is 220 cheaper than 115

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don_resqcapt19 said:
How would you use less energy, even in a vacuum insulated bottle? It still takes 1 BTU of energy to heat 1 pound of water 1 degree. I can see the energy use being equal in an ideal closed insulated system, but I don't see any way that operating the heaters at 120 volts will save any energy over operating them at 240 volts.
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Either you misunderstood, or I wrote it wrong :rolleyes:

Same energy in "bottle".

In real world, less energy is used at 240V than 120V to achieve the same water temperature, where R of heating elements is equal.
 
Besoeker said:
If you throw in a whole load of "what ifs" you cant conclude anything.
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Granted. But recall that the salesperson made a statement to the effect that they tested their equipment, and discovered that the 120 volt unit was cheaper to operate. What I am saying is that this is not necessarily a contradiction of the OP's understanding of physics. The salesperson did not make a generic statement that lower voltage systems are cheaper to operate, merely that that was the results of their tests on their own equipment. So I infer that their units are not "otherwise equal."
 
charlie b said:
Granted. But recall that the salesperson made a statement to the effect that they tested their equipment, and discovered that the 120 volt unit was cheaper to operate. What I am saying is that this is not necessarily a contradiction of the OP's understanding of physics. The salesperson did not make a generic statement that lower voltage systems are cheaper to operate, merely that that was the results of their tests on their own equipment. So I infer that their units are not "otherwise equal."
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Well, we weren't present at the exchange between the salesman, the prospective customer, and bnb so we can neither reasonably conclude what the salesman did or didn't claim nor in what context.
bnb chanced upon a conversation about between a spa dealer and a prospective customer. The original post seems to be about the voltage rather than the application.
So, an equally valid inference is that bnb was was making a point about the relative costs of running a piece of equipment at 220V as opposed to 120V.
 
don_resqcapt19 said:
How would you use less energy, even in a vacuum insulated bottle? It still takes 1 BTU of energy to heat 1 pound of water 1 degree. I can see the energy use being equal in an ideal closed insulated system, but I don't see any way that operating the heaters at 120 volts will save any energy over operating them at 240 volts.
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Would a 1000 Watt heater cost more or less than a 4000 watt heater to operate for the same period of time?
 
ultramegabob said:
how does voltage play into motors life? would the same motor wired higher voltage run any cooler?
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Higher voltage means lower current, and lower operating temperature. Take this notion too far, however, and the insulation system might fail, after which the motor will be very hot very briefly, and very cool forever thereafter. :wink: :D
 
infinity said:
Would a 1000 Watt heater cost more or less than a 4000 watt heater to operate for the same period of time?
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Of course the 1000 watt heater would cost much less to operate for the same period of time, but it would not heat the same amount of water or raise it to the same temperature as the 4000 watt one would.
 
don_resqcapt19 said:
Of course the 1000 watt heater would cost much less to operate for the same period of time, but it would not heat the same amount of water or raise it to the same temperature as the 4000 watt one would.
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BINGO!

Watts = POWER.

ENERGY is not just power, it is power over TIME.

(Making up numbers here to illustrate point)
500 gallon spa (in that vacuum bottle) with 2 heater elements; 1000W 120V and 4000W 240V.

With 120V 1000W, it takes 4 hours to heat up the spa. Net ENERGY consumed is 4kWH
With a 4000W heater, it takes 1 hour to heat up the spa. Net ENERGY consumed is 4kWH!

4kWH = 4kWH, no matter how you get there. Current is irrelevant, demand is irrelevant, voltage is irrelevant, 1 phase or 3 phase is irrelevant.

That's how it works guys.

My earlier point was only that because (in this example for instance) the pump MUST run with the heater element, and the smaller heater element is going to take longer to heat up a given amount of water, then the pump will need to run longer and MAY mean more energy will be used FOR THE PUMP.

But Charlie B made a good point: the salesman made what ends up being an unqualified statement. We have no idea if he was comparing equally sized heating elements at 120V and 240V. We have no idea if the 120V unit compensates for a possible longer running time by providing a smaller pump, but therefore less "action" in the spa. We have no idea even if the compared spas held the same amount of water. So really, we cannot answer the question AS POSED. If however we ASSUME that all other things were equal, i.e. same amount of water, same size jet pump, but lower wattage heater on 120V because of circuit size restrictions, then I still contend that the 120V version would likely use more net energy.
 
I would bet the 120v tub would be cheaper to run.

The tubs have jumper pins. Changing the jumpers changes the features available as well as the volts and amps it uses. Like said a 120 most likely would have a smaller heating eliment. A feature that would be lost by changing the jumpers to a lower voltage & amprage is having the heater run while the jets are working. Another option is limiting the number of pumps working at the same time. Such as on a derated unit the water would cool off with jet use and you could only have one section of jets working at a time.
 
Natfuelbilll said:
Maybe, maybe not. If kW demand was irrelevant then the utility could toss all their demand meters.

Yeah, yeah, residential services don't use demand meters, but who said this tub was going in a residence...
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But demand is not metered in amps. It is metered in kVA. Amps times volts; exactly the same thing as watts in a resistive heater load. So the demand on a 1kW heater at 120V is exactly the same as the demand on a 1kW heater at 240V.
 
Natfuelbilll said:
Maybe, maybe not. If kW demand was irrelevant then the utility could toss all their demand meters.

Yeah, yeah, residential services don't use demand meters, but who said this tub was going in a residence...
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It was a "Home Show" the OP said! Must be going to a residence, IMO.
Jraef got the answer in his last post!
The cost for paying the kWHrs of energy matters most when operating a spa. You will have to pay how much your meter registers, no matter where the energy was spent; whether spent on heater coils or on the heating up of supply wires! At 220V, for the same power delivered, the load current will be lower compared to a 115V service. Lower current means IsquaredR will also be lesser.
 
Jraef said:
To illustrate it, I'll use my spa. I ran a 50A 240V circuit to it. When the heater is on and the pump is running full out (it has a 2 speed motor), I have measured the amp draw at about 40A. If that were a 120V circuit, it would be 80A so it would need to be a 100A circuit.
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That, of course, presumes that both the heater and motor(s) are dual-voltage units, and each's can be connected for full power at both voltages.

We know the motor would have to be dual-voltage rated, but some spa heaters use a single element wich runs, say, at 6KW at 240v, but only 1.5KW at 120v.

Usually, these convertible units can not heat while the pump motor is running on high speed, because the combined current exceeds a 20a circuit's capacity.
 
Everything considered, the lower voltage must cost more to heat the water. I think we agree it would take longer to reach the same temperature, and at this same time the water is being cooled by the ambient. We ain't in no vacuum!
 
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