questions on stratification of a tank

Brad White_194

I remember back in the late '80s, 1988 or so, a tank was agitating back and forth for the longest time, even in the hot sun.

Next thing you know, Mike Dukakis popped out.

michael_34

stratification of a tank

Here is my question using my own example. I installed a Vaughn solar sepco tank w/ one heat exchanger at the bottom of the tank (solar loop tied to this exchanger). Most other tank heat exchangers are closer to the top of the tank (oventrop). Which is better for stratification. A heat exchanger at the bottom (like the Vaughn) or a tank with heat exchanger up high on the tank. Pretty basic
question.
Thanks,
Michael

hot_rod

both will straify

The Vaughn takes a bit longer with the low point coil, but also the mass of that stone lining seems to slow the temperature stratification, at start up.

I think it also has to do with the temperature the coil is being supplied with. With a boiler suppling the coil at 180- 190F the transfer and stratification seems to be quicker and more pronounced.

With solar, the coil starts seeing flow when the solar collector is about 10- 12F warmer than the tank. Measured at the lower solar sensor point, so a tank with 60F water will be seeing 72F supply from the solar at start up.

So it seems the stratification ties directly to the temperature at the coil. Keep in mind a 4X8 solar panel may produce about 25- 30,000 BTU per DAY. take that across a 5 hour solar window to see what amount of SDHW is reasonable to expect.

The problem I see is extracting heat from an upper coil. Unless the tank is circulated, or mixed, it hard to get much output from that upper coil. HTP expects about 10K from an upper coil, in a still tank, something like 40K if it sees two pumped flows. Like any HX.

Here is a cutaway of the stainless tank Oventrop uses. The lower coil goes from the bottom up about 18".

hr

michael_34

thanks Hot Rod
Michael