"Wayne Whitney" wrote in message
. ..
On 2005-10-28, wrote:

"Wayne Whitney" wrote:

I'm interested in comparing two designs of water-water
heat exchanger,
where one side is pressurized and one is not (gravity
flow).

Design #1: Unpressurized flow through 2" copper pipe,
pressurized flow
through 1/2" copper pipe wound helically around the 2"
copper pipe.

Design #2: Unpressurized flow through 1.5" copper pipe
sleeved in a
2" copper pipe. The space between the pipes is
pressurized.

The bottleneck in both designs may be that the
drainwater doesn't
completely cover the inside of the inner pipe.

Indeed, particularly as I am going to be installing this
horizontally
rather than vertically. I could only fit maybe a 2'
vertical unit in
my crawlspace. I'm assuming an 8' horiztonal unit will be
more
efficient than a 2' vertical unit.

I guess my real question is this: design #2 is easier to
build, so is
design #1 enough better to be worth building? Of course,
my plumbing
inspector may not allow the single-walled design #2 and
require the
double-walled design #1. But I'm hoping he will allow
design #2 since
the positive pressurization of the potable water should
mean any leaks
in the single wall won't contaminate the potable water.

I'll just about guarantee that #2 will not be acceptable. A
small leak between the two would not be visable to you - it
will just go down the drain. Then, when the city shuts off
the water for repairs, it will suck your sewage into the
city water. #1 would leak outside where you will see it, and
not offer a siphon path to the city water.

Bob