DHW hot recirc

Mark Eatherton

The best visual example I can give for H.E.C. is the Grand Canyon...

The same thing will happen to your pipes under a continuous circulation condition when velocities are excessive.

Here are some pictures of the conditions that result from HEC.

http://images.google.com/images?client=safari&rls=en-us&q=erosion+corrosion&oe=UTF-8&um=1&ie=UTF-8&ei=ztvpSd66HOCLtgfi8qHRBQ&sa=X&oi=image_result_group&resnum=5&ct=title

ME

Metro Man

DHW hot recirc

Heard a new one today. DHW hot recirc lines where wearing out because of grit in pot. water????

New one on me.... maybe too much pump or possible well water issues.

Anyone ever hear of this?

Also anyone use a bronze Wilo and set waaaaay down and run 24/7? Seems like 5 watt range and slow circ could be a good thing.

Grats in advance.

Metro Man

Mark Eatherton

Buh Low Knee...

I've been here my whole life (56 years) and have NEVER heard of that.

Sounds more like an unknowledgeable first year plumbers apprentice making up a story to sell a new system.

I don't remember who it was, but someone posted some good basic information about circ returns recently.

High, continuous velocity os the pipe killer, and these systems really don't need that much velocity to do the job. TImer and aquastat should be mandatory as well IMHO.


The biggest problem is the mind set of "If a little pump does a little good, then a LOT of pump will do a LOT of good..." and all it really does is a LOT of damage (Hydraulic Erosion Corrosion).

ME

Metro Man

con cur

Yep Mark I agree. Sounded a little out there. Just thought I'd throw that out to the Wall-eye's for feedback.

003B, timer, and aquastat. Going to throw a Wilo B on next one for laughs and grins and crank 'er down.

BTW - you got me by 6yrs you old fart. Did you fire your solar system yet?

Metro Man

jp_2

why the aquastat?

surely you can clock the time its take to circulate hot water, that will change very little over time.

Metro Man

control

EZ and accurate to control especially on bigger homes. Usually run timer when there may be demand (6am - 10pm) and set aquastat to 110 ish. Pump will cycle when needed.

Metro Man

[Deleted User]

Diversions and bad weather...

Haven't done my system yet.

To JP, the reason for the aquastat is so that it shuts off the pump if its not necessary. Not so much for energy conservation as it is to keep the pipes from going away. Although it DOES conserve energy.

ME

Henry

I had a condo that had a reciculation pump on every downriser in the 15 story building. The hot water pipes were M type. After 10 years, we kept repairing pinholes every few weeks, usualy behind the kitchen cabinets! I modified the system to use only one of the existing S25 bronze pumps. No further pipe erosion wa detected or fixed. I had a hotel also with some 24 floors that had a similar problem. We replaced the exisitng two pumps with one bronze Grundfos, no more pinholes!

Larry Weingarten

One other choice...

... is demand pumping. www.gothotwater.com developed the idea. Demand systems pump minutes a day rather than hours, so there is less heat loss and less copper erosion. They do need a big pump to quickly charge the main with hot water. If using a small pump, all you need to do is make up for heat loss. If the pipes are insulated and not run underground, the loss is easier to deal with.

Sizing, or keeping the water volume in the hot lines at a minimum is another good strategy for getting quick hot water while wasting little energy and water. Gary Klein has written some good articles on "structured plumbing". I've taught with Gary and it works, as he wakes 'em up and I put 'em to sleep. ;~)

Yours, Larry

jp_2

good point-makes sense

mark, I do understand the convince of HW recirc, though I see no real energy saving? unless you figure the cost of moving the water from the point source vs recirculating it in the house? then theres the greens cost? waste energy or water? big house or little house....all depends I guess.

what do you mean "pipes going away"?

Doug_7

Prevention of velocity erosion-corrosion of copper pipe

The Canadian Copper & Brass Development Association explains the causes and prevention of velocity erosion-corrosion in domestic hot water recirculation systems.

www.ccbda.org/pdfs/is9702e.pdf

Make sure the pump is not too large for the piping and that the piping ends are de-burred. Insulate the DHW piping to minimize the flow required to maintain temperature.

Keep flow velocity under 5 feet / second and preferably in the 2 - 3 feet / second range. Install a throttling valve on the pump discharge and throttle to minimize flow velocity.

Doug