Electricity bill - OT
tedm at toybox.placo.com
Tue Feb 8 22:02:40 PST 2005
My apologies to posting to this to the list, but I cannot sit by and
let such a crock of misinformation pass without comment. It will be
my last post on this topic here.
> -----Original Message-----
> From: owner-freebsd-questions at freebsd.org
> [mailto:owner-freebsd-questions at freebsd.org]On Behalf Of Chad Leigh --
> Shire.Net LLC
> Sent: Tuesday, February 08, 2005 10:16 AM
> To: Henry Miller
> Cc: freebsd-questions at freebsd.org; Ted Mittelstaedt
> Subject: Re: Electricity bill - OT
> >>> This is a gimmick built to sell houses, a cool one, but only in hot
> >>> climates does it make much difference. In cooler climates the heat
> >>> from the standing water in the pipes just makes the furnace run
> > less,
> >>> thus the savings are a wash.
> >> That does not make sense. The savings is in running the hot water
> >> heater less.
No. The savings is in dumping heat into the atmosphere at a slower rate
of speed. If your water pipes are insulated then the heat that
passes out of them into the interior of the house does so at a slower
rate. If the house is insulated then the heat from the interior of
the house (some of which is heat that comes from the water pipes)
will be lost more slowly.
>>> Houses that care about energy efficiency have the hot
>>> water pipes insulated anyway so it would not help in cooler climes.
That is not true. All insulation does is reduce the speed at which the
heat is lost, it does not stop it. Over a 24 hour period a hot water
pipe will cool down to room temp. Without insulation it may take an
hour. With insulation it may take 10 hours. But it will lose the heat.
And even if the insulation is perfect, the pipe is connected to taps
at the sink and such that are not insulated and will act as heat sinks
and draw the heat out of the pipes.
> >> The goal is to run the hot water heater less, which you achieve when
> >> you constantly circulate the hot water through the hot water pipes,
> >> instead of letting it get cold and have to run a ton when
> you need a
> >> lot of water.
> > That does not make sense. IF the pipes were perfectly
> insulated there
> > would be no need for this loop because the water in the
> pipes would be
> > hot. However there is no perfect insulation, so you keep
> the water in
> > the pipes warm by re-circulating it. Each time water goes
> through the
> > pipes it loses a little heat, which the water heater then has to make
> > up for. So these loops waste energy, but it is considered worth it
> > because you get hot water without having to wait.
> The data I saw a year or two ago showed that these were more energy
> efficient than the standard model of waiting for a minute or two for
> the hot water to purge the colder water from the pipes.
The data you are looking at was almost certainly from the vendor of
the recirculating system which is going to setup a test skewed to
show their product in the best light. For example use insulated
pipes in the recirculating system and non-insulated pipes in the
standing water system. Or raise the water temp 10 degrees in the
standard house - hotter pipes lose heat faster because the thermal
difference is higher.
Another thing is that a lot of these systems are going to flexible
plastic piping that use friction quick disconnects (so any moron
can put it together) The plastic is supposedly rated for 50 years or
so, yadda yadda. Such a system is going to lose heat more slowly than
a copper pipe solution because plastic is a poorer thermal conductor
than copper (remember they make radiators out of brass) all other
things being equal.
If all things are equal, a recirculating system is going to be a worse
system than a non-recirculating system. The reason is that for each
foot of water pipe in the system there is a certain amount of heat lost.
If you insulate then the heat loss is less - but it still exists. A
recirculating system has more pipe and it keeps the pipe hotter so
the thermal difference means the entire system loses heat faster.
Think of it this way - you have 50 feet from the shower and the water
heater. In a standing water system this is charged with 2 gallons
of hot water. When the 50 feet of pipe is at rest, the 2 gallons
in it lose 10 degrees an hour. You have your water heater at 110
degrees and your room temp at 70 degrees. When you turn off the shower
it takes 4 hours to cool down to room temp. After that time the
water loses no heat. So, in effect your dumping heat for 4 hours
from the pipes. When you go to take a shower 24 hours later, you
have to dump 2 gallons of cold water from the shower before it's warm.
In a recirculating system since you have a return pipe you have 100
feet of pipe. (50 foot out, and 50 foot back) The water in the pipe
is kept at 110 degrees. When you take a shower you can get in
without having to dump the 2 gallons of hot water that cooled down
to 70 degrees. But, wait. That 100 feet of pipe has been maintained
at 110 for 24 hours. Like the other system it is losing heat at the
same rate - 10 degrees an hour. (actually faster because since the
thermal difference is kept higher, the heat loss rate is higher) But,
it's losing that 10 degrees on 4 gallons of water - and it's doing it
24 hours, not 4 hours.
It has added
> benefits, and the benefits may be related to this (ie, constantly
> circulating water means you run it less which may be where the savings
> come in). I do not have the data in front of me now, but it was an
> interesting proposition. And more energy efficient. Not a gimmick.
It IS a gimmick. It is a shame that they don't teach kids logic in
these days (actually, they didn't 20 years ago when I was in school,
as 20 minutes of rather enjoyable deductive reasoning could have shown
you that the premise is full of baloney.
Where the savings from the new system to the old system are going to come
in is: insulated pipes, flow restrictors, better positioning of the
water heater in relation to the hot water consumers (no 50 foot runs of
hot water pipe) lower water temperatures, more efficient water heater.
But, you can have all these things in a standing water system too and
save even more money than the recirculating system.
And even if the premise were true, it's going to be blown out of the
water by human use. For example some people like cold showers in the
morning it helps them wake up. Lots of people will turn on their
washing machine right after the shower while the pipes are still hot,
on their way out the door to go to work. People often take showers one
after another so little loss occurs. Some earth-mother types will take
a watering can into the bathroom and dump the purge gallon into it
to water the plants because they can't bear to waste a cup of water.
Some people can't stand cold showers so will jack the water heater up
to 160 degrees (that's me). Others have 4 kids all wanting to take
showers in the morning and so are forced to jack up the water heater
temp in order to have enough hot water.
> >>>> Also, the new
> >>>> tankless HW heaters look interesting...
> >>> those have been around for at least 20 years. As most of them are
> >>> electric, not natural gas, your going to pay more money for heating
> >>> water with a bunch of those than with a central gas water heater.
> >> The ones I have seen, the newer models, are GAS and are very
> > efficient.
> >> Maybe you need to get out more?
> > I've seen both types. Both have been around for 20 years.
> Computers have been around about 50 years, but to compare todays
> computers to those of 50 years go is ridiculous. Do you not think
> that mayb e hot water technology has advanced some in 20 years?
No it actually hasn't - much that is. As I have a 90% efficient furnace
and an expensive efficient water heater that cost 4 times more than the
ordinary kind, I can tell you what the so-called advances are in heating
1) adding timers to electric water heaters so that the heater doesen't
run all day long.
2) more and better insulation in the water heater.
3) Better sacrifical anode design so that the inside of the heater
rust out as quickly. In fact one of the biggest secrets in the business
that if you want your water heater to last forever, just replace the
sacrifical anode periodically, before it's completely eaten up, because
it's eaten up the tank starts rusting.
4) For gas-burners, ducting the intake air around the flue and pulling it
from the outside of the house, so that your not dumping all the inside
that your furnace has heated up, out the water heater's flue.
5) Better heat-exchanger design for gas burners which lowers the flue
temp so that more of the generated heat goes to the water.
6) Electronic spark ignition systems on gas burners so that there's no
7) A realization by home designers that it's a waste of energy to put the
water heater far away from the bathrooms. Modern home designs situate
the sinks, bathrooms, washer/dryer, dishwasher in close vicinity to the
water heater. They also avoid running long runs of water pipe in
8) Use of solar collector pre-heaters on the roof.
9) Manufacturing dishwashers that have heaters in them so that the
heats up the water to washing temperature, so that you can run lower hot
water temperatures in your hot water heater.
10) A massive publicity campaign to try to get people to turn down the
thermostats on their hot water heaters.
> > Electric
> > ones seem more common, but to replace a tank type water
> heater you need
> > 80 amp service to it, which is difficult to work with so few people
> > have or use them.
> I was specifically refering to new technology, I believe gas based,
> tankless water heaters that are more energy efficient and can lower
> your energy needs.
The Bosch AquaStar line is rated at a maximum efficiency of .66 - .78
energy factor, here is the link:
The tanked units on this page range from .62 to .65 energy factor
This is not a particularly large difference. The .05 or so difference
of the tanked models is simply due to the fact that since they have
hot water tanks, those tanks lose heat, whereas a point-of-use
model has no heat loss except when it's in operation.
But this has to be offset by the increased cost of manufacturing several
of these devices instead of just 1 heater, the increased maintainence
costs because now you have many things that can break down instead of
just one, and you have to run gas piping all over the place, and you
have to put in an exhaust vent for each unit.
Where the savings comes in is that they are typically used in locations
where there are very low infrequent usage of water. And in those
situations they save a huge amount of money. But in the typical 2
parent, 2.5 child single family home the point-of-use models save
> To compare this to 20 year old technology is
Not every industry has technological advances at the rate of the
computer industry. Consider that you could take a 100-year-old
telephone set and plug it into the telephone network today, and it
would still work.
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