Solar Thermal and Standing Seam Metal Roof Systems: Perfect Together

There’s been a lot of talk recently about solar photovoltaics being used with metal roofing. We’ve certainly done our share of explaining it—even have a PV system installed on our company roof.

But perhaps the most widely employed rooftop solar technology isn’t electric, it’s solar thermal for heating air and hot water. First, because it’s a lot less expensive to install and second, the payback is excellent.

Passive Solar Thermal System Under Metal RoofingSolar thermal water heating technologies rank among the simplest and oldest solar energy applications—hence they are the most cost efficient means of saving energy costs.

Four solar thermal technologies actually utilize the roof structure. Two of them –the evacuated tube technology and the flat plate collector—use the roof solely as a mounting system. But neither is reliant on the roofing surface for solar absorption. Two other systems employ under-the-roof solar thermal technology, using the standing seam metal roof as a critical component both for its solar absorption and as a means of protecting and prolonging the life of the system. Air-based solar thermal systems capture solar heated air and transfer it to the domestic water supply. Although air collectors are not quite as efficient as liquid collectors in heating water, the systems are simpler and require less maintenance than glycol water heaters. An air collector solar water heater uses the same type of differential control as a liquid system, but the differential is usually higher to account for the lower heat capacity of air.The other under roof solar thermal collection system is installed under the standing seam metal roof before the metal is applied to the deck. The entire system is positioned between the attic roof and the outside roof covering. The standing seam panels become components of the solar collector, heating special structural sub-purlins installed over the existing roof structure. These in turn heat a water/glycol mixture that is circulated through cross-linked polyethylene tubing that is cradled in the purlins. A reflective insulation system below the purlins is installed to help heat the mixture. It consists of a layer or layers of aluminum foil separated by layers of a foam insulation material. After being heated in the collectors, the glycol is pumped through the system, and used in a heat exchange to transfer its heat into a solar pre-heat tank of water. This tank of water stores the heat for use throughout the day or night in all types of domestic hot water applications, including laundry, showers, in-floor heating and heated swimming pools. This system also incorporates an expansion tank to accommodate the fluctuating volume of fluid due to temperature changes in the fluid. Insulated piping controls and plumbing connections are installed connecting the new solar equipment into the homes existing hot water delivery system.Image of an Englert Solar Sandwich

Because the roofing material will radiate heat after it reaches a certain temperature, the system is self-regulating, preventing overheating and component damage when the system is inactive for extended periods of time. And here’s one really neat advantage to this system. The same thermal technology can be reversed at night to provide building and process cooling or, in the wintertime, sending warm liquid back to a snow covered roof where the standing seam metal heats up, melting snow quickly and efficiently.

The building integrated glycol-based system can also be combined with PV laminate solar energy panels on the roof above creating a sandwich of solar thermal energy generation and solar electric power. In combination, these systems can produce substantially more energy per square foot than a traditional solar energy system.

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