DSeitz56
New member
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- Bentonville, AR USA
Does the NEC allow for diversity for Instantaneous Electric Water Heaters when calculating load?
Instantaneous Water Heaters
- Thread starter DSeitz56
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JoeStillman
Senior Member
- Location
- West Chester, PA
It's not much of a demand factor, especially for those monstrous instantaneous heaters, but i'ts all I can come up with.
JoeStillman
Senior Member
- Location
- West Chester, PA
The ironic thing about instantaneous water heaters is that, even though they draw about 1.21 Giga-Watts, you can save energy because they have no losses from maintaining a 30-50 gallon tank at 120 degrees.
Another ironic thing about most whole house installations is that your shower is still cold
kwired
Electron manager
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- NE Nebraska
Another ironic thing, especially in colder climate areas, is that payback is longer than one thinks. That lost energy from a tank - style heater simply lessens the heating load of the building, but does increase cooling load. If you live someplace where you run the cooling more than the heating, it may be worth looking into. Otherwise you often times end up spending a lot of extra $$$ providing large enough service to handle the instant water heater plus remaining load that it does not pay for itself in energy savings in a short enough period of time to be worth the investment.
Which I have measured at about 50w. This would cost me $66/yr.
I put an hour meter on my 50 gallon 4500 watt electric water heater and found that it runs about 3.61 hours a day on average for a 60 day period starting from october to now. Looking at different size units for individual rooms and whole house units, i couldn't beat the 50 gallon unit with my 5 member family.
What's your incoming water temp? What's your heater set to?
This is 3 kwh of energy to provide hot water, per person per day.
Normal total water usage is 70 gals per person per day and half may go to lawn watering.
I put an analog clock between the neutral and a hot lead, set to midnight when everyone went to bed, and the next morning it advanced 5 minutes in 5 hours (B4 I added insulation) and 5 minutes in 7 hours, after.
5 min/5 hours x 4500w = 75w.
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kbsparky
Senior Member
- Location
- Delmarva, USA
You didn't hook it up right.
In the first place, there ain't no neutral in a 240 Volt water heater. Secondly, if you did manage to find a "neutral" connection (or by using the ground as a rogue neutral), connecting to only one side of an element's terminals would result in the clock running inaccurately, since the thermostats only interrupt one side of the incoming line.
OTOH, if you were using a 240 Volt clock, then you would NOT be needing any neutral connection.
Also, it should have been installed on the lower element for a more accurate reading, since the lower element does 90% of the water heating.
Did you monitor the upper element's or lower element's usage?
kwired
Electron manager
- Location
- NE Nebraska
Incoming water temp will not change how much energy is needed to heat water to desired temp, but will not change how much energy is saved by using an instant vs tank heater. You still have to heat the water the same amount either way.
Incoming water temp will definitely effect how large of an instant water heater is needed to reach desired temp at a specific flow rate, and will effect the recovery time of a tank style unit.
Incoming water temp will definitely effect how large of an instant water heater is needed to reach desired temp at a specific flow rate, and will effect the recovery time of a tank style unit.
boboelectric
Senior Member
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- Eighty Four,Pa.15330
Any thoughts to Demand Charges that are coming with these new smart meters?
kwired
Electron manager
- Location
- NE Nebraska
They are capable of determining when you have a specific amount of demand. Most any question about that probably needs its own thread.
@KBSparky - the clock between neutral/ground and a hot lead is how I currently believe I should have done it way back when, but from what you say this won't work.
How I actually did it way back when was to use 4 ea. 2W resistors in parallel to drop the 240v to 120v. I tapped off the bottom element.
I first assumed this 4w clock was mostly resistive but that idea resulted in considerably more than 120v going into the clock, so I had to raise the value of the dropping resistor.
@RUWired - from 55F, this gives each person 19 gals of 120F water per day. That's pretty reasonable.
How I actually did it way back when was to use 4 ea. 2W resistors in parallel to drop the 240v to 120v. I tapped off the bottom element.
I first assumed this 4w clock was mostly resistive but that idea resulted in considerably more than 120v going into the clock, so I had to raise the value of the dropping resistor.
@RUWired - from 55F, this gives each person 19 gals of 120F water per day. That's pretty reasonable.
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kwired
Electron manager
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- NE Nebraska
Only way it works is to use relay, or some other control method, or a 240 volt connected clock - which sounds like you attempted by putting resistors in series with a 120 volt clock. Two identical 120 volt clocks in series should work also. Just connecting to one element lead and a grounded conductor and leaving everything else as is will result in clock running continuously because the normal control only opens one lead of the 240 volts. you will always have back feed from the other side of the 240 volts through the element. Element resistance is low enough it may have little effect on accurate operation of the clock.
I can't recall whether I used the dropping resistors because I took the element backfeed into account, way back when.
This back feeding is the same reason you can't hook a 120vac humidifier to the heat input terminals of the HVAC blower motor.
When the AC is selected these two input terminals output considerably more than 120v and so they clobber the humidifier transformer.
Close.
2 GPM = 16.6 lbs/min= 0.28 lbs/sec and at @70F rise gives 19 btu/sec = 20 kw, and bathtubs pull more than 2 GPM of 120F water.
mivey
Senior Member
It will eventually lead to higher rates for those with the higher demands, as it should. A reduced utilization factor means less efficient use of facilities.
The instant water heaters take the demand out of the tank and pushes it onto the electric system. This requires a bigger, stronger, less efficient electric supply system and that means higher supply costs.
This brings up another point.
You could get 120F water from a tank heater for a while, long enough to fill a tub.
You could get 6 GPM of 120F water from a 60 kw tankless heater forever, but what house needs this much hot water?
They use these in Germany, but living space there is limited; not so in the US.
You could get 120F water from a tank heater for a while, long enough to fill a tub.
You could get 6 GPM of 120F water from a 60 kw tankless heater forever, but what house needs this much hot water?
They use these in Germany, but living space there is limited; not so in the US.
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