Posted by DavidMDelaney on December 8, 2006, 4:50 pm
A new page at my web site
"Check valves for entirely passive solar water heaters"
Posted by Solar Mike on December 9, 2006, 5:01 am
Depositing the heated returned water near the top of the heat store creates
excessive thermal mixing within the cylinder. Better to keep internal
stratification and return the warmer water much nearer the bottom.
Posted by nicksanspam on December 9, 2006, 11:42 am
Sounds upside down. Does warm water fall in New Zealand?
Posted by Solar Mike on December 9, 2006, 11:02 pm
That depends on whether the rising warm water from the panel system is
hotter than the water at the top of the cylinder. Mostly its cooler (ie
10 -15 degrees hotter that the cooler water at the bottom of the cylinder
entering the panel) so it sinks thus disturbing the stratification.
Posted by DavidMDelaney on December 10, 2006, 4:47 pm
Solar Mike wrote:
Consider introducing water of a middling temperature to a tank of water
that is warmer at the top than the middling temperature and cooler at
the bottom. Is it better to introduce water of middling temperature
at the top or bottom of the tank?
The dynamics of cool water falling through warm water are different
from the dynamics of warm water rising through cool water. In the case
of cool water falling through warm water, the force producing the
movement is the force of gravity pulling the more dense cool water down
through the warmer water. The cool water forces its way through the
warmer water. In the case of warm water rising through cool water,
the force causing the upward movement is produced by the heavier
surrounding cool water squeezing into and under the warm water at every
level of its rise. As a result, the maintenance of a compact and
steady rising stream of warm water supplied from below in a tank of
cool water is less likely than the maintenance of a compact and steady
descending stream of cool water supplied from above in a tank of warm
water. Rising warm water is impelled by forces that tend to mix the
ascending stream. Descending cool water is impelled by a force that
tends to keep the descending stream compact and unmixed.
This argument implies it's better to introduce middling temperature
water at the top than the bottom of the tank.
David Delaney, Ottawa, Ontario