Domestic hot water ... or how to spin your wheels without getting anywhere

[Jens]

Our electric meter is read every 2 months and we get billed every two months. I have been looking forward to this particular bill (I can't believe I just said that) because it is very special. For the last two months I have dutifully started Thumper twice a day to get storage tank temperatures up into the 60C range before anyone in the house took a shower. This particular bill was to reveal the fruits of my labour ......
As it turned out, we saved roughly $10 a month
We have heated with alternative energy for a long time. First with wood and now with veggy oil so that aspect is not reflected in this assessment. On the other hand, we have never created what I thought was a large percentage of our domestic hot water with alternative energy. I was expecting to see at least a $30 a month drop in my electric bill to reflect the fact that an average house uses about 30% of it's energy requirement for domestic hot water.
Well, it looks like I was chasing a pipe dream ..... either that or something is seriously wrong in my assessment of the situation. Now I do not keep track of all the electricity we use (but it looks like I will have to), but rather I go by averages. Last billing period we spent $110 per month on electricity, this billing period is $100 per month. Not very scientific I realize but damn, I was hoping for something more here.
We average about 50 kwh of electric power usage per day ...... which seems VERY high to me. Looks like I will have to do some detective work to see where it all goes to.

[TimSR2]

Holy cow Jens...Thats a lot of kwh. Electric baseboard heat  (Typical Van isle setup) I assume? No natural gas?

Tim

[Crofter]

Jens, where are you measuring the 60 deg. C temperature in the tank? How far down does that temperarure go?  I have just recently installed an entirely wood heated 40 Imp gallon tank and it only takes an hour or so to get some very hot water but it is only a small layer near the top of the tank and is soon used up. To heat it all the way to the bottom takes about 10 hours though.

Is your tank a typical two element, two thermostat, flip flop system? I wonder how long of vacation the electricity has with the superheated water from thumper? Even if the top is hot, any new hot water draw will send cold feed water in and kick on the lower element even though the upper is held off by the hotter water near the top.

I wish I had thermometers at about four locations up the tank so I actually knew how much HOT water I had in there and be able to predict how much more stoking I should do without blowing off the the TPR valve. As it is now I only know for sure when the hot tap runs cold or the bottom return line starts to get hot. In between is guesswork

I agree with your average electric usage for hot water and it would have been nice to see a bigger reduction. I need some refinements yet to keep from thermo siphon reversing when I have to let the fire out.

[bschwartz]

Jens, I think you may be doing a good job of reducing your need for electricity for your hot water.  I DO NOT agree with the 'general' belief          "the fact that an average house uses about 30% of it's energy requirement for domestic hot water. "

Granted, I have gas hot water, but.....  in the summer my gas bill is about $20.  $15 of that is service charges, the $5 is gas usage.  In winter my bill (if I use the gas forced air heat) is more like $80.

I live in a 1600 sq. ft. house with 3 people showering every day, several loads through the dish washer each week, clothes etc.

I think my house only uses 5-10% of energy for hot water.  If you are like us, I think you hit it just fine.  Now you just need to use the electricity you generate from thumper for your house.

My wife is VERY understanding of my 'need' to come home from work, start Horton and switch off the grid till we go to sleep.  We live with lots of flashing clocks..........

[Crofter]

Jens, sorry, I didn't understand your system. If you are heating your makeup water that hot then you don't have the problem of the lower element kicking on and drawing juice on the sly!

Our meter is read approximately bi monthly but billed montly, one month being an averaged estimate and the next is a makeup bill, so it takes a while to get a true figure on changes. I know I have lots of phantom loads that could be cut out if I was having to generate every bit of it. The way we are billed in Ontario with all the fixed costs of transmission, billing, debt retirement ect., and a quite low rate per KWhour of usage, conservation is not encouraged or well rewarded.

[TimSR2]

Jens,

If you are not using the baseboards...and there is no other explanation ( hot tub, pool heater, 2 hp cont. duty duck pond pump, big grow show,,? ) there is a problem. You may want to borrow a logging probe and figure out where your kwh are going.

Old electric water heater? I cut my gas bill in half by changing out my 23 year old Amtrol hc-7 hot water heater for a brand new unit of the same model number. Corrosion and slime built up on my copper heat exchange coil and reduced it's heat transfer ability to almost zero. Same could happen on an electric unit.

Tim

[Ronmar]

Jens
  I recall doing some math once IRT a question as to how much money would you save turning off your hot water heater every day when you left the house.  Using some numbers for heat loss from insulated steel tanks in 60F still air, a 50 gallon tank with 1" of insulation and starting at 120F, would drop about 10F in 8 hours...  This was of course assuming proper pipe insulation.  Most domestic tanks I have seen have in excess of 1" of insulation however.  I think I calculated at 10C per KW/HR, with the unused tank cycling on about 2.5 times in a 24 hour period, would cost $.25 per day. Heating a cold tank from 60F to 120F would cost about $.70, so at .10 per KW/HR, the break even point was 3 days...FWIW, I have never confirmed these numbers, just applied references from the engineers toolbox on heat loss.

A fairly easy way to monitor the heating element in a HW tank would involve a 240VAC relay and a battery powered mechanical clock.  Maybe $15 in parts total if relay and clock were purchased new.  Connect the relay coil across the heater element power inputs.  Put the Normally Open contact on the relay in series with the battery input to the clock.  Heater comes on, relay gets energized and completes battery circuit to clock which starts running from wherever it last stopped.  Element shuts off, clock stops.  Write down the time and date you started at, and check back in from time to time to log the accumulated times, preferably before it racks up more than 12 hours of accumulated runtime...  With a fairly constant resistance and voltage input, all you really need to know is ammount of runtime to get a fairly accurate idea of consumption.

As far as age and efficiency go, electric heating elements in hot water tanks differ from gas water heaters in one important aspect.  The heat in a gas water heater has an alternate path of escape up the flue, and only a limited ammount of time to transfer it's heat thru the heat exchanger surface into the water.  An electric element is surrounded by the water, and the heat generated in the element only has one place to go, and that is into the water.  Coat the element with mineral buildup?  well the element just gets hotter, increasing it's transfer rate into the water(and ultimately shortening it's life).  I lived in upstate NY for a few years and we had a lot of lime in the water.  Had a heater element go bad(lower one) and went to replace it.  The lower element was completely buried in lime flakes that had been boiled out of the water and flaked off of the heater element untill it was completely buried in them and could not dissipate enough heat to the water to keep from burning out.  I vacumed about 10 gallons of flakes out of that heater tank...    

[TimSR2]

The electricians on the forum will be able to better direct you about logging amp probes than I can. Sparkies?

Loss of heat exchanger performance is a huge issue that most people are not aware of because it is invisible. My water is really soft here in the GVRD too but my h/w heat exchanger was a huge green slime ball. 125 k btu /hr boiler ran 4 hours to heat 41 gallons to 140f.....  Amtrol recommends an acid treatment once a year for optimum performance.

Tim

[mbryner]

Hey Jens,

Even 42 kwh/day is a lot.  We're a family of 4, w/ all electric stove, etc.  (water heater and dryer are gas), 2 server computers 24/7 w/ 21" LCD's, pond pump 24/7.   Our bill last month was 22 kwh/day (~$60).    Do you have an old freezer in the garage?   Old fridge in the kitchen?   Somebody tapped into your power line?  haha     You definitely have a electricity hole somewhere.

[vdubnut62]

I don't get the whole relay and battery powered clock thing?
What am I missing? Why not just tie a cheap 110 plug in clock to one side of the heating element?
Ron

[Ronmar]

That would work also, but I havn't seen a 110V plug in mechanical clock in quite a while:)  havn't looked either...

[vdubnut62]

Sorry Ronmar, I'm still trying to make the transition from "Hip Dude" to "Old Fart".  Now that you mention it, the only plug in mechanical clocks that I have seen in a while ......are plugged in here, in my house.  Bet you could find one at Goodwill though.
It's getting to be a daily thing,  being reminded of my age.
Sorry all, once again I'll shut up and slink quietly away.
Ron

[AdeV]

It's getting to be a daily thing,  being reminded of my age.
Sorry all, once again I'll shut up and slink quietly away.

I doubt "quietly", at your age (creak, creak)

[bschwartz]

Running on listeroid power prevents me from using those clocks.  Even cheap digital alarm clocks use line frequency for timing.  As my loads come and go, my frequency (well the electricity's...) fluctuates between 58-62 hz.  Makes the clocks useless.  The only ones that work in my house are the 'atomic' clocks that get their time from a RF broadcast from Boulder CO.

[Dail R H]

   Jens,I've tried the catherding thing,,,not for the fainthearted, or impatient,lol,,,,,,,good luck