energy use, circulators vs. zone valves


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Old 04-07-06, 01:00 PM
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energy use, circulators vs. zone valves

Was talking with a hydronics person the other day. He opined that “parasitic energy consumption” due to running two heating zone circulators on a system that really only needs one to do the job adequately is a thing to be avoided. Didn't get a chance to ask what zone valves (Honeywell, Taco) draw in terms of power vs. a circulator.

Anyone ever run numbers comparing the two? Say a Taco 007 pump vs. a Taco 570 zone valve vs. a Honeywell V8043E-1061 zone valve?
 
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Old 04-07-06, 02:52 PM
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Energy use

A Taco 007 draws o.71 amps @ 120 volts. A 570 zone valve draws about 0.8 amps @ 24 volts & a V8043 (as memory serves me) draws about 0.4 amps @ 24 volts. The next question is how much does the properly sized transformer for the zone valves draw? My guess is in the long run, the circulator will be cheaper to operate (using an SR 50x switching relay) than the constant draw of the transformer for the zone valve.
Even if it is the most expensive, I'll take circulators any day just for the redunency factor (when one goes down, you still have heat, but if you only have one & it goes down, you're S.O.L.)

Interesting question.
 
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Old 04-07-06, 03:12 PM
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While I agree with Grady that the redundancy in a circulator is the way to go, I have to disagree on the electrical figures.

As I understand it, when the zone valve is not changing state (since the valve only draws current when it's changing from on to off and vice-versa), the transformer is not under load so there is almost no current being drawn by it (a little bit is drawn and given off as heat, but not all that much).

So with Grady's figures, the circulator draws around 85 VA whenever it's on, whereas the Taco valve draws only 19 VA, and that only while changing state. The rest of the time there is minimal draw.
 
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Old 04-07-06, 04:03 PM
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It really is not quite that simple. If you have a number of small-loop zones, the total of which is such that the smallest circulator will handle it, then I prefer to use zone valves. If the loops are small but the total number of loops would require a larger circulator then multiple (smaller) circulators are the way to go.

There is no reason why you can't use a combination of circulators and zone valves if the need is present.
 
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Old 04-08-06, 04:40 AM
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Yes, the draw of the transformer is where I get hung up. The extent to which it's drawing current, the efficiency of the 120V->24V conversion (I think it's about 80%). But I'll guess in the end the zone valves are cheaper to run. Assuming they don't fail way more often than the pump, in which case there goes the savings.

I think Grady's point about redundancy is one of those contributing factors that argue for doing the circulator option. However, an 007 is about the same price as a zone valve head, just takes up more shelf space. Maybe having a spare pump lying around would be the solution. Me, I fire up the wood stove....
 
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Old 04-08-06, 12:22 PM
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In a perfect world it would be the same. One large variable speed circlulator that can ramp up and down to match the number of zones calling for heat versus much smaller circs sized perfectly for the zone they serve.

BTW, I don't think transformers care whether or not they are actually supplying low voltage to their devices. I think their wattage draw is pretty constant. Check your transformers around the house with a watt meter. None of mine care whether or not anything is plugged into them.

Ultimately I think the most efficient way to zone would be TRVs and a load sensing circ or two. Hopefully Wiley will have one on the NA market soon and when that happens, Grundfos & Taco will follow suit. They already exist and are in use in Europe. TRVs require no electricity. In addition, it is possible for circs to use far less electricity than they do now for the same performance. Check out Laing as an example of a low wattage circ.
 
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Old 04-08-06, 03:42 PM
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I don't have a wattmeter, but I can't really see that as being true. Conservation of energy says that the electrical energy drawn by the transformer has to go somewhere. When a transformer has a load, the energy from the line is carried to the device and used there. If there is no load on the transformer and it's still drawing the same amount from the line, where would the energy go? The only place is heat.

If the energy drawn by the transformer was constant, it would have to get much hotter when _not_ loaded, and cool down when under load. I believe that if you touch a typical transformer (an insulated one, please!) you'll find it's the opposite - it heats up under load (as higher current causes more heat loss), and cools off when the device is turned off.

Please note - I'm not an electrical engineer, and I am basing this on half-remembered physics and electronics classes in college - so it's possible that I am totally wrong on this.
 
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Old 04-09-06, 11:20 AM
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jgalak is correct

The load on a transformer secondary is reflected back to the primary. The only current drawn by an unloaded transformer is due to parasitics--i.e. the energy lost to self-heating and the charastic "hum." Can't explain why an ammeter reads the same when the transformer is loaded and unloaded, unless the load is so small that it falls outside the resolution of the meter...
 
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Old 04-09-06, 04:47 PM
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A transformer is a pair of inductors with flux linking across the common core. If there is no load on the secondary then none is reflected back to the primary so the only loses are wire losses and eddy currents. However this does not mean that current is not moving, when dealing with AC current is always conducting as long as the circuit is complete however an inductor puts back into the circuit as much current as it takes minus its loses so although current is always flowing it is not using it. If you see no difference when you measure the current with no load on the secondary then your secondary load must be very minimal.
 
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Old 04-09-06, 07:41 PM
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I agree with the theory, however, have you:

Ever had a transformer that is supposedly doing nothing, that has been plugged for a long time doing nothing that didn't actually feel warm to the touch?
 
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Old 04-10-06, 06:25 PM
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A transformer being warm to the touch even while no load on secondary is a direct relation to the power being consumed because the wire in the primary windings have a resistance and since there is either 110VAC or 240VAC applied heat is generated by the power being disapated.

E(Volts) X I (current in amps) = P (power disapated in watts)

With no load on the secondary, is you measure the current flow with a clamp on ammeter and multiply it by the volts across the primary you wil get the power disapated.

Once a load is introduced to the secondary the current flow through the primary will also increase.
 
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Old 04-10-06, 09:52 PM
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Okay so we are both saying transformers waste some energy.
 
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Old 04-13-06, 10:49 AM
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Originally Posted by creepr91
A transformer being warm to the touch even while no load on secondary is a direct relation to the power being consumed because the wire in the primary windings have a resistance and since there is either 110VAC or 240VAC applied heat is generated by the power being dissipated.

E(Volts) X I (current in amps) = P (power dissipated in watts)

With no load on the secondary, is you measure the current flow with a clamp on ammeter and multiply it by the volts across the primary you wil get the power dissipated.

Once a load is introduced to the secondary the current flow through the primary will also increase.
Power in AC circuits is not the same as DC when ever you have an inductive or capacitive circuit you change the phase angle and therefore change the real power. The formula above will not give you the real power consumed by your transformer because it does not take into account the phase relationship. If your transformer was a perfect inductor, which it isn't, your power would be zero because real ac power is (Erms * Irms * cosΘ) which in a perfect case would be (Erms * Irms * 0) which of course equals zero. So you need to work out your actual phase angle in order to get a true measure of your power the formula to work out your phase angle is Θ = tan-1(XL/R) thats inverse tan * (inductive reactance/resistance) which in this case would most likely be very close to 90 there for your real power would be very low. The heat you are feeling are from eddy current loses in your transformer and wire resistance no transformer is perfect but your loses are not large unless you have a very poorly constructed transformer or you are working well beyond its intended specs.
 
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Old 04-14-06, 05:55 AM
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Originally Posted by xiphias
Yes, the draw of the transformer is where I get hung up. The extent to which it's drawing current, the efficiency of the 120V->24V conversion (I think it's about 80%). But I'll guess in the end the zone valves are cheaper to run. Assuming they don't fail way more often than the pump, in which case there goes the savings.

I think Grady's point about redundancy is one of those contributing factors that argue for doing the circulator option. However, an 007 is about the same price as a zone valve head, just takes up more shelf space. Maybe having a spare pump lying around would be the solution. Me, I fire up the wood stove....
I missed this earlier so I will adderess it now, almost all transformers working within spec have an efficiency of 95% or greater. To add to that transformer losses are at their minimum when there is no reflected load.
 
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Old 04-18-06, 07:26 AM
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Interesting info. Sorry to have started the thread then had to go out of town for work.

Sounds like zone valves and transformers use less, particularly if the transformer efficiency is high. After that, it becomes a performance and comfort vs. cost issue.
 
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Old 04-18-06, 06:30 PM
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Wink Start a thread & run

Yeah, I'd bet you'd throw stones at a hornets nest & jump in the pool too, LOL.
 
 

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