The Story of RHP3
This is a ground mounted system. So drainback is not possible, unless we had a basement to work with and we needed to install a glycol based system. Glycol is technically inferior for large installations due to needing more electricity to pump the thicker liquid, and that same thick liquid (glycol) is not as good at transferring heat as pure water - so you end up not getting as much out of the system as you would otherwise. To intensify the drawbacks - glycol turns acidic if it overheats. So you have to dissipate any extra heat and avoid collector stagnation. This is where we began to get creative. Rather than incur the expense of a heat dissipation system, we rigged up a system of tube covers. These are made from outdoor rated PVC pipe cut in half along the pipe - so we have half round PVC covers that snap on, tube by tube. Other than the maintenance of adding and removing covers as the season change, this has been a no-hassle solution to the extra heat. We ran wires for an overheat system, should we ever need to automate this process. In that case we would hang some finned copper tubing behind the panels and run the hot glycol through that before returning it to the tank. This install required burying insulated copper pipe in such a way that it would not get wet for 50 years or so. Our process used rigid insulation, spray foam for any gaps, and a waterproofing layer. This is a success so far as we only lose 1.5F degrees from the hottest point in the solar panel all the way back to the storage tank (roughly 90 feet, half of which is buried).
System at a glance
System type: Space heating & hot water Collector type: Evacuated tube Number of panels: 10 Heat storage: 620 gallons Freeze protection: Glycol Predicted annual BTUs: 69 million BTU Actual annual BTUs: 55 million BTUs Annual heat load: 100 million BTU Solar Fraction: 55% System cost after rebates: $17,872 Payback: 11 years
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