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.

Thanks, Wayne