Had a bad lower element in my water heater and noticed that the diagram indicated "non-simultaneous" operation. I'm just a little curious about this scheme. Seems odd to me because the hot water is going to rise to the top of the tank either way, right?
Yes, but you want the water at the top to have the first priority when it comes to being turned on, because that's the water that's going to go out of the tank first. Once that's up to temp, then in non- simultaneous operation, the uppers shuts off and the lower turns on.
Hi Dave:
Yes hot water rises. But the way I understand, see a recent post about this same subject; the top heater under the control of the upper thermostat heats the upper part of the tank first.
When temp. there reaches the preset the upper thermostat operates and flips the connection over to the bottom heater under control of its thermostat.
Heating of the lower water then continues until the whole tank is full of hot water. The lower thermostat then opens and heating stops. This is sometimes referred to as 'Flip-flop' operation. Or, in other words the top thermostat is a 'changeover' type while the bottom is 'on/ off', type. Note 1.
The design principle being that the two heaters are not on simultaneously. Also that even if there is fairly heavy usage of hot water at least the top half of the tank is recovering its temperature before trying to heat the whole tank again!
Notes: From the various (North American 230 volt style) tanks seen and numerous repairs, mainly to 40 US gallon style tanks performed here;
1) It would be possible to use an upper style (changeover type) thermostat as an on/off type in the lower position 'in an emergency. 2) It is possible (by moving one wire) for both heaters to come on each under control of its own thermostat; BUT that doubles the amount of electric current flowing during the heating period, so the wiring and circuit breaker or fuses must safely sized. The 'total' amount of electrcity used, to heat up the same mass of water, will be the same. The advantage being that the tank will 'recover' to preset temperature more quickly.BTW with your bottom element burnt out; you will only have roughly half the amount (the upper half ) of hot water ready for use. Are you sure it was the lower element? Although it is more usually one of the heaters, not the thermostats, But a dud thermostat can also result in no current reaching the heating element; especially if something under that cover has got wet!
Any help? Cheers.
Thanks for the replies. The "quick recovery" idea makes sense.
So that is why the bottom element works harder than the top one. In a low use situation the water at the top of the tank may never cool down and only the bottom element need run.
stan wrote in news:9501cbb7-9d3a-438e-9682- snipped-for-privacy@q9g2000yqc.googlegroups.com:
Nope. Bottom goes on first.
Turn on hot water. Hot water exits from the top. Cold water enters bottom. Bottom cools faster. Bottom element comes on. If demand is high and top of tank cools beyond upper thermo min level, upper element kicks on. When upper element is on, lower gets shut off. When top is satisfied, lower kicks back on until lower thermo is satisfied. Lower and upper then are both off.
This is the best description I have found. Red Green may be talking about a different design but everything I've found about this design jives with the link below.
That link is right back to this thread. What Red Green said sounds right and basically all the people I see here are saying the same thing. One problem is a statement that the OP made about the top element heating "first". It depends on what you mean by first. In my reply from years ago I said the upper element gets PRIORITY. If both the top and bottom need heating, the top gets heated first, the bottom is shut off. But Red is right, under normal operation, hot water is drawn out the top and if it's not a lot of water, the cold water entering the bottom will have the bottom element turn on. It can heat the water enough without the upper coming on because the upper thermostat never drops low enough.
Consider another example of "first". Suppose the heater has been turned off for a week. When it's turned on, the upper element will be heating first because both thermostats are calling for heat. That's why saying that the upper element has priority, rather than saying it heats first, is a better way of describing it.
Señor - I have a Lochinvar 50 gallon 9000 watt 240v 2-phase water heater that fires upper or lower or both elements simultaneously.
50 amps? We don't see them in the US, at least not in residential.
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