In our last post we spoke of a Shuco Slim Line solar thermal heating package that would be used in conjunction with a closed loop radiant loop and a high-efficiency gas boiler to heat the domestic hot water and the radiant loop as needed. This system uses the solar thermal system to preheat only the domestic hot water. The gas boiler then heats all of the radiant system while also acting as a backup for the domestic hot water.
An alternate system is one in which the solar thermal system can heat both the domestic hot water and the radiant loop. A Vermont company, Radiantec, offers two variations of their solar thermal and radiant heating systems that do a good job at handling both. I spoke with Don Vance at length last week about his systems and recommendations for our homes. Don is an extremely helpful guy and provided us a quote for both a radiant system and solar thermal system size specifically for our homes a few months ago.
Radiantec Solar Option I System
Option one uses the concrete slab as well as the earth below the slab to increase the solar energy storage area.
This option is unique in that it is a hybrid system that combines the best of active and passive solar thermal technologies without their respective disadvantages. Radiantec has one numerous awards for this design and has published a 28 page report for the US Dept of Energy (pdf) on their site detailing the benefits of this hybrid system over traditional setups.
While the website recommends up 7-8 solar collectors, Don sized our system at only 3 panels. This is due to our climate conditions, available solar energy and rough heating demand. We have a smaller home that is well insulated and located in a milder climate than Vermont. If we were to add more panels, we would have trouble handling the excess heat generated in the summer and would have diminishing returns on the system as a whole.
Some of the things I like about this system are that it improves the efficiency by utilizing a much larger mass for solar energy storage. This will mean that it will take the mass longer to heat up, but once it reaches the desired temperature, it will remain stable for a number of days without additional heating. Also, this setup has the ability to heat both domestic hot water and the radiant heating system. When the radiant heating system no longer requires additional heat, the system will automatically heat the domestic hot water supply instead.
This system is intriguing and seems to be more efficient than the current setup we are looking at. I still have a few questions about it that need to be resolved and of course there is cost as well.
Radiantec Solar Option II System
Option II from Radiantec is similar except that the radiant loop and domestic hot water are heated together in an open loop.
The key aspect that interested me about this setup was it’s ability to cool the home for free during the summer by running the cold water intake from the city through the slab prior to delivering it to it’s point of use. In the DOE report, Radiantec claims they are able to extract over 50K BTUs per day from a 2-story, 1,400 sf house with a 720 sf slab on the ground floor. Not bad for free cooling.
Both options have the ability to contribute to both domestic and radiant water heating, but if there was a way to combine the efficiencies of Option I with the ability to cool the home during the summer, it would seem like the best way to go for us.
Check out Radiantec’s solar site – www.radiantsolar.com – for a wealth of information and background on these systems.
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