1" to 3/4" main for DWHR

[DrBoom]

I've purchased a 42"x4" power-pipe drain water heat recovery system ($450 online!) and I'm trying to decide the best way to plumb it into the supply for our system. We are on well water which, according to the pressure indicators on our filters, maintains 40-55psi on a 1" copper line. The recommended approach for the power-pipe is to pipe through the whole-house cold line. Since the power-pipe has 3/4" copper inlet/outlet, I'm concerned about the impact of reducing the volume/pressure available across the house. Our ability to support simultaneous showers is my primary concern - we have (and are keeping) full flow 2.5gpm shower heads.

I see a couple of options on how to plumb the power-pipe in that I'd like to get feedback on.
1. Cut into the main 1" cold water line as recommended by power-pipe, use 1" PEX to/from the power-pipe (~40 ft of pex round-trip + the copper coil in the power-pipe). If I do this, won't I restrict the flow through the house significantly?

2. I can run 1" pex to the power-pipe and then break into the 3/4" pex running to the master shower. Additionally, I can run 1" pex to our indirect hot water tank. The hot water tank is far from the main water room - could be close to 100' of pex to get there. If I do this, I'll only be restricting the flow to the master shower as the other showers feed branches are inaccessible.

Other, not so obvious options? I think the root of the issue is, what is the impact of going from 1" copper @ 40-55psi to 1" pex to 3/4" power-pipe copper and back to 1" pex to 1" copper on the pressure/flow around the house?

Regardless of which method I use, I intend to plumb in valves to have the ability bypass the power-pipe should that ever be required.

P.S. I've assumed that 1" pex is the right size to run to max out the 3/4" copper on the power-pipe with the different ID of pex, I'm open to changing that size if I should.

Thanks for the help,
Jon (in NH)

 

[Reach4]

. The recommended approach for the power-pipe is to pipe through the whole-house cold line.

The logical thing is that you only pass the water going to the WH, and not pipe the water going to the cold taps or toilets through the recovery heat exchanger. I can't imagine that they would recommend passing the whole-house water through the heat exchanger.

 

[Sponsor]

 

[DrBoom]

The logical thing is that you only pass the water going to the WH, and not pipe the water going to the cold taps or toilets through the recovery heat exchanger. I can't imagine that they would recommend passing the whole-house water through the heat exchanger.

The manufacturer claims you get better performance doing just that because the cold (often very cold here in NH) water gets preheated to require less hot water demand. There are other threads on DWHR systems that seem to indicate this is the correct path. According to the manufacturer not plumbing the cold including the shower(s) cold and the hot water intake will reduce the effectiveness by 25%+.

Any thoughts on the impact of pushing the incoming 1" main through a 3/4" DWHR line before going back to the 1" main?

Thanks, Jon

 

[DrBoom]

FWIW, I installed the power-pipe DWHR system with no apparent negative impact. I'm now going from a 1" copper inbound main from our well pump to a 1" PEX to the 3/4" copper DWHR and then back to the house cold supply via 1" PEX to 1" copper which then distributes around the house using copper and pex. We're able to maintain 3 shower full-flow (2.5GPM) shower heads with no apparent negative impact.

I haven't recorded much data yet but I'm showing at least a 22F rise in the cold water temp during a shower.
Thanks, Jon

 

[Dana]

I doubt that the cold water distribution plumbing is all 1" pipe through the house, or that it ever needed to be. The drainwater heat exchanger only needs to feed the hot water heater and the cold side to the shower taps (and yes it DOES make a difference!), but having it feed the entire cold water distribution system is sometimes easier to implement.

At (3 x 2.5 gpm = ) 7.5 gpm the heat recovery efficiency isn't nearly what it is under the 2.5gpm conditions of NRCAN efficiency test protocol, but it's also likely that you're really not pulling 2.5 gpm from any shower head, unless you keep the water pressure high. A flow of ~2 gpm out of a 2.5 gpm rated head would be more typical. (Test it with a stopwatch and a bucket some time.) A 4 x 42 will deliver low to mid-40s efficiency at 2.5 gpm, but that would drop to mid-30s @ 7.5 gpm.

 

[DrBoom]

Your are absolutely right that 1" isn't throughout the house but I do have 1" going to some of the various distribution points around the house. From what I can get to without tearing out walls, I could only feed 1 shower's cold inlet from the power-pipe. The hot water heater is all the way across the house (tank off of the boiler) so even feeding that would be difficult. with ~100+ft of pipe and several difficult spaces to cut access to. Hitting the whole house was the only practical method for our installation.

I did test before and after for flow and I really do have 2.5GpM on 2 of the 3 shower heads - the 3rd is flow restricted as it is a "rainfall" head. That said, it won't be common for us to use all 3 at once, I just wanted to make sure installing the power-pipe would not negatively impact our ability to do so. From what you are saying, we will lose DWHR efficiency when there are multiple simultaneous showers but we are still in a better position with than without.

From the little data I'm collecting, I think our numbers match the 40% you are predicting. With a single shower, I measured 58F inlet cold which rose to 82F during a shower. I didn't measure the shower temp but I assume it is 100-105F. In the winter, when the ground water is even colder, this should result in even larger energy recovery.

Dana, part of why I installed this system was from your previous write-ups on DWHR systems. Thank you for your thoughtful comments on this and prior threads which led me down this path. I even got lucky and amazon had a 4x42 power-pipe at $450 for some reason. With $150 in parts and a lot of effort (1" pex clamps are hard to close and 1" coiled pex is very hard to straighten as a homeowner), I think we'll make that back in a year or 2 on our indirect hot water from our oil fired boiler.

Thanks again.

 

[Dana]

That's a very decent price point for the R4-42, even lower than EFI's wholesale price from a few years ago! Was it Amazon, or some random outfit /person selling on Amazon? A quick search on that site shows a few PowerPipes selling at Renewablity's standard list price, but a R3-54" at a steep discount. It appears to be direct from Renewability, not a third party- their loss leader item of the day or something? Good find!

With three showers seeing regular use it will definitely be paying for itself, unless #2 oil hangs around a buck a gallon for the next decade or two.

 

[DrBoom]

Not a 3rd party seller and not a warehouse deal. They only had 1 and I'm guessing it had been in the warehouse too long and got clearanced but that's just a guess. Hope someone else can use the R3-54 they are selling cheap.

Thanks again, Jon