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  #1   Report Post  
Phil Sherrod
 
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Default Power cost of idle electric water heater

I recently installed an electric water heater to service a guest bedroom
located far from the central water heater. Since water will be drawn from this
heater only when guests are visiting, I plan to leave it turned off to save
power.

But before shutting it down, I decided to take some measurements and calculate
how much it costs to run an idle water heater.

The water heater is an electric GE Smar****er 40 gallon, “lowboy” (squat) unit.
The plate on the unit says it draws 4500 watts, but my measurements show that
it actually draws about 4320 watts (18 amps at 240 volts). The EPA estimated
annual cost of operation is $401.

I used a Supco model DLAC recording clamp-on ammeter to record power (amperage)
over a 3 day interval. During the same period, I used a Supco model DLT
recording thermometer to record the ambient air temperature in the crawl space
where the water heater is located.

Here is a summary of my measurements:
Monitored interval: 3 days
Power draw when heating element is on: 4320 watts (18 amps at 240 volts)
Duty cycle when heater is running: 0.0161 (1.61%)
Average power used (heating watts times duty cycle): 69.55 watts
Temperature of hot water delivered: 114 degrees F.
Average temperature in crawl space during measurement period: 61 degrees F.
Temperature rise for water: 53 degrees F (114 - 61)

When the heater is on, it draws 4320 watts. However, the duty cycle
(proportion of time heating) is only 0.0161 (1.61%), so the average power drawn
is 4320*0.0161=69.55 watts. (On average, the heating element is on 23
minutes/day.)

An average power usage of 69.55 watts over 24 hours works out to 1.669 KWH
(kilo-watt hours) per day.

The EPA average national power rate is 8 cents per KWH. So, using the EPA
power rate, the cost of keeping the idle water heater hot is 13.35 cents/day or
$4.00/month or $48.73/year.

Here in Tennessee, we enjoy relatively cheap TVA power which costs 5.6
cents/KWH. Using that rate, the energy cost is 9.35 cents/day, $2.80/month or
$34.13/year.

The EPA estimated annual cost of operation is $401 (assuming 8 cents/KWH). So
the idle heat-loss cost of $48.73/year is about 12% of the total cost.

If you adapt these figures for another location, remember that the cost is
directly proportional to the temperature difference between the hot water and
the surrounding room temperature, and you must adjust for your KWH power cost.

Phil Sherrod
(phil.sherrod 'at' sandh.com)


Index: power, energy, cost, water heater, waterheater, KWH, energy use, cost of
hot water, hot water cost, efficiency, power rate, electric water heater,
  #2   Report Post  
m Ransley
 
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Default Power cost of idle electric water heater

But who doesnt use their water heater.
I went from 30 $ at 0.12kwh a month electric bill for electric water
heater 1 person to 5 a month gas bill by putting in a gas tankless Its
paid for itself in 2 years. Try your test with real usage.

  #3   Report Post  
Edward Cheung
 
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Default Power cost of idle electric water heater


Nice work on the investigation. My minor comment is that you used a
standard line voltage in your
calculations. How important is this? Probably not much. In my case, I
just checked the voltage change
over one day. It peaked at 123.4V, and the min was 118.6V. If one
assumed 120V, there would be
only about 2% error.

PS My web page related to home power monitoring:
http://www.edcheung.com/automa/power.htm

Phil Sherrod wrote:

I recently installed an electric water heater to service a guest bedroom
located far from the central water heater. Since water will be drawn from this
heater only when guests are visiting, I plan to leave it turned off to save
power.

But before shutting it down, I decided to take some measurements and calculate
how much it costs to run an idle water heater.

The water heater is an electric GE Smar****er 40 gallon, “lowboy” (squat) unit.
The plate on the unit says it draws 4500 watts, but my measurements show that
it actually draws about 4320 watts (18 amps at 240 volts). The EPA estimated
annual cost of operation is $401.

I used a Supco model DLAC recording clamp-on ammeter to record power (amperage)
over a 3 day interval. During the same period, I used a Supco model DLT
recording thermometer to record the ambient air temperature in the crawl space
where the water heater is located.

Here is a summary of my measurements:
Monitored interval: 3 days
Power draw when heating element is on: 4320 watts (18 amps at 240 volts)
Duty cycle when heater is running: 0.0161 (1.61%)
Average power used (heating watts times duty cycle): 69.55 watts
Temperature of hot water delivered: 114 degrees F.
Average temperature in crawl space during measurement period: 61 degrees F.
Temperature rise for water: 53 degrees F (114 - 61)

When the heater is on, it draws 4320 watts. However, the duty cycle
(proportion of time heating) is only 0.0161 (1.61%), so the average power drawn
is 4320*0.0161=69.55 watts. (On average, the heating element is on 23
minutes/day.)

An average power usage of 69.55 watts over 24 hours works out to 1.669 KWH
(kilo-watt hours) per day.

The EPA average national power rate is 8 cents per KWH. So, using the EPA
power rate, the cost of keeping the idle water heater hot is 13.35 cents/day or
$4.00/month or $48.73/year.

Here in Tennessee, we enjoy relatively cheap TVA power which costs 5.6
cents/KWH. Using that rate, the energy cost is 9.35 cents/day, $2.80/month or
$34.13/year.

The EPA estimated annual cost of operation is $401 (assuming 8 cents/KWH). So
the idle heat-loss cost of $48.73/year is about 12% of the total cost.

If you adapt these figures for another location, remember that the cost is
directly proportional to the temperature difference between the hot water and
the surrounding room temperature, and you must adjust for your KWH power cost.

Phil Sherrod
(phil.sherrod 'at' sandh.com)


Index: power, energy, cost, water heater, waterheater, KWH, energy use, cost of
hot water, hot water cost, efficiency, power rate, electric water heater,



  #5   Report Post  
Phil Sherrod
 
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Default Power cost of idle electric water heater


On 29-Mar-2004, Edward Cheung wrote:

Nice work on the investigation. My minor comment is that you used a
standard line voltage in your
calculations. How important is this? Probably not much. In my case, I
just checked the voltage change
over one day. It peaked at 123.4V, and the min was 118.6V. If one
assumed 120V, there would be
only about 2% error


The line voltage will make no difference in the total energy usage, it just
changes the duty cycle.

The water temperature is set by the thermostat. When the temperature drops
below the setpoint, the thermostat turns on the heating element which runs
until the temperature reaches the thermostat's setpoint. If the voltage is
below the standard, less heat will be generated per minute of operating time,
so it will take longer to heat the water and the heater will run longer -- but
it will draw less power while it is running. So as long as you have enough
voltage to generate sufficient heat to balance the energy loss (70 watts in my
case) the same net energy will be used.

What it boils down to (no pun intended) is the law of conservation of energy:
to maintain an average temperature in the water heater, the heat going in has
to equal the heat being lost. The duty cycle changes, but the total energy
used does not.


  #6   Report Post  
m Ransley
 
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Default Power cost of idle electric water heater

Maybe my water heater is different than yours but when i first turned it
on I wasnt here much showering 4 times a month or so , but my electric
went up 30$ apx , and droped more than that when i went tankless. But
my figures are not documented as yours.
You did the test for 3 hrs, that was with heated water right. What if
the heater full cycled at 3 hr 10 min. You dont know in your test when
the thermostat will call for heat and what that cycle will consume. Im
wondering if a 3 day test wouldnt be more realistic . Water in a tank
retains some heat for 4-5 days, this I know. I just feel but maybe
wrongly that from my past bills Electrics waste alot more electricity
than your findings indicate

  #8   Report Post  
AZ Woody
 
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Default Power cost of idle electric water heater

I live in Phoenix, where there are times my WH is warmer than the temp
setting (it's in my non-AC garage). I do however, have a timer.. Turn it
on about an hour before I wake, and off a few hours later (for weekends).

Basically, I guess what I'm saying, is why NOT run the heater only when
needed? Even if it's only a few extra cents, it adds up - and if enough did
it, it would keep the power companies from building new plants!

Do you turn off the lights if a room is empty? Same thing........


"Phil Sherrod" wrote in message
...

On 29-Mar-2004, Edward Cheung wrote:

Nice work on the investigation. My minor comment is that you used a
standard line voltage in your
calculations. How important is this? Probably not much. In my case, I
just checked the voltage change
over one day. It peaked at 123.4V, and the min was 118.6V. If one
assumed 120V, there would be
only about 2% error


The line voltage will make no difference in the total energy usage, it

just
changes the duty cycle.

The water temperature is set by the thermostat. When the temperature

drops
below the setpoint, the thermostat turns on the heating element which runs
until the temperature reaches the thermostat's setpoint. If the voltage

is
below the standard, less heat will be generated per minute of operating

time,
so it will take longer to heat the water and the heater will run longer --

but
it will draw less power while it is running. So as long as you have

enough
voltage to generate sufficient heat to balance the energy loss (70 watts

in my
case) the same net energy will be used.

What it boils down to (no pun intended) is the law of conservation of

energy:
to maintain an average temperature in the water heater, the heat going in

has
to equal the heat being lost. The duty cycle changes, but the total

energy
used does not.



  #9   Report Post  
Phil Sherrod
 
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Default Power cost of idle electric water heater


On 29-Mar-2004, "AZ Woody" wrote:

I live in Phoenix, where there are times my WH is warmer than the temp
setting (it's in my non-AC garage).


Wow, your garage is 120+ degrees? Do you cook roasts out there too?

In that case, your heat loss from the idle water heater would be $0.00

I do however, have a timer.. Turn it
on about an hour before I wake, and off a few hours later (for weekends).


There's nothing wrong with that, but your savings are probably miniscule. When
you turn the heater on, it is going to run long enough to heat the water to
whatever temperature the thermostat is set for; that might take 15 minutes of
continuous running. The measurements for my water heater show that the total
on-time for the heating element is 23 minutes per day (accomplished by only a
few cycles per day).

Let's say the average temperature in your garage is 85 degrees (vs. 61 in my
crawl space) and your water temperature is the same as mine -- 114 degrees.
You've got a temperature differential of 29 degrees, and I've got a
differential of 53 degrees. Then your cost of heat loss (assuming 8 cents/KWH)
is about $3.28 per month. I would be surprised if your timer dropped the
average water temperature enough to halve the heat loss, so you may be saving
$1.50/month if you're lucky.

Do you turn off the lights if a room is empty? Same thing.


No it's not the same thing. When you turn on your water heater, it runs until
it heats the water to the set temperature; the longer it was off, the longer it
has to run to make up for the temperature drop. Unless it's off for a long
time, the energy required to restore the temperature will come close to
matching the energy that would have been required to hold the temperature
constant. On the other hand, when you turn on a light, it doesn't have to
make up for the darkness that existed while it was off.
  #10   Report Post  
Chuck Yerkes
 
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Default Power cost of idle electric water heater

How much power does it take to go from a "cold" start to heated?
Or even from partially cool back to "running"?

For a guest house the notion is straightforward - turn it off when
nobody's there.

But I see these "energy saving" devices that turn off the heater in
the day. My understanding is you use up that energy getting the
water back to its running temp. That you'd do better to insulate
the heater if it's losing that much.

But when my heater needs replacing, we're going for an
'insta-hot'/on-demand type one. Lower costs in the long run
and infinite hot water.

Phil Sherrod wrote:

On 29-Mar-2004, Edward Cheung wrote:


Nice work on the investigation. My minor comment is that you used a
standard line voltage in your
calculations. How important is this? Probably not much. In my case, I
just checked the voltage change
over one day. It peaked at 123.4V, and the min was 118.6V. If one
assumed 120V, there would be
only about 2% error



The line voltage will make no difference in the total energy usage, it just
changes the duty cycle.

The water temperature is set by the thermostat. When the temperature drops
below the setpoint, the thermostat turns on the heating element which runs
until the temperature reaches the thermostat's setpoint. If the voltage is
below the standard, less heat will be generated per minute of operating time,
so it will take longer to heat the water and the heater will run longer -- but
it will draw less power while it is running. So as long as you have enough
voltage to generate sufficient heat to balance the energy loss (70 watts in my
case) the same net energy will be used.

What it boils down to (no pun intended) is the law of conservation of energy:
to maintain an average temperature in the water heater, the heat going in has
to equal the heat being lost. The duty cycle changes, but the total energy
used does not.



  #11   Report Post  
AZ Woody
 
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Default Power cost of idle electric water heater

It's gotten to 120 OUTSIDE the garage, in the shade! (hotter inside).

Water pipes are also not deep, so on hot days, "cold water" can be warm
enough to bathe in!

During the winter, when it gets a "chilly" 65 in the garage at night, the
extra "kick" to the WH is nice.... (I don't need hot water at 2am on most
days!)

Let's say the timer saves me $.05/day for 6 months of the year.. That's
about $10/year. The timer cost about $25, 10 years back, so I've got $75
more than if I didn't!

Now, I also have a programmable thermostat, and that's save me another
$150...
Then there's the $20 I spent on weather stripping and saved me another
$90...
etc....
It all adds up......

"Phil Sherrod" wrote in message
...

On 29-Mar-2004, "AZ Woody" wrote:

I live in Phoenix, where there are times my WH is warmer than the temp
setting (it's in my non-AC garage).


Wow, your garage is 120+ degrees? Do you cook roasts out there too?

In that case, your heat loss from the idle water heater would be $0.00

I do however, have a timer.. Turn it
on about an hour before I wake, and off a few hours later (for

weekends).

There's nothing wrong with that, but your savings are probably miniscule.

When
you turn the heater on, it is going to run long enough to heat the water

to
whatever temperature the thermostat is set for; that might take 15 minutes

of
continuous running. The measurements for my water heater show that the

total
on-time for the heating element is 23 minutes per day (accomplished by

only a
few cycles per day).

Let's say the average temperature in your garage is 85 degrees (vs. 61 in

my
crawl space) and your water temperature is the same as mine -- 114

degrees.
You've got a temperature differential of 29 degrees, and I've got a
differential of 53 degrees. Then your cost of heat loss (assuming 8

cents/KWH)
is about $3.28 per month. I would be surprised if your timer dropped the
average water temperature enough to halve the heat loss, so you may be

saving
$1.50/month if you're lucky.

Do you turn off the lights if a room is empty? Same thing.


No it's not the same thing. When you turn on your water heater, it runs

until
it heats the water to the set temperature; the longer it was off, the

longer it
has to run to make up for the temperature drop. Unless it's off for a

long
time, the energy required to restore the temperature will come close to
matching the energy that would have been required to hold the temperature
constant. On the other hand, when you turn on a light, it doesn't have

to
make up for the darkness that existed while it was off.



  #12   Report Post  
BruceR
 
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Default Power cost of idle electric water heater

Another option to cosider, particularly for a guest house situation, is
a tankless heater. Available in both electric and gas and in various
capacities they provide a continuous supply of hot water when running
and use no energy when the water stops flowing. I have two gas fired
tankless unit, one for each side of the house. We can run mutiple
showers simulteaneously an both and we never run out of hot water. When
turn off the water the heater goes to sleep til next time. No waste.

From:Chuck Yerkes


How much power does it take to go from a "cold" start to heated?
Or even from partially cool back to "running"?

For a guest house the notion is straightforward - turn it off when
nobody's there.

But I see these "energy saving" devices that turn off the heater in
the day. My understanding is you use up that energy getting the
water back to its running temp. That you'd do better to insulate
the heater if it's losing that much.

But when my heater needs replacing, we're going for an
'insta-hot'/on-demand type one. Lower costs in the long run
and infinite hot water.

Phil Sherrod wrote:

On 29-Mar-2004, Edward Cheung wrote:


Nice work on the investigation. My minor comment is that you used a
standard line voltage in your
calculations. How important is this? Probably not much. In my case,
I just checked the voltage change
over one day. It peaked at 123.4V, and the min was 118.6V. If one
assumed 120V, there would be
only about 2% error



The line voltage will make no difference in the total energy usage,
it just changes the duty cycle.

The water temperature is set by the thermostat. When the
temperature drops below the setpoint, the thermostat turns on the
heating element which runs until the temperature reaches the
thermostat's setpoint. If the voltage is below the standard, less
heat will be generated per minute of operating time, so it will take
longer to heat the water and the heater will run longer -- but it
will draw less power while it is running. So as long as you have
enough voltage to generate sufficient heat to balance the energy
loss (70 watts in my case) the same net energy will be used.

What it boils down to (no pun intended) is the law of conservation
of energy: to maintain an average temperature in the water heater,
the heat going in has to equal the heat being lost. The duty cycle
changes, but the total energy used does not.



  #13   Report Post  
Richard J Kinch
 
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Default Power cost of idle electric water heater

Phil Sherrod writes:

But before shutting it down, I decided to take some measurements and
calculate how much it costs to run an idle water heater.


Well done. I have performed similar experiments with similar results.
Idling losses are small. The tankless advocates are swindlers, but most
people don't have the critical faculties to understand the swindle.
  #14   Report Post  
Phil Sherrod
 
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Default Power cost of idle electric water heater


On 30-Mar-2004, Richard J Kinch wrote:

Well done. I have performed similar experiments with similar results.
Idling losses are small. The tankless advocates are swindlers, but most
people don't have the critical faculties to understand the swindle.


Not as big as swindlers as the people selling timers for water heaters. Most
people think that turning off a hot water heater for six hours is like turning
off a light bulb for six hours. They don't realize that when the timer turns
it back on most of the energy that was "saved" while it was off must now be
spent bringing the water back up to temperature. The tiny savings is only the
integral of the reduction in heat loss rate due to the small reduction in
temperature differential from the temperature drop which is probably just a few
degrees.
  #16   Report Post  
m Ransley
 
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Default Power cost of idle electric water heater

First If everyone had a tankless water heater that apx 3- 10 %
reduction in overall home utility - energy usage would reduce the need
for new power plants for a few years or in gas*s case keep prices more
stabile .
One major thing not discussed is the energy it takes to heat 40 - 50
gallons , the BTU to heat that water is where waste is , Tankless
heat what they use Immediately. No waste. Tankless are the way of
the future as they are the norm in many countries that import energy. We
in the US have it still real cheap.
Energy savings costs money but there is Payback. My gas tankess will
pay for itself in 2 years over electric tank, a 700$ Bosch.
In energy savings in whatever form, windows, insulation, CFL , more
efficient heating, it is common to only gain 5-15 % per upgrade. But
add them up and you really cut your bills.
It is estimated if everyone went to CFL we would need no new power
plants for 10 - 15 years. Same if everyone got a new Energy Star
refrigerator.
A bill was submitted to congress to make CFLs the bulb of choice in
US, well who defeated it - lobbied against it , the Power companies.
Phil did a good test . It would be interesting to see a use test vs a
gas tankless and one with a insulation blanket, in standby mode.
A good test Phil .
Over the life over a tankless which is 2- 3 times that of a tank 20 -
30 yrs at 10 years just the standby loss would would pay for itself at
08 kwh. At 0.12 kwh over 30 yrs it will pay for itself 4 times or
more over. And with higher rates sooner.
Now who beleives utility costs will remain stabile, no they will be up
200 - 400 % in 20 yrs, increasing Payback time. Tankless are the way
to go.

  #17   Report Post  
Nick Pine
 
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Default Power cost of idle electric water heater

BruceR wrote:

Another option to cosider, particularly for a guest house situation, is
a tankless heater. Available in both electric and gas and in various
capacities they provide a continuous supply of hot water when running
and use no energy when the water stops flowing...


The do have some cycling thermal mass...

When turn off the water the heater goes to sleep til next time. No waste.


What's the wakeup cost?

Richard J Kinch wrote:

The tankless advocates are swindlers, but most people don't have
the critical faculties to understand the swindle.


What's the swindle? A tank-type heater set to a low temp or
a greywater heat-exchanger in series with a tankless might
make for less standby heat loss and a much higher capacity,
while still taking some advantage of off-peak rates.

Phil Sherrod wrote:

Not as big as swindlers as the people selling timers for water heaters...
...when the timer turns it back on most of the energy that was "saved" while
it was off must now be spent bringing the water back up to temperature.


My calcs show a 4 watt timer may be a net energy loss, using more
electricity than it saves. And a big money loss, considiering
the cost of the timer and its installation.

Nick

  #18   Report Post  
Phil Sherrod
 
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Default Power cost of idle electric water heater


On 30-Mar-2004, "BruceR" wrote:

How was I swindled by buying tankless heaters?


There's nothing wrong with a tankless water heater, and they do have the
advantage of providing an unlimited amount of hot water.

The "swindle" (maybe that is too strong of a word) is by salesmen who claim
that the tankless heaters save a great deal of energy and power cost. A
tankless heater cannot save more than the heat lost from a standard tank type
heater. As my measurements show, this is pretty small, typically $4/month.
But you won't get a full $4/month in savings because each time you use hot
water it has to heat up the metal heating unit which then radiates (loses) that
heat when you stop using the water. My guess is that a tankless heater saves
about $2/month in energy loss. So if you have a savings of $24/year and a
tankless heater costs an extra $480 dollars (pretty typical), the payback time
is about 20 years (assuming it lasts that long).
  #19   Report Post  
Phil Sherrod
 
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Default Power cost of idle electric water heater


On 30-Mar-2004, (m Ransley) wrote:

One major thing not discussed is the energy it takes to heat 40 - 50
gallons , the BTU to heat that water is where waste is , Tankless
heat what they use Immediately. No waste.


That is true only for the first hour that a normal (tank) water heater is on.
After that time, the water has reached the set temperature and the energy
consumption (other than by drawing hot water) is just from the heat loss
through the tank. There is a difference between storing energy and consuming
energy.

When you take a hot shower, a fixed number of BTU's are required to heat the
cold water flowing into either a tankless or tank water heater. The heat is
exactly the same unless one has a higher efficiency heating core (unlikely if
they are both electric). So the only difference in energy consumption is due
to the heat loss from the tank while the standard water heater is storing hot
water. What my analysis shows is that this heat loss comes to about $4/month.
That is the upper limit on how much energy (money) can be saved by a tankless
water heater. The actual savings will be less than that because "tankless"
heaters actually have a small tank where the water comes in contact with the
heating element, and the heat from the water in that (small) tank and the metal
around it is lost between the times when you draw water.

My guess is that a tankless water heater saves about $2/month in energy costs.
If a tankless unit costs an extra $480 (pretty typical), then the payback time
is 20 years (assuming it lasts that long).
  #20   Report Post  
m Ransley
 
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Default Power cost of idle electric water heater

Well Phil your calculations on tankless vs tank are not quite accurate.
You also forgot that Tanks unless flushed regularly loose efficiency
every year. I just had a tank replaced in a bldg it had over One Foot
of scale- crap in it after 17 yrs. Now that reduced efficiency apx 20
-25 % . Also buildup scale Hard scale cant be avoided in tanks. Tanks
only go down in efficiency , Tankless don't have these problems , they
don't scale. they remain at their rated as long as the burner is clean.
and last 2 to 3 x longer.

For figures on savings you are wrong. I know people that say the same
as me 25- 50 % in costs of operation. saving 15 - 40 a month.
There are allot of people with tankless , they are how you should base
your opinions. Real world everyday use. Not guesstimates.



  #21   Report Post  
News
 
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Default Power cost of idle electric water heater


"Phil Sherrod" wrote in message
...

On 30-Mar-2004, Richard J Kinch wrote:

Well done. I have performed similar experiments with similar results.
Idling losses are small. The tankless advocates are swindlers, but most
people don't have the critical faculties to understand the swindle.


Not as big as swindlers as the people selling timers for water heaters.

Most
people think that turning off a hot water heater for six hours is like

turning
off a light bulb for six hours. They don't realize that when the timer

turns
it back on most of the energy that was "saved" while it was off must now

be
spent bringing the water back up to temperature. The tiny savings is only

the
integral of the reduction in heat loss rate due to the small reduction in
temperature differential from the temperature drop which is probably just

a few
degrees.


Using high efficiency condensing water heaters will bring different results.
The lower the return temperature the more efficient they are. If you allow
a tank of water to cool and you re-heat it with a condensing water heater
the re-heat is very efficient in fuel use. Just top it up when the t'stat
drops a few degrees and the return water will not very cool at all.




  #22   Report Post  
News
 
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Default Power cost of idle electric water heater


"Richard J Kinch" wrote in message
. ..
Phil Sherrod writes:

But before shutting it down, I decided to take some measurements and
calculate how much it costs to run an idle water heater.


Well done. I have performed similar experiments with similar results.
Idling losses are small. The tankless advocates are swindlers, but most
people don't have the critical faculties to understand the swindle.


Tankless take up far less space than a large cylinder, one its main
advantages. I have seen these used in commercial kitchen on faucets where
they are on for the best part of an hour. They can deliver 12 litres per
minute continuously and never run out. That is 720 litres per hour (190.2
US gallons per hour) running out of the tap. 190 gallons? that is quite a
size of storage cylinder you would need when a small white box on the wall
does it without taking up all that space.



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News
 
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Default Power cost of idle electric water heater


"Phil Sherrod" wrote in message
...
I recently installed an electric water heater to service a guest bedroom
located far from the central water heater. Since water will be drawn from

this
heater only when guests are visiting, I plan to leave it turned off to

save
power.

But before shutting it down, I decided to take some measurements and

calculate
how much it costs to run an idle water heater.

The water heater is an electric GE Smar****er 40 gallon, “lowboy” (squat)

unit.
The plate on the unit says it draws 4500 watts, but my measurements show

that
it actually draws about 4320 watts (18 amps at 240 volts). The EPA

estimated
annual cost of operation is $401.

I used a Supco model DLAC recording clamp-on ammeter to record power

(amperage)
over a 3 day interval. During the same period, I used a Supco model DLT
recording thermometer to record the ambient air temperature in the crawl

space
where the water heater is located.

Here is a summary of my measurements:
Monitored interval: 3 days
Power draw when heating element is on: 4320 watts (18 amps at 240 volts)
Duty cycle when heater is running: 0.0161 (1.61%)
Average power used (heating watts times duty cycle): 69.55 watts
Temperature of hot water delivered: 114 degrees F.
Average temperature in crawl space during measurement period: 61 degrees

F.
Temperature rise for water: 53 degrees F (114 - 61)

When the heater is on, it draws 4320 watts. However, the duty cycle
(proportion of time heating) is only 0.0161 (1.61%), so the average power

drawn
is 4320*0.0161=69.55 watts. (On average, the heating element is on 23
minutes/day.)

An average power usage of 69.55 watts over 24 hours works out to 1.669 KWH
(kilo-watt hours) per day.

The EPA average national power rate is 8 cents per KWH. So, using the EPA
power rate, the cost of keeping the idle water heater hot is 13.35

cents/day or
$4.00/month or $48.73/year.

Here in Tennessee, we enjoy relatively cheap TVA power which costs 5.6
cents/KWH. Using that rate, the energy cost is 9.35 cents/day,

$2.80/month or
$34.13/year.

The EPA estimated annual cost of operation is $401 (assuming 8 cents/KWH).

So
the idle heat-loss cost of $48.73/year is about 12% of the total cost.


That is handy to know. Did you calculate whether more energy will be used
to re-heat from cold when only having the water on when you need it? A
quick recovery water heater may be very efficient as the larger power input
is used for a much shorter time. When you need the hot water it will be
ready quite quickly and no hanging around. I have seen electic water heater
cylinders on push timer switches set for say 2 hours. Then you can't leave
them on 24/7. If you need hot water, push the switch; 15 minutes maximum
later, you have a full cylinder of hot water.

Something like this requires a set like by like test. $48 a year extra for
each household per year is a lot of collective energy. Energy that is
running out and pollutes when used.



  #24   Report Post  
Richard J Kinch
 
Posts: n/a
Default Power cost of idle electric water heater

m Ransley writes:

You also forgot that Tanks unless flushed regularly loose efficiency
every year.


Nonsense. The element is immersed. You tankless advocates seem to have a
mental compulsion to believe against all evidence.
  #25   Report Post  
Richard J Kinch
 
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Default Power cost of idle electric water heater

m Ransley writes:

Over the life over a tankless which is 2- 3 times that of a tank 20 -
30 yrs at 10 years just the standby loss would would pay for itself

at
08 kwh.


Tankless "lifetimes" are promised by swindlers who won't be around when
time exposes their stupid claims. I'll bet you think your Kia will last
10 years, too.

Compact, yet higher throughput: tankless heaters are necessarily less
efficient.

The active controls themselves consume power and waste heat. The
electronics will not survive 10 years, much less 20 or 30.

Tankless "efficiency" claims work by confusing people who are
uncritical, or who think they are critical but know too little, with
selective analysis. Society is filled with neurotics who obsess over
monsters in the closet (water heater leaking money!).

The principles are centuries old. Thermodynamics was largely invented
by distillers trying to improve efficiency making whiskey. There were
charlatans back then claiming it could be done more "efficiently" than
optimized methods. Today they sell tankless heaters.

A bill was submitted to congress to make CFLs the bulb of choice in
US, well who defeated it - lobbied against it , the Power companies.


Childish paranoid fantasy.


  #26   Report Post  
m Ransley
 
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Default Power cost of idle electric water heater

Richard I was refering to gas tank water heaters loosing efficiency as
in the one i removed that had about a foot of scale. Electrics retain
efficiency, but are a pure waste all around unless you have cheap hydro.

  #27   Report Post  
m Ransley
 
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Default Power cost of idle electric water heater

Well rich you really show your stupidity and ignorance on tankless
units. Swindlers like Bosch . Wake the F up. Bosch is a company that
will be around longer than you. Bosch is Germanys, GE, they are a very
large Co . into alot of things .Your car probably has Bosch fuel
injection parts in it.

You say tankless are " Necessarily Less efficient " Boy you really
have to read before you make stupid statements. 83 - 84 % Same as
regular tanks..

You Say The Controls consume power Haa Haa what a maroon you are . Mine
uses 2 D cells , No line voltage Nada. and they are 2.3 yrs old .
Bosch also has a unit with a mini Hydro turbine, No batteries, No line
power.
And your statement of life of the electronics being 10 yrs , More of
your stupid Unfounded gibberish.

Efficiency , well you are a real bozo. But dont beleive my claims of
75 % savings over electric tank, and dont look for others that save You
better stay in your cave.

  #28   Report Post  
 
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Default Power cost of idle electric water heater

m Ransley wrote:

Efficiency , well you are a real bozo. But dont beleive my claims of
75 % savings over electric tank...


How do you calculate this 75% savings?

Nick

  #29   Report Post  
 
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Default Power cost of idle electric water heater

News wrote:

...If you allow a tank of water to cool and you re-heat it with
a condensing water heater the re-heat is very efficient in fuel use.


As usual, News, we need numbers to make this latest vague claim of yours
meaningful, ie 1) interesting vs trivial, and 2) capable of being proved
true or false.

As stated, it's like saying "It's harder to climb stairs from the 1st to
2nd than 2nd to 3rd floors of a house." It is, with greater gravitational
force, but who cares, since the difference is utterly miniscule?

If the difference were non-miniscule, it might still be a waste of time
to discuss, unless we can put the effect to good use in some practical way.

So, exactly what do you mean by "cool"... 80 F?
And exactly what do you mean "very efficient"... 80 or 90%?
And what's your efficiency claim when heating 110 F water to 120 F?
And what's your efficiency claim when heating 80 F water to 120 F?

And how would you put this to practical use? Omit the tank insulation,
so the water quickly cools to 70 F when the heater is off? :-)

Please stop wasting our time...

Nick

  #30   Report Post  
m Ransley
 
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Default Power cost of idle electric water heater

I calculated savings in that my electric bill went down 30 $ and my gas
went up 6-7 $ .
This was removing an efficient Rheem 40 gal electric tank 4 yrs old ,
that was "Energyguide " rated at 420$ a yr at 0.8 KWH. And I had a
Fiberglass insulating blanket on it in a heated basement. I replaced it
with Battery ignition Bosch Aquastar .

BTW for all naysayers the Bosch is rated on " Energyguide " at
188 therms a year or 130 $ It is the THE model that uses the Least
energy by " Energyguide".

My Top quality efficient Rheem rated 420$ a year at .08 or 4992
kwh. At my 0.12 that is 599.04 . The Aquastar rated 188 therm or apx
180 $ at todays prices. There showing a savings of apx. 69% by
government tests not my estimates.

I also find myself more aware of my water heater using cold water more
often.



  #31   Report Post  
Richard J Kinch
 
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Default Power cost of idle electric water heater

m Ransley writes:

Well rich you really show your stupidity and ignorance on tankless
units. Swindlers like Bosch


The swindling is in the advocacy and the selling, not the making.

These things are made in Europe and Japan because their housing stock is so
wretchedly small, expensive, and retrofitted back to medieval times, they
can't afford a few sq ft for a tank water heater. All their appliances are
mini-sized and overpriced. Efficiency or the lack thereof has little to do
with it.
  #32   Report Post  
Richard J Kinch
 
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Default Power cost of idle electric water heater

writes:

How do you calculate this 75% savings?


He went from electric to gas, which is 67 percent savings in itself.

Then he used government estimates instead of actual usage. He didn't meter
the old or the new unit. This is important, since tankless is inherently
less thermodynamically efficient.
  #33   Report Post  
HA HA Budys Here
 
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Default Power cost of idle electric water heater

This argument is getting a little heated. (LOL) let's all take a cold shower
and come back to it tomorrow!
  #34   Report Post  
m Ransley
 
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Default Power cost of idle electric water heater

R . Grinch
You say Europeans and Japanese live in wretchedly small medieval
houses and don't have the room for a tank and use small appliances , Wow
, how wrong you are. To bad you've never lived or traveled in Europe
or been educated . And people are swindled you say because tankless
water heaters are BS . You have to be the dumbest sob ive run into. A
true moron.
As to usage well I see you cant read or comprehend , So i will repeat
the basics for you . My utility bill reduction corresponded with the
governments findings. An apx 75% savings in utilities .

  #35   Report Post  
daestrom
 
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Default Power cost of idle electric water heater


"Phil Sherrod" wrote in message
...

On 30-Mar-2004, Richard J Kinch wrote:

Well done. I have performed similar experiments with similar results.
Idling losses are small. The tankless advocates are swindlers, but most
people don't have the critical faculties to understand the swindle.


Not as big as swindlers as the people selling timers for water heaters.

Most
people think that turning off a hot water heater for six hours is like

turning
off a light bulb for six hours. They don't realize that when the timer

turns
it back on most of the energy that was "saved" while it was off must now

be
spent bringing the water back up to temperature. The tiny savings is only

the
integral of the reduction in heat loss rate due to the small reduction in
temperature differential from the temperature drop which is probably just

a few
degrees.


Exactly right. This is the same as 'setback' thermostats. There *is* a
savings, but it is difficult to calculate/predict the results.

daestrom




  #36   Report Post  
Edward Cheung
 
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Default Power cost of idle electric water heater

I agree that the energy used does not depend on the voltage. However,
it will change the calculation
of the energy used. The parameters that were used in the calculations
were measured except for
voltage.

As you say, the voltage will change the duty cycle of the heater,
keeping the energy use relatively
constant (neglecting line losses). Thus low voltages will lead to high
duty cycles (and vice versa),
so the particular duty cycle measured is associated with a particular
line voltage. That line voltage
was presumed, not measured.

Phil Sherrod wrote:

On 29-Mar-2004, Edward Cheung wrote:



Nice work on the investigation. My minor comment is that you used a
standard line voltage in your
calculations. How important is this? Probably not much. In my case, I
just checked the voltage change
over one day. It peaked at 123.4V, and the min was 118.6V. If one
assumed 120V, there would be
only about 2% error



The line voltage will make no difference in the total energy usage, it just
changes the duty cycle.




  #37   Report Post  
Phil Sherrod
 
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Default Power cost of idle electric water heater


On 30-Mar-2004, "News" wrote:

Using high efficiency condensing water heaters will bring different results.
The lower the return temperature the more efficient they are. If you allow
a tank of water to cool and you re-heat it with a condensing water heater
the re-heat is very efficient in fuel use.


I've never seen a water heater that was designed to condense water on the
outside. In fact, I can't understand how that could possibly happen since the
shell of the water heater will be hotter than the surrounding air.

Moisture condenses when warm air encounters a cooler surface; it does NOT
condense when encountering a warmer surface. Have you ever seen a cup of
coffee condense moisture from the air -- no, of course not. A cool drink like
iced tea condenses moisture.

You may see condensation on the outside of a refrigerator, but you're not going
to see it on the outside of a water heater.
  #38   Report Post  
Mick
 
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Default Power cost of idle electric water heater

This assumes that the water in the heater is cooling down to ambient
every day. The time element is on can be reduced by better insulating
the heater so that energy is not lost to the surroundings and the water
temperature maintained, thus saving more money and having it on demand.

Mick

Phil Sherrod wrote:
I recently installed an electric water heater to service a guest bedroom
located far from the central water heater. Since water will be drawn from this
heater only when guests are visiting, I plan to leave it turned off to save
power.

But before shutting it down, I decided to take some measurements and calculate
how much it costs to run an idle water heater.

The water heater is an electric GE Smar****er 40 gallon, “lowboy” (squat) unit.
The plate on the unit says it draws 4500 watts, but my measurements show that
it actually draws about 4320 watts (18 amps at 240 volts). The EPA estimated
annual cost of operation is $401.

I used a Supco model DLAC recording clamp-on ammeter to record power (amperage)
over a 3 day interval. During the same period, I used a Supco model DLT
recording thermometer to record the ambient air temperature in the crawl space
where the water heater is located.

Here is a summary of my measurements:
Monitored interval: 3 days
Power draw when heating element is on: 4320 watts (18 amps at 240 volts)
Duty cycle when heater is running: 0.0161 (1.61%)
Average power used (heating watts times duty cycle): 69.55 watts
Temperature of hot water delivered: 114 degrees F.
Average temperature in crawl space during measurement period: 61 degrees F.
Temperature rise for water: 53 degrees F (114 - 61)

When the heater is on, it draws 4320 watts. However, the duty cycle
(proportion of time heating) is only 0.0161 (1.61%), so the average power drawn
is 4320*0.0161=69.55 watts. (On average, the heating element is on 23
minutes/day.)

An average power usage of 69.55 watts over 24 hours works out to 1.669 KWH
(kilo-watt hours) per day.

The EPA average national power rate is 8 cents per KWH. So, using the EPA
power rate, the cost of keeping the idle water heater hot is 13.35 cents/day or
$4.00/month or $48.73/year.

Here in Tennessee, we enjoy relatively cheap TVA power which costs 5.6
cents/KWH. Using that rate, the energy cost is 9.35 cents/day, $2.80/month or
$34.13/year.

The EPA estimated annual cost of operation is $401 (assuming 8 cents/KWH). So
the idle heat-loss cost of $48.73/year is about 12% of the total cost.

If you adapt these figures for another location, remember that the cost is
directly proportional to the temperature difference between the hot water and
the surrounding room temperature, and you must adjust for your KWH power cost.

Phil Sherrod
(phil.sherrod 'at' sandh.com)


Index: power, energy, cost, water heater, waterheater, KWH, energy use, cost of
hot water, hot water cost, efficiency, power rate, electric water heater,


  #40   Report Post  
Robert L. Bass
 
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Default Power cost of idle electric water heater

Exactly right. This is the same as 'setback' thermostats.
There *is* a savings, but it is difficult to calculate/predict
the results...


There's yet another element which offsets any savings in winter. Heat loss
from the hot water tank is heat gained for the house. Obviously this isn't
a good thing during the air conditioning season, but for most folks here
that's a lot shorter than the heating season.

Alarm and Home Automation System FAQ
http://www.bass-home.com/faq/masterfaq/faq.htm

Regards,
Robert

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