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On 2/7/2011 5:36 PM, Lawrence Lile wrote:
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<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);">>We have been in the practice of turning the
heater on when we are getting ready for a bath to avoid the
standby heat losses <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);">(Energy $$) from continually heating the water. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);">Eli, let’s think about this assertion. How much
energy do you actually save by turning off the water
heater? <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);">OK, one second before you turn it off, the losses are
X. This is a function of insulation, temperature of water,
temperature of the space, but it is going to be a pretty
constant number for a given installation. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);">One second after you turn it off, you are saving a
bunch of electricity! Great! But the losses remain the
same – the temperature of the tank hasn’t changed
significantly, you are still losing X amount of energy that
you already paid for, driven by temperature difference. Are
you saving any money yet? Nope, you are still losing energy
that you’ve already paid for. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);">Let’s say you leave it off for an hour. In that
time, the tank will lose enough heat to drop in temperature
a little, but not much. Your losses, driven by temperature
difference, are still approximately X. You already paid for
that heat, so you still aren’t saving any energy. Same for
two hours, three hours, and beyond. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);">Then you turn it on. The thermostat kicks in, and
the heating element replaces all of the heat that just
leaked out. How much energy did you save? NONE. You put
back in energy that was leaking out in losses during the
whole night. The losses never stopped. You put the energy
that was lost back in the morning. You didn’t save a watt or
a red cent. </span></p>
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<br>
There will still be a minor savings from turning off the heater
overnight, however this savings is unlikely to outweigh the
inconvenience and family hassles involved.<br>
<br>
The savings come from the change in the rate of heat loss between
maintaining a higher temperature tank over the time period vs the
lower rate of heat loss in any relatively cooler tank. Heat loss
(and heat gain) increases in proportion to the temperature
differential between the two locations. (A temperature gradient
forms between the two). Larger temperature differentials lead to
significantly higher heat loss. By decreasing the temperature
gradients, you can decrease energy losses in a heat storage system.
This is part of the concept behind turning down the heat in a
conventional forced air house overnight.<br>
<br>
Another factor overlooked in nearly all water heater comparisons is
where the 'lost' heat actually goes. If the water heater is in the
living space/finished basement/etc any heat that escapes from it
goes to heat the house. This is NOT a problem in heating dominated
northern climates. It is only a problem in cooling dominated
climates. By similar measure, air source heat pump water heaters
are a mixed blessing in heating dominated climates because they will
make your furnace work harder because they cool the area they are
in. Measuring how much harder may be difficult because the water
heater load is small compared the whole home heating load in most
homes.<br>
<br>
-hk<br>
<br>
<br>
<blockquote
cite="mid:AC254829C2A6324CB4DF94CED1DB37FB663A12E52C@exchange"
type="cite">
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<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);">If you let the water heater cool all the way off, to
room temperature, then finally the losses stop altogether.
That will take a couple of days with a well insulated water
heater, not overnight. In this case you really are saving
energy by turning off the water heater. But that isn’t
overnight, that is a week of vacation.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);">If your water heater cools off a lot during the
night, then the losses, driven by temperature difference,
will be a little smaller than X. But if this is happening,
you need insulation, not a switch. Wrap that tank up! A
good tank ought to lose 5F or less overnight with no power.
Wrap up your pipes, especially near the water heater where
they stay constantly warm, as they are heat leakers. Put
those little heat trap thingies in the pipes to prevent
thermosyphoning. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);">You won’t save any significant energy by turning your
water heater off at night. You will suffer the scorn of a
wife who has taken a cold shower, which is much worse than
any energy bill let me tell you. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);">A modern, high efficiency electric water heater, such
as the best model Whirlpool available at a lot of hardware
stores, has so much insulation as to make the standby losses
almost negligible. You can add more if you wish. Compare
the price of one of these well-made units with a tankless
and you’ll realize the tankless is a pretty bad deal. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);">Tankless can save 50% over a crappy 1950’s water
heater with ½” of bad insulation, no heat traps, and bare
pipes right next to the heater. It cannot save much at all
over a modern, good quality tank water heater, not the
cheapest model but the best models, especially with an extra
wrap of insulation. It will cost you a lot more to buy and
install a tankless, it will take a bigger and more expensive
electrical circuit, and you’ll be frustrated with limited
water flow and sometimes variable temperatures (Brrr). <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);">I’ve been through the whole tankless craze, put
several of them in various houses, and began to realize I’d
been sold a bill of goods when I did the math on newer water
heaters. Keep It Simple, Simon and put in a good quality
tank. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);">--Lawrence<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family:
"Arial","sans-serif"; color: rgb(31, 73,
125);"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size: 10pt;
font-family:
"Tahoma","sans-serif";">From:</span></b><span
style="font-size: 10pt; font-family:
"Tahoma","sans-serif";">
<a class="moz-txt-link-abbreviated" href="mailto:greenbuilding-bounces@lists.bioenergylists.org">greenbuilding-bounces@lists.bioenergylists.org</a>
[<a class="moz-txt-link-freetext" href="mailto:greenbuilding-bounces@lists.bioenergylists.org">mailto:greenbuilding-bounces@lists.bioenergylists.org</a>]
<b>On Behalf Of </b>elitalking<br>
<b>Sent:</b> Wednesday, February 02, 2011 9:41 AM<br>
<b>To:</b> Green Building<br>
<b>Subject:</b> [Greenbuilding] Max Temp Storage Water
Heaters+Temperature Sensors<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size: 16pt;">I am
replacing a water heater that is in a location that is
inaccessible for servicing. We have been in the practice
of turning the heater on when we are getting ready for a
bath to avoid the standby heat losses <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;">(Energy
$$) from continually heating the water. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;">I want to
know the maximum temp that typical storage electric water
heater can safely accommodate. Since we are not storing
the heat, the higher temperature is not an energy
penalty. The higher temp allows for a smaller tank. We
are separating the kitchen use from the bathroom. Tank
will located next to the bathtub. We will have an on off
switch at the tank. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;">Does
anybody know of a heat sensor and or sound indicator when
the water reaches a set temperature? Currently we allow
more time than is necessary because we want to avoid being
too cool. It sure would be nice to know what is going
on. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;">We could
use a 20 gal tank for 20 gal bath and set at temp for
bath. However, we use a cistern. During dry spells (most
of the time) we mix creek water in bath to reduce water
usage off of cistern. Results of my spread sheet below
show that 20gal bath can be supplied with 10gal HW tank at
185F. Can a normal temperature relief valve store that
kind of pressure-temperature?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;">Bath (gal)
20.0 <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;">Bath
Weight (#) 160.0 <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;">Bath Temp
(F) 120.0 <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;">Cold Water
(gal) 10.0 <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;">Cold Water
(#) 80.0 <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;">Cold Water
Temp (F) 55.0 <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;">Hot Water
(gal) 10.0 <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;">Hot Water
(#) 80.0 <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 16pt;">Hot Water
Temp (F) 185.0 </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size: 16pt;"> </span> <o:p></o:p></p>
<p class="MsoNormal"><span style="font-size: 16pt;">
Thanks for your consideration.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size: 16pt;">
Eli</span><o:p></o:p></p>
</div>
</div>
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