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Old 01-15-11, 03:26 AM   #1
strider3700
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Default standby losses from the hotwater tank add up

Today was a quite day at the house with us being away most of it. I just check the log of the hotwater heater electricity usage and thought it was interesting



The watts on the right aren't correct, the peaks should be 3800 watts not 4200.

What you see is from midnight to midnight

The first 4 spikes are the heater kicking on to make up for loss to the environment. Each is 4 minutes

The next small plateau is washing up after breakfast. Thats 1 pot and the dishwasher turned on.

Right after that is my wifes quick shower since we where late.

4 more 4 minute spikes while we're out of the house

My shower

2 more 4 minute spikes.

32 of 98 minutes worth of the hotwater tank heating was the tank maintaining it's temperature. 8 minutes was shortly after a big usage of water so I'm assuming it's not restoring 100% of the hotwater right after a usage, it must stratify or something.

the remaining 48 was actual time recovering directly from water usage.

so almost 1/3 of the power my tank uses goes to standby loses. I really wish I had space to add an insulating jacket to see how much it helps. The new tank will definitely be getting one.

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Old 01-15-11, 09:09 AM   #2
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If I understand correctly, you're spending about 3.8kW * (32/60) hr = 2 kWh/day, or 740kWh/yr on standby losses. That's $89/yr at my rates. You should pull an iwilltry and build a superinsulating enclosure for the next one.
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Old 01-15-11, 11:17 AM   #3
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What can you tell us about your hot water tank and what did you use to do this tracking of your hot water heater?
I've never seen a chart like this but I'm convinced that if everyone put a timer on their water heater that we would see a nation wide drop in electrical use.
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Old 01-15-11, 02:56 PM   #4
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My tank is a conventional 40 gallon tank that was mid range when new about 8 years ago with a 9 year warranty. It's electric with 2 elements each at 3800 watts and thanks to some help from here we figured out that only 1 element is on at any given time. It does not have an insulating blanket and I can't fit one because the tank is 1/4" from the metal furnace on one side.
Also of note there are no heat traps in the plumbing, and the majority of the pipe is uninsulated. They insulated up until it goes into the roof. All the plumbing is copper.

Due to not having a tempering valve and having young kids the tank is set to 108-110 F. I'm sure the standby losses at 140 are much worse.

It sits in my heated basement that averages about 19 degrees, dropping as low as 16 at night lately. I can post temperature charts of the room beside it if anyone cares.

For the graph I have an arduino hooked up to two current sensors taking reading every 2 seconds. The current sensors are not calibrated hence the 4200 watts instead of 3800. For my purpose I just care on or off and use 3800 for any acutal kw math.

That is sent to the PC that averages every minute and saves that to csv. I then take that csv each night and check if the average is >300 then it was on if not it's off. THis is to remove noise in the readings. I sum the on minutes for the total and create the graph posted. Complete details on my homebuilt data logger are here
http://ecorenovator.org/forum/applia...html#post11051

My math works out to $60 lost to standby heat. When I get the new tank it will be in at least a blanket and I will insulate the pipes because they will all be exposed.
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Old 01-15-11, 04:00 PM   #5
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Quote:
Originally Posted by strider3700 View Post
It does not have an insulating blanket and I can't fit one because the tank is 1/4" from the metal furnace on one side.
Well then a thin layer of the best insulation you can find on the furnace side, and 12"-16" everywhere else Since it is electric you don't have to watch out for flues, etc. I take it moving either away from the other is out of the question.

Quote:
Originally Posted by strider3700 View Post
Also of note there are no heat traps in the plumbing, and the majority of the pipe is uninsulated. They insulated up until it goes into the roof. All the plumbing is copper.
Well then that 3800W heating element might as well be used as a space heater
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Old 01-15-11, 04:56 PM   #6
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You might even try a silver space blanket wrapped around and see what kind of change that makes.
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Old 01-17-11, 03:57 PM   #7
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With a small amount of insulation, the difference won't be grand, but if the heater cycles on once every 3:00h-3:10h instead of every 2:50h-3:00h, then you should be saving something like 8% while in standby. Not bad
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Old 01-18-11, 03:07 PM   #8
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Jan 17th


THe little spike near 10 at night is due to 1 of the current sensors getting unplugged so only half of the watts are recorded. I seriously need to move off of the breadboard soon. The same for the spike down on the recroom temperature.

Yesterday was easily our lowest hotwater usage with no baths or showers taken at home. Dishwasher didn't run and the one peak was a sanitize diaper load in the washing machine. It's looking like the stand by peaks are more spread out but it's still hard to tell. Maybe 20 minutes longer 2:50 to 3:10 or something.
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Old 01-18-11, 06:45 PM   #9
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Interesting saw-toothed wave of temperature versus time. I bet if you could record temperature with higher resolution, you'd see a different shape. How often does it show that your HVAC cycles on and off?

You can also see that the sun is shining on the thermocouple in the rec. room and the thermostat that controls the office, but not on the thermocouple in the office. It's another illustration that multi-zone HVAC = greater comfort.
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Old 01-18-11, 07:53 PM   #10
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Thats temperature taken every 2 seconds averaged and recorded every minute.

The hump in the orange line is from the woodstove getting refilled and opened up. the abrupt start and end to the climb is from it's fan turning on and off due to it's thermocouple. The sensor in that room is about 12 feet in front of the woodstove so it's really sensitive to the stove and it's fan.

The saw shaped recordings are from the fan in the forced air system kicking on every 15 minutes or so for 5 minutes o it's circulate program. I do this to move the heat from the woodstove around the house. I've actually found that just turning the fan on for 2 hours and then going to circulate does a great job of cooling the recroom with the stove and heating the rest of the house. I intend to eventually connect the downstairs cold air return to the recroom to make it even more efficient.

The rec room gets sun but the office does not on the jan 16th graph around 1 in the afternoon you see this small hump.
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