
Efficient Hot-Water Piping (2013) [pdf] - rudedogg
http://www.garykleinassociates.com/PDFs/15%20-%20Efficient%20Hot-Water%20Piping-JLC.pdf
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DannyBee
So, the article correctly says that efficient copper layouts will beat pex,
but in residential, those layouts pretty much don't exist in practice.

Plumbers are happy to just use whatever fittings, etc, to get pipe where it
needs to go, and rarely, if ever, think about the losses caused as a result
(i'm really not slagging on plumbers or the quality of work, i'm just saying
the average plumber trying to get 4 homes done is trying to get 4 homes done,
not sitting around calculating the most efficient layout for copper pipe when
he discovers a stud in the way nobody planned for).

In the past two brand new houses i've lived in, done to the latest plumbing
code, the amount of hilariously horribly copper layout is amazing.

(I'm sure anybody who does this for real has ridiculous horror stories).

Meanwhile, most pex layouts i've seen perform significantly better in practice
just because they use less fittings. So the attempt to be "as horrible as
copper" fails.

Also pex is a better insulator, so in the real world where pretty much no in-
home copper is insulated, pex holds heat better.

So, yeah, i agree with the sentiment that well thought out, well structured
copper works really well, that doesn't happen to be residential reality, and
hasn't been for a long time. (it's possibly a commercial reality though)

~~~
petre
Pex doesn't insulate as well as PPr (thinner wall) and the fittings always
introduce flow resistance and produce turbulent flow since they go into the
pipe. Thread fittings for Pex area usually leaky. I would never use them
except for serviceable manifolds with easy access, otherwise use press fit
fittings. On the other hand PPr fittings go outside the pipe, just like those
for copper and they're heat fused. PPr pipes are quite freeze-prone, the walls
are thick (6 mm for a DN25 pipe) and glass fibre inserion PPr pipes don't have
such a huge thermal expansion as pipes w/o insertion (only suitable for up to
60..68°C = hot water). Most plastic piping is prone to thermal expansion. PPr
does not look pretty so it should be probably ran through walls and floors.

Copper water pipes should always be insulated with at least 6 mm EPE sleeves
or closed cell elastomeric foam sleeves (better). Even cold water pipes should
be insulated at least in heated or high humidity spaces because of
condensation that forms on the pipe.

~~~
aesh2Xa1
Well, the article explicitly states one should use "outie" style fittings for
PEX. Check the fittings figure on the last page; letter (C).

~~~
japanuspus
Exactly: Modern PEX fitting go on the outside. Where I live (Denmark), PEX is
used almost exclusively for new residential installations, but I haven not
seen an in-pipe PEX fitting since my parents build their house in the 80's.

------
tgb
This is my favorite thing I've seen on Hacker News in weeks: immediately made
me interested in something I had never thought much about before, gave me the
information directly and usefully and got me started on a bunch of related
questions.

Speaking of which: I had always wondered why more plumbing isn't done with
flexible hoses instead of this pipes. Hoses seemed like they'd be way easier
to work with. Now my guess is that hoses generally have unnecessary curves no
matter what and that this increases the pressure lost. Is that right?

~~~
kragen
Most materials will not last long in water, especially hot water with the
various chlorinated organic compounds that result from sterilizing impure
water with chlorine. Copper and CPVC are really rather special! Gaviotas had
to replace the pipes in all of their aluminum-piping rooftop hot-water heaters
with expensive copper when it turned out aluminum could handle chlorine but
not the municipal water at their customer sites. All over the US, polybutylene
piping turned out to only last about ten or twenty years due to unforeseen
issues with chloramine corrosion of the PB pipes and Delrin pipe fittings, but
only where they're under stress. And that's why you can't buy polybutylene
pipe anywhere in the US since 1995.

And it turns out that an unexpected rupture of a water pipe can be very, very
expensive indeed. Especially in a wood-framed structure with sheetrock.
Especially if nobody's home.

So builders are generally very conservative with water pipe materials. Nobody
wants to install the next PB disaster. Building supply companies are even more
so; the PB lawsuit cost Shell a billion dollars.

Garden hoses are usually made from one of two materials: some kind of rubber
(buna?) or PVC plasticized with phthalates. With hot water, neither of these
will last even the 10 years that a lot of PB piping lasted, and the phthalates
will leach out into the water and give it that garden-hose taste.

I don't think the curviness of hoses is generally enough to cause a
significant pressure loss.

As noted in another comment, PEX is sort of flexible and hoselike, and is
seeing a substantial amount of use for water piping nowadays.

~~~
rsync
"As noted in another comment, PEX is sort of flexible and hoselike, and is
seeing a substantial amount of use for water piping nowadays."

Yes, PEX is the flexible tubing material you are thinking should exist.

PEX and sharkbite fittings are like magic - you can plug together arbitrarily
complex water circuits and layouts as simply as building with legos.

I personally use copper piping for very long-lived installations and for
simple, long runs. However, anything complex at the end of the line
(irrigation, pump and well work, filter assemblies, etc.) transitions to PEX
and shark bites.

~~~
JshWright
I keep SharkBite ball valves on hand in every pipe diameter in my house. Twice
now I've had some sort of minor plumbing "emergency" (leaking appliances) that
would have required shutting the water off for a day or more until I could get
it repaired. Having the SharkBites on hand meant I could just stick one in-
line on that branch and leave the rest of the water on while I sorted out the
issue.

~~~
kmeade
I had never heard of SharkBite fittings. As a minimally-competent home
handyman, I thank you for putting me on to them.

Here's a link to an informative and sensible video on SharkBite...
[https://www.youtube.com/watch?v=1E8X1VawLeE](https://www.youtube.com/watch?v=1E8X1VawLeE)

------
ScottBurson
Reminds me of this:
[http://www.chilipepperapp.com/](http://www.chilipepperapp.com/)

I was thinking of installing a couple of these a few years ago, but didn't and
then forgot about them. It's a pump that gets installed near a faucet; you
turn it on when you want hot water; it pulls water out of the hot pipe,
sending it back into the cold pipe (where it circulates back to the water
heater), until it senses that hot water has arrived, when it shuts off.

As I say, I haven't tried it, but maybe I will — seems like an elegant
solution, and works with existing plumbing.

~~~
Neil44
It sounds like a good idea although some water companies are not that happy
with an end user putting water back into the supply. Technically the pipe
under your sink is open all the way back to the reservoir or whatever so
there’s potential for system contamination there. Systems are usually designed
so that syphoning cannot happen if there’s a temporary supply problem also.
This is why cisterns are fed noisily from the top rather than quietly from the
bottom.

~~~
askvictor
A cistern could be fed from the bottom as long as there is a length of pipe
going up (to the highest level of water) then back down. Or using a
valve/backflow preventer.

~~~
Doxin
A length of pipe like that wouldn't prevent the supply sucking back water
though. So that doesn't solve the whole contamination issue.

~~~
Neil44
Yes the pipe would need to rise from the cistern up to higher than the level
of the resevoir, which would not always be practical. The resevoir would not
then be able to fill the cistern over that loop :)

------
seiferteric
These kind of things are fun to think about and tricky to solve. My thermostat
in my hallway for example, if I set to 69, will turn off but it still feels
cold. I used an IR thermometer to see that it is 69 right at the height of the
thermostat, but is a gradient down to the floor where it is like 65. So there
are thermal layers in the house. I started to put a small fan on the floor
blowing up at the thermostat that will both mix the layers and blow the cold
floor temp up at the thermostat. It will kick on and after a bit the whole
house will be uniformly toasty :) I started to think why this kind of thing
was not built in, but it would require air inlets and outlets at ground level
and ceiling level and two thermometers, so it starts to sound too complicated
and expensive. I see why people like in-floor heating now.

~~~
rblatz
Ceiling fans have a switch that reverses the direction it spins. Specifically
for that reason, one direction is for summer and the other is for winter.

~~~
triplesec
This is interesting: I never knew that was the reason. Downwards for summer to
fan you, I presume..? but upwards in winter why? Or am I backwards here?

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sokoloff
Tangentially related and complementary (though in a certain sense, opposite to
this article), I am a big fan of the Evolve TSV shower valves.

Turn the hot water on full while you're getting ready and the shower will run
until the water turns warm and then will slow the water to a small trickle,
minimizing the waste of hot water down the drain with no one in the shower.

When you're ready, step in and pull the lever to restore (instantly hot) water
flow.

[http://thinkevolve.com/products/showerstart-
tsv/](http://thinkevolve.com/products/showerstart-tsv/)

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dv_dt
I solved this problem for a small house w/ oversized hot water pipes by
installing an endpoint electric tankless heater. It had a sensor for incoming
temperature so it would apply electric heat until the hot water from the tank
caught up. The initial phase wasn't as hot as the direct feed, but it made it
comfortably warm (vs the very cold winter water.). Installing that was much
cheaper than adding a return circulation loop - but I wish I had thought of
the option dropping the pipe diameter now. Though it might have still been
cheaper to install the point heater.

~~~
abraae
We're on rain water so I always cringe when running perfectly good water down
the drain while waiting for it to heat up.

It would be great if there was some endpoint heater like you describe, that
ran from e.g. ultracapacitors that could be trickle charged from solar.

And yeah, having just built our house, I wish I had read this article earlier
and learned about using minimally sized piping! Obvious in hindsight.

~~~
dv_dt
For your situation, I would think a mini electric hot water tank at the
endpoint could work as long as you have excess electric, you can dump it there
as heat. It's much cheaper storing as heat instead of in battery or ultracap.
You'd get losses from leakage, but if it's well insulated it could be worth at
least checking out the math.

Ive seen some claims that solar water heating/circulation systems are now more
expensive over their lifetime than collecting the solar as electric and
heating water, but I've never gone through and sanity checked that calc.

~~~
abraae
Sounds good but then when that small tank ran out of hot water, I guess there
would be a period of cold coming through until the main tank backed it up?

Unless the small tank was big enough for most conceivable uses - in which
case, e.g. in the bathroom, it would become a large tank.

A continuous flow unit at least can do what you said in your earlier post,
e.g. instantaneously heat up the cold until it starts coming through hot.
That's why I was thinking the supercaps, they might provide just enough juice
for those 45 seconds or whatever, and also hopefully be reliable enough for
decades of use, like you would expect from a hot water appliance.

------
nkurz
I don't understand his chart on Page 77 showing the amount of water wasted for
the different layouts. He has the Zoned at 12 gallons, and the Manifold at 23
gallons. The note below says that the "estimate is based on 20 cold starts per
day". I'm guessing this means total uses, with some fixtures used more than
once (eg, kitchen sink 3 times and lavatories once)? And "cold start" means
that it's assumed that the time between uses is such that one always needs to
wait for hot water to come all the way from the tank?

The Manifold system is a "home run" with 1/2" to all fixtures except the tub,
and the Zoned system is a mix of 3/4" mains and and 1/2" branches. Since the
direct run should never be longer than the branched run (right?) how can the
system composed of all small pipe waste more water than the system with a mix
of small and large pipe? In a cold start measurement, I'd think the Manifold
would have to come out ahead for every fixture except the tub, which would be
a tie. And thus I'd think that any combination of fixtures would have to come
out better, rather than worse.

(I'm not saying this makes the Manifold approach better overall, just that
something seems off about this numbers)

~~~
nippoo
You're assuming that the water cools instantly and you're always wasting the
run from the boiler to the fixtures. This isn't the case: the big advantage of
the zoned approach is that the trunk will remain warm if you're using multiple
fixtures branched off the same trunk.

So if you have a shower while your washer is in use, you only waste that
little branch of water, rather than the whole trunk (or the home run in the
manifold approach). Or if you wash your hands and have a shower in the same
bathroom within half an hour (for example). With the manifold approach, you
lose the efficiency savings when you use the sink / washer / shower within
half an hour of each other.

~~~
nkurz
_You 're assuming that the water cools instantly and you're always wasting the
run from the boiler to the fixtures._

No, I'm just assuming that the definition of a "cold start" is that the water
is allowed to cool before the next measurement is taken. The alternative
(which I agree is common) is a "hot start". The author defines these terms on
the box on the bottom left of Page 76 (which I don't seem to be able to copy
and paste). Since the chart explicitly says "cold starts", my
question/complaint is that as labelled, I can't see how the chart can be
correct. I agree that measuring a blend of hot and cold starts is probably a
better metric to judge the systems by.

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edmundhuber
Do "smart" tap systems exist? Here's what I'm imagining: * instead of a tap
being a valve that opens or closes, relieving or building pressure, a tap is a
switch that signals.. * to the "smart manifold" that it should start pumping
water (hot or cold) to that output. * if the tap is shut off, the water is
sucked back out of that piping and recycled.

So then you would have instant hot or cold water, instead of any mixing at
all.

Here are some reasons why this is a dumb idea: * can't handle branching, *
pipe networks have "welling points" where water will simply remain by gravity,
and no pumping will get it out.

Has anyone tried something similar?

~~~
jakewins
Pumps are not good at stopping and starting. They like to start, run for at
least a few minutes, and then stop. Each stop/start cycle adds wear to the
pump, as the components inside it are at peak strain and friction when they
speed up and slow down. Forcing a pump cycle each time someone opens a faucet
would cause a lot of maintenance.

This is why wells have pressure tanks, to allow the well pump to run longer
cycles, building up pressure to be released over time in the tank.

There's a second issue in that pipes don't like to be empty: exposing hot and
humid surfaces to free air is a bad combination.

~~~
DannyBee
The stop/start issue is true, but this is also an easily solvable problem.
Variable speed dc pumps are a complete commodity at this point. You see them
on geothermal systems, etc.

It's just the recirculation folks are lazy AF.

