Gas-Fired Single Tank Systems Now Possible
Bradford White now has a natural gas backup solar tank available for single tank SDHW systems.
This means that the old solar rule "You must have a two tank system if your backup is a gas fired tank-style water heater" is now wrong.
It works simply by placing the thermostat sensor for the burner higher up in the tank. That means the lower half of the tank will be cool until solar is available. What seems a little magical is how does the heat reach the top of the tank without heating the bottom of the tank, since the burner is still at the bottom?
Has anyone used one of these?
Does anyone know if there's a solar collection penalty?
Here's the description:
http://www.bradfordwhite.com/images/shared/pdfs/specsheets/507-B.pdf
I've discussed this in a little more detail here:
http://greenbuildingindenver.blogspot.com/2011/08/important-new-solar-tank-from-bradford.html
Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
a different brand but
same concept. We are finding it tends to heat the tank below that mid point more than desired. This of course limits the amount of "cold layer" that the solar sees.
I have been impressed with the layering that the HTP Solar Phoenix offers. In that tank the burner is actually up at the mid point, not just the sensor. I have had one running for 4 years now and I sensored and watched it perform. It layers a nice cold bottom.
hr
Another possible way...
... to do things could be to use a standard two element electric heater and use the upper element port to plumb in the cold feed to a boiler. The lower portion of the tank could then be heater by solar without competing heat sources or stratification issues. I'm sure the manufacturers would love the creative use of their tanks. :~P
Yours, Larry
