easy to inspect and study these multifaceted interactions. 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. l
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 officer 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 info.
73
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