Grundfos says their "comfort system" uses "less energy than a 25 watt
light bulb," but it looks like that isn't the whole story. A foot of 3/4"
140 F pipe in 70 F air loses 30 Btu/h, about 10 watts, so when it is
running, their recirc pump might add about 1 kW to the power consumed
by a house with 100' of hot water pipe, or more, since Grundfos uses a
pump and a timer at the water heater and doesn't sense temperature at
the distant fixture. It looks like it pumps hot water continuously into
the cold water pipe at the fixture, thus making a lot of the cold water
piping hot and forcing a person wanting cold water to waste hot water
out of the cold water pipe until it turns hot again.

Taco seems to have a better solution. Their $300 006DM-PK plumbing kit
has a pump with a check valve under the sink, and temperature sensors.
I'd omit the preheat pushbutton and use it with a motion detector.

Nick

wrote:

Grundfos says their "comfort system" uses "less energy than a 25 watt
light bulb," but it looks like that isn't the whole story. A foot of 3/4"
140 F pipe in 70 F air loses 30 Btu/h, about 10 watts, so when it is
running, their recirc pump might add about 1 kW to the power consumed
by a house with 100' of hot water pipe, or more, since Grundfos uses a
pump and a timer at the water heater and doesn't sense temperature at
the distant fixture. It looks like it pumps hot water continuously into
the cold water pipe at the fixture, thus making a lot of the cold water
piping hot and forcing a person wanting cold water to waste hot water
out of the cold water pipe until it turns hot again.

Maybe you've been looking at a different Grundfos recirculator Nick.
This one on their website uses a dedicated return pipe. If all the hot
water piping and the return pipe are well insulated, it should provide a
pretty efficient solution.

http://www.grundfos.com/Web/HomeUs.n...256AE9005326AE

However, for existing construction, the cost of installing a return line
and trying to insulate the piping would be a financial nightmare.

Maybe Grundfos has another model which uses the cold water line for a
"return", like the Taco.

Taco seems to have a better solution. Their $300 006DM-PK plumbing kit
has a pump with a check valve under the sink, and temperature sensors.
I'd omit the preheat pushbutton and use it with a motion detector.

Nick


You've analyzed it and figured out the the deficits correctly Nick.
Those systems that pump the hot water back into the cold line are an
expensive solution for what isn't really that big of a problem for most
folks.

Do the numbers yourself Nick. All that "wasted" water the advertisements
blab about really doesn't cost that much, unless your house is located
on the moon.

If water waste bothers you, you can avoid ****ing away a lot more than
that amount of water by developing better washing habits, like not
letting the warer run all the time you are shaving, but turning it on
and off each time you need to rinse the razor. Or, just putting a little
water in the sink and swishing the razor in it. You get the idea...

If the "wait" for hot water and its attendant waste is really bugging
you, the "right way" to correct the problem in an existing structure is
to install an electric "tankless heater" close to the faucets of interest.

Jeff

--

Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"As long as there are exams in public schools there will be prayer in
public schools."

Jeff Wisnia wrote:

wrote:

Grundfos says their "comfort system" uses "less energy than a 25 watt
light bulb," but it looks like that isn't the whole story. A foot of 3/4"
140 F pipe in 70 F air loses 30 Btu/h, about 10 watts, so when it is
running, their recirc pump might add about 1 kW to the power consumed
by a house with 100' of hot water pipe, or more, since Grundfos uses a
pump and a timer at the water heater and doesn't sense temperature at
the distant fixture. It looks like it pumps hot water continuously into
the cold water pipe at the fixture, thus making a lot of the cold water
piping hot and forcing a person wanting _cold_ water to waste hot water
out of the cold water pipe until it turns hot again.

Maybe you've been looking at a different Grundfos recirculator Nick.

The Grundfos "comfort system" has no dedicated return pipe.

This one on their website uses a dedicated return pipe. If all the hot
water piping and the return pipe are well insulated, it should provide a
pretty efficient solution.

Chapter 44 of the ASHRAE Applications Handbook says 1/2" fiberglass
insulation lowers the pipe heat loss from 30 to 17.7 Btu/h per foot.

Maybe Grundfos has another model which uses the cold water line for a
"return", like the Taco.

Yes.

Taco seems to have a better solution. Their $300 006DM-PK plumbing kit
has a pump with a check valve under the sink, and temperature sensors.
I'd omit the preheat pushbutton and use it with a motion detector.

...Those systems that pump the hot water back into the cold line are an
expensive solution for what isn't really that big of a problem for most folks.

Taco wastes less energy than Grundfos, for cold-line systems.

If the "wait" for hot water and its attendant waste is really bugging
you, the "right way" to correct the problem in an existing structure is
to install an electric "tankless heater" close to the faucets of interest.

That would cost more and waste more energy, without a motion detector.

Nick

Personally, I think what you want to do is a silly waste of energy and
money. You've got more important things to worry about. Having said
that, if you have to have this, I'd add a tankless unit in the
bathroom.

Childfree Scott wrote:

...if you have to have this, I'd add a tankless unit in the bathroom.

They cost a lot and keep a small amount of water hot all the time.
You might compare the capital and energy costs of the tankless and
Taco solutions, with a motion detector that moves hot water for 30
seconds, using actual numbers.

Nick

wrote:

Childfree Scott wrote:


...if you have to have this, I'd add a tankless unit in the bathroom.


They cost a lot and keep a small amount of water hot all the time.
You might compare the capital and energy costs of the tankless and
Taco solutions, with a motion detector that moves hot water for 30
seconds, using actual numbers.

Nick


Yes, but if it's in a john, howya gonna keep that motion detector from
causing it to waste energy for 30 seconds every time you go in the to
take a leak?

To save your wasting bandwidth by telling you have to wash your hands
every time, I'll tell you now that we MIT guys know how to urinate
without ****ing on our hands. G

Are you maybe at Vilanova writing a Master's thesis on this subject or
something? Methinks you are straining at a gnat. GG

Jeff

--
Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"

I have been interested in building a new plumbing system with hot water
recirculation. I just found this install guide from Grundfos that has some
good information (PDF file)

http://www.us.grundfos.com/web/Download.nsf/Pages/D6774D5BEBD2117B8825652200650E2C/$File/Uprec-gd.pdf

--
Jedd Haas - Artist
http://www.gallerytungsten.com
http://www.epsno.com

The way that they have it drawn it will work without the pump. Heat
rises and cold falls so all you need to do is bring a return from the
last hot water connection to the water heater drain with an extension,
put a flap type check valve installed at a very slight angle so the flap
hangs open on the return line. Then when you turn the hot water on the
flap closes and you don't pull cooler water into the loop.

I did this in my ranch type house and it worked great, but used energy
as you have a constant loss. But its a trade off for convenience.

Rich






"Jedd Haas" wrote in message
...
I have been interested in building a new plumbing system with hot water
recirculation. I just found this install guide from Grundfos that has
some
good information (PDF file)

http://www.us.grundfos.com/web/Download.nsf/Pages/D6774D5BEBD2117B8825652200650E2C/$File/Uprec-gd.pdf

--
Jedd Haas - Artist
http://www.gallerytungsten.com
http://www.epsno.com

Bosch Aquastar has many units, you can get an old pilot model if you
wish to waste energy or one of the newer models most people buy. 2 of
them require no outside electricity supply, one has battery ignition ,
which I have, and one has a mini hydro generator. I dont see any more
delay than with a tank.

Recirculators waste energy.

Electric tankless heaters for most of the US cost double to operate
than gas and easily require you to upgrade your main as a good Bosch
unit takes apx 120 amp itself to operate.

m Ransley wrote:

Bosch Aquastar has many units, you can get an old pilot model if you
wish to waste energy or one of the newer models most people buy. 2 of
them require no outside electricity supply, one has battery ignition ,
which I have, and one has a mini hydro generator. I dont see any more
delay than with a tank.

No more delay? :-)

Recirculators waste energy.

The Taco system is close to the manual method, with less water use.

Nick

My Bosch pilotless has a 4 second delay from faucet turn on till full
fire. Not a delay worth considering. My 2 d cells are 2.7 yrs old ,
maybe new batteries would get it down, but still not worth mentioning at
4 seconds, and zero standby loss, it is pilotless.

Correction, I just went back and took off my Waterpick restrictive tap
filter and got a 3 second delay.