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."